Tag Archives: historic

Long Term Impacts of Masonry Waterproofing Sealers

Product X works as a masonry sealer, but what are the long-term ramifications of using Product X on masonry buildings? Masonry sealers come in a wide variety of formulations, but how do the various chemical compositions react to environmental conditions and what affect does the formulation have on the masonry? Most masonry waterproofing sealers specified by architects and conservators, installed by contractors, and requested by property owners are based on Silicone (═Si═ ) chemistry. There are three popular groups of silicone based materials being used as waterproofing materials: 1) silicates, 2) the group of silane, siloxane, siliconate; and 3) silicones. Silicates, similar to Product X, provide waterproofing properties by filling the pore structure of building materials with silicon dioxide (SiO2) precipitation. Common silicates are sand, Portland cement, and other natural occurring minerals. Silanes, siloxanes and siliconates provide waterproofing properties by bonding with the substrate. They are often referred to as penetrating sealers. Silicones do not form chemical bonds with the substrate. Silicones provide waterproofing properties by forming a non-bonded film. Such products are labeled as thin-film sealers.
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Silicates
Silicates are most commonly used in crystalline type water proofing agents for concrete. Their use is generally focused on concrete substrates. However, it is known that strongly alkaline, aqueous solutions of methyl silicates can be used to impregnate masonry. Such solutions often depend upon caustic soda for their alkalinity. Impregnation of masonry with such solutions is often disadvantageous, however, particularly due to the high alkalinity. For example, the high caustic soda content of the solution will cause a gradual removal of the organosilicon compounds from the interstices of the masonry by chemical combination with the surfaces of the masonry surrounding the interstitial voids. Moreover, the caustic soda solution reacts with carbon dioxide or other acidic components of the air which gives rise to salting out and the formation of efflorescence on the masonry. (1)

Silane, Siloxane, Silconates
Silane, siloxane, silconates are penetrating type of sealants. Their effectiveness is dependend on the porosity of the substrate and the dosage of repellant applied. Each manufacturer will have unique requirements for the application and dwell time of their sealer. Silanes and siloxanes form a chemical bond with siliceous containing materials. Silanes and siloxanes go through three reactions when applied to a masonry surface: hydroloysis, condensation, and bonding. During the condensation phase, the moisture vapor transmission rate is critical to preventing moisture accumulation behind the sealer layer.

With penetration type sealers, it is critical to the longevity of substrate (masonry) that the moisture vapor transmission of the sealer is actually known. There has been very little third party testing of vapor transmission and each product manufacturer provides varying ways of testing transmission. In addition, the active ingredient content of the sealer formulation and the coverage rate will greatly affect the moisture vapor transmission. In other words, performance in the field will vary greatly from highly controlled laboratory testing.

Siliconates are water soluble and they impart water repellency on porous surfaces. A drawback to using diluted siliconate solution for waterproofing applications is that siliconates react with carbon dioxide and carbonatious matters present in the substrate to form a water repellent, water-insoluble, white colored precipitate. This white layer may become quite visible and require aggressive removal procedures resulting in objectionable appearance or scarification of the surface during removal processes.

Silicone
The effectiveness of silicone sealer depends on the alkyl group used (which directly influences its resistance to alkaline conditions), the amount of exposure to ultraviolet light and the level of moisture in the masonry when the silicone is applied. (2)

The proliferation of masonry coatings on the market, and the continued pervasive use of the coatings, requires the architect, engineer, contractor, and conservator become more knowledgeable on the wide variety of coating formulations, the continued evolution of those formulations, and understand both the right application of the product and potential detrimental effects of using the wrong product on historic substrates.

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CASE STUDY: WASHINGTON STATE UNIVERSITY, DUNCAN DUNN HALL
In preparation of a major renovation, Peter Meijer Architect, PC was retained in 2010 to conduct a general exterior condition assessment of Duncan Dunn Hall on the campus of Washington State University, Pullman, Washington.

Duncan Dunn was constructed in 1926 as a women’s dormitory for Washington State University, then named Washington State College. It is located in the heart of the WSU campus, facing north towards Linden Avenue. First known as the “New Dorm,” the building cost $150,000.00 to build at that time, and could house 140 students. The architect, Stanley Smith, was the head of the department of architectural engineering and was also the official University Architect.
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The predominant material present on Duncan Dunn is a solid brick unit, brownish red in color, and approximately 8” x 3 7/8” x 2 3/8” in size. At the time of assessment the brick had a very prominent unsightly, white coating over 60% of the masonry facades.

WSU-PMAPDX_masonry_sealers-003Believing the white haze was a result of UV degradation of a masonry sealer, PMA conducted Reunion Internationale des Laboratoires D’essais et de Recherches sur les Materiaux et les Constructions (RILEM) tube tests of water absorption on the exterior brick on Duncan Dunn Hall. The area of brick chosen for the test was out of direct sunlight to avoid affecting the results and was conducted during dry weather. No movement of the water over a 45 minute period was recorded during the test. Masonry units, even those constructed with high quality clays under controlled firing conditions will absorb some water. The results of the field test on Duncan Dunn, along with the white surface haze, reinforced the assumption of the presence of a masonry coating.

Communication with WSU personnel and their internal research surmised that “the building may have had a sealer put on after the original construction. [WSU cannot verify the application through original records] but do know [that a sealer] was not used on a regular basis after [construction completion.] Back in the 70’s some “miracle sealer” of some sort was introduced on Campus and used at a few locations. Duncan Dunn Hall was among the buildings [receiving masonry sealers.] Today you can see the remnants of this as a white powdery surface that almost looks like efflorescence. [WSU] does not know the name of [the sealer] product.”

To confirm the presence of the sealer, PMA conducted lab testing via polarized light microscopy (PLM) episcopic microscopy, capillary fusion and Fourier-transform infrared spectroscopy (FTIR) per ASTM D1245 and E1252, respectively. FTIR indicated the material to be Poly(2-hydroxypropyl methacrylate), an initially water-miscible acrylic polymer that in these samples is at present very brittle and sloughs rather easily.Testing confirmed the presence of a “water-miscible acrylic polymer”. Due to chemical breakdown under UV, the chalky coating remaining on Duncan Dunn is no longer soluble in water.Because of the insoluble nature of the white haze, low pressure hot-water cleaning methods would not be successful. PMA recommended the Rotec Vortex cleaning system using a mirco-abrasive mixture of dolomite, water, and air. Ultimately this removal processes was successful with no damage to the masonry surface.

(1) Patent application for new formulation of sealers. (2) Types of Masonry Water Repellents, GSA web site. Information derived from ProSoCo Inc. product literature.

Written by Peter Meijer AIA, NCARB / Principal

Analyzing Historic Masonry Wall Performance

Wilmer-Davis Hall is a residential complex on the Washington State University (WSU) Pullman campus. Built in 1937 by Architect Stanly Smith, with John Maloney, the six-story structure is composed of masonry and concrete with a masonry/brick veneer in the classical and Georgian Revival architectural styles. For a recent feasibility study of the complex, PMA provided an exterior assessment and a limited moisture study utilizing Wärme Und Feuchte Instationär (WUFI), an industry standard application in predicting wall performance to determine how additional insulation may impact the existing constructions and wall performance.

The primary concerns of this analysis included increased potential for freeze thaw action and increased mold growth as a result of added insulation. When historic buildings are insulated the insulation is typically added to the interior of the structure to prevent alterations to the exterior appearance. This often causes the outer layers of the wall to be both colder and wetter as the materials are no longer warmed and dried by the interior heating system. The additional water and more extreme temperatures can result in an increase in freeze thaw action, corrosion of metal reinforcement, and/or increased mold growth.

Additionally adding insulation to a wall changes the location of the dew point within that construction (the point at which vapor in the air condenses into water). A dew point within the middle of the wall can also result in increased moisture within the wall cavity. If a wall has difficulties drying due to any of the above causes it is possible that over the course of several years the quantity of water within the wall will consistently increase. Accumulation of water will exacerbate reinforcement corrosion and mold growth and can result in increased freeze thaw action. This study focused on the following metrics to analyze proposed wall performance: quantity of water in the assembly, quantity of water in each material layer, relative humidity in layers susceptible to mold growth, and isopleths.

MODEL SETUP
As in any simulation analysis a number of assumptions were made regarding the existing wall construction and the proposed design conditions. A variety of different conditions were analyzed in order to explore the range of conditions and variables. Below is a description of the inputs as well as an analysis of the results.

Four (4) proposed wall constructions were analyzed to determine how different types, quantities, and configurations of insulation would impact the existing constructions. The configurations were based on outlined solutions for meeting Washington State Energy Code (WSEC) or providing improved thermal comfort. Two of the proposed constructions meet WSEC (Option 1 and Option 2), while two of the solutions (Option A and Option B) fall short of fully meeting WSEC, but would provide improved insulation values. The options simulated included:

Base Case (Existing Conditions) (R-4.8)
3-1/2” Masonry
1” Air Gap
7-1/2” Hollow Clay Tile Back-Up Wall
1-1/2” Plaster

Option 1 (Meets WSEC) (R-15.4, continuous insulation)
3-1/2” Masonry
1” Air Gap
7-1/2” Hollow Clay Tile Back-Up Wall
1-1/2” Plaster
2” Expanded Polystyrene
Vapor Retarder (1perm)
0” Gypsum

Option 2 (Meets WSEC) (R-20.9, insulation is not continuous)
3-1/2” Masonry
1” Air Gap
7-1/2” Hollow Clay Tile Back-Up Wall
1-1/2” Plaster
3” Batt Insulation
0-1/2” Expanded Polystyrene
Vapor Retarder (1perm)
0-5/8” Gypsum

Option A (R 17.4, insulation is not continuous)
3-1/2” Masonry
1” Air Gap
7-1/2” Hollow Clay Tile Back-Up Wall
1-1/2 Plaster
2” Foamed-In-Place Polyurethane
Vapor Retarder (1perm)
0-5/8” Gypsum

Option B (R-18.4, insulation is not continuous)
3-1/2” Masonry
1” Air Gap
7-1/2” Hollow Clay Tile Back-Up Wall
1-1/2” Plaster
3-1/2” Batt Insulation
Vapor Retarder (1perm)
0-5/8” Gypsum

Materials It should be noted that no material testing was performed during this phase of the project – instead default material properties were chosen from the WUFI database. Materials used include:

  • Masonry: The material ‘Brick (Old)’ was used to simulate the existing masonry. The material is a generic historic brick material compiled from a variety of different bricks and included in the WUFI database.
  • Airspaces: All airspaces were modeled without additional moisture capacity which according to WUFI, models more realistic moisture storage in air cavities.
  • Hollow Clay Tile: The historic drawings indicate that behind the masonry is hollow clay tile. WUFI does not have a default material for hollow clay tile. Instead a masonry material ‘Red Matt Clay Brick’ was used to represent the solid portions of the clay tile. Air spaces were used to simulate the hollow portions of the tile.
  • Historic Plaster: The WUFI database does not have a default historic plaster material. The ‘Regular Lime Stucco’ material was used to simulate the existing plaster.
  • Batt Insulation: ‘Low Density Glass Fiber Batt Insulation’ was used in simulations.
  • Rigid Insulation/Expanded Polystrene: ‘Expanded Polystyrene’ was used in simulations.
  • Fomed-In-Place: ‘Sprayed Polyurethane Closed-Cell’ was used in simulations
  • Gypsum: ‘Interior Gypsum Board’ was used in simulations.


  • Weather/Interior Conditions In each simulation the model was set to mimic extreme situations to verify that the existing walls will perform in all conditions. The Spokane, Washington weather file indicates that the south elevation should have the most wind driven rain and moisture impacting the wall. Given this information the analysis used south exposure and the Spokane weather file to simulate exterior conditions. For the interior climate conditions the following profiles were used:

  • Interior temperatures ranging from 69 °F to 72 °F
  • Relative humidity ranging from 50% – 60%


  • The above values represent a relatively high moisture load which is consistent with the existing use as a residential facility.

    Water Intrusion Additionally as per ASHRAE 160 a small leak (1% of driving rain) was introduced into the exterior assembly to simulation a scenario where water was penetrating the exterior surface. This could occur at bondline failures in the mortar or penetrations through the wall assembly. The leak was placed past the masonry veneer on the face of the hollow clay tile backup wall.

    Initial Conditions Lastly the initial conditions of the materials were determined using ASHRAE 160. For existing wall materials EMC80 was used as the initial moisture content. (EMC80 is a value expressing an equilibrium of water and material masses at 80% humidity). For new components the expectation was that the materials would be installed from the interior and would remain dry during the construction process – thus EMC80 was used for new components as well.

    WUFI RESULTS
    Four metrics were used to interpret and analyze the following WUFI results: Total Water Content/Water Content in Material Layers, Temperature, Relative Humidity, and Isopleths.

    Total-Water-Contents-WSU-Wilmer-Davis-WUFI-Report-6Total Water Content WUFI can predict the total accumulation of water over the time frame of the simulation, in this case five years. Over the course of each year a wall assembly will be wetted by the rain, and dry over the summer months. Differences in humidity and temperature between spaces may cause water condensation within the walls. If conditions do not allow condensation or other water to dry, materials may accumulate water over a period of time.

    The chart above shows how each of the different simulations performed. Note that total water content is measured per ft2 of wall. Walls that are thinner (existing construction) will inherently have less capacity to hold water. In general all of the walls performed in a similar manner – an indication that the retrofit strategies should perform in a comparable manner when compared to the existing walls. As can be seen in the chart, all of the simulations, including the base case showed some accumulation of water over the five year simulation. These results, however, do not conclusively show that the proposed walls will accumulate water. The results indicate that even the base case is accumulating water over time. During PMA’s site visit, however, the existing exterior walls appeared to be performing well – which would not be the case if they were consistently accumulating water. Additional analysis showed that the gradual accumulation of Total Water Content appears to be a result of initial instability within the wall construction that equalizes over time. A 20 year simulation showed accumulation over the first five years, after which the water content stabilizes.

    Water Content in Material Layers Each of the individual layers of material in a wall assembly have the capacity to hold and retain water. A high water content in any individual layer can indicate the potential for mold growth, the possibility for damage associated with freeze thaw, and a reduction in R-Value based on moisture content. Mold growth is possible when the moisture content is above 20% and if the material has the capacity to feed mold growth. The charts below show how each simulation performed for each layer within the wall.

    Water-Content-Materials-WSU-Wilmer-Davis-WUFI-ReportIn general most layers remained well below the 20% threshold for mold growth. The insulation layers, however, are an exception. Options 2 and B both had batt and/or foam insulation which yearly exceeded 20% water. This quantity of water is somewhat concerning for the batt insulation as it may reduce the material’s R-Value and/or contribute to mold growth depending on the composition of the material. Solutions that used foam insulation performed better than those with batt insulation.

    Temperature One common result of insulating a historic building from the interior is increased freeze thaw action. Insulation prevents the interior conditioned space from heating and drying the exterior masonry. As a result the masonry is typically saturated with more water and exposed to colder temperatures. The analysis looked at the temperature within the middle of the masonry to determine how added insulation would impact the material. A chart comparing the base case to the four options for insulation is located below. As can be seen the brick temperature remains consistent with the base case in all retrofit options. This is an indication that the masonry may not by exposed to additional weathering as a result of added interior insulation. It should be noted that not all masonry reacts to water saturation and freezing conditions in the same manner. To further analyze the masonry’s susceptibility to freeze-thaw action lab analysis is recommended to determine material performance. If results indicate that the masonry is susceptible to freeze-thaw it will be critical to ensure new constructions do not lead to a significantly colder/wetter exterior wall.

    Relative Humidity The relative humidity of the air within the wall construction also has an impact on material longevity and mold potential. A high relative humidity in plaster or batt insulation layers may indicate mold growth, while a high relative humidity in layers with reinforcement may indicate the potential for corrosion. A constant and high relative humidity (above 80%) indicates the potential for mold growth. The charts to the right focus on several susceptible layers, the existing plaster, batt insulation, and gypsum board. In general the majority of the layers susceptible to mold remained below 80% relative humidity, or consistently dropped below 80% relative humidity allowing the material to periodically dry. An exception was the existing plaster layer. The addition of interior insulation caused the relative humidity within the layer to increase approximately 15%, from 65% (base case) to just over 80% (all options for added insulation). This spike in relative humidity is concerning and could indicate the potential for mold growth within the layer.
    Materials-Temperature-Relative-Humidity-WSU-Wilmer-Davis-WUFI-Report
    Isopleths WUFI can also predict mold growth by plotting isopleths on the interior surface. The isopleths are plots of the temperature and the relative humidity for every time period calculation. When the temperature and relative humidity both exceed the limiting lines calculated by WUFI there is the potential for mold growth. The simulations indicate that there is very little potential for mold growth. All of the simulations begin above the limiting lines, but over time equalize and remain well below the threshold calculated by WUFI.
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    CONCLUSIONS
    The results described above indicate that there could be some challenges to designing an appropriate insulation system for Wilmer Davis Hall. Three of the primary concerns noted in the above analysis are: increasing total water content quantities; high quantities of water in the batt insulation layers; and consistently high relative humidity’s in the existing plaster layer.

    In general Option 1 and Option A performed better than Option 2 and Option B – primarily because they relied on only foam/rigid insulation. This resulted in no risk of mold growth within the insulation layers and no reduction of the R-Value. Concerns were still identified with both Options in terms of total water content and relative humidity in the plaster layer.

    Prior to detailing a new wall for construction additional analysis is recommended. Minor changes in material properties can have significant impacts on wall performance. The above analysis has indicated that there is a potential for mold growth, but has not confirmed its likelihood. Most of the metrics indicated no risk of mold growth – however because some of the metrics showed a potential for mold, additional analysis is recommended. Testing of the existing materials and specific data on proposed products should be used to refine this analysis and determine extent of mold growth risk.



    Written by Halla Hoffer, Associate, Architect I

    Overview of Architectural Styles in Oregon: 1840s to 1970s

    The City of Gresham applied for and was granted a CLG grant from the State Historic Preservation Office to increase community interest in historic preservation. The City felt that a presentation focused on architectural styles would be likely to generate some interest. They contacted PMA to find out if we would work within their budget and provide a powerpoint presentation geared towards citizens with no planning or architecture background, but also useful for City staff and historians. PMA was happy to be able to provide an overview of Oregon architecture styles from “settlement era” up until mid-1970s. The presentation highlighted the styles most likely to be seen in the Gresham area, especially residential and commercial uses. It was educational for our office to find those historic properties in Gresham and incorporate some of them into the presentation.

    Use, Type, Style
    It is difficult to understand style without an appreciation of the ways style can be overlaid on various types and uses of buildings. The USE of a building is its primary function. For instance, a church (use) might have a hall with steeple (types or forms) and be Neoclassical (style). The use or purpose of a building is strongly linked to its form, but even within a category of use such as residential, one might find various types such as “apartment block,” “bungalow,” or “four-square.” TYPE just means the basic form, so it is useful for historians to categorize these forms into expected sizes or arrangements of volumes. An apartment block is generally a simple rectangular building with several apartment units and a shared entry. A bungalow is simply a small house, one or 1.5 stories, horizontal in expression. Bungalows are often Craftsman in style, but a handful of other styles are sometimes used with a bungalow type. A four-square is a larger house, typically 2 or 2.5 stories, consisting of a somewhat square footprint with 4 rooms on each floor, and a broad front porch with columns or posts.

    The building’s STYLE is determined by the architectural and ornamental details and exterior features applied to the basic structure. Styles change with the times. In fashion and out of fashion, some endure longer. The timeline included is generally reflective of Oregon architectural fashions. However, style also can be affected by technology- for example, the development of steel frame buildings allowed for a new style to emerge: Modernism. Older bearing-wall masonry construction only allowed for small windows set between structural wall areas. A proliferation of new building types, such as the geodesic dome, occurred in the Modern era.

    We categorize buildings by type, use, and style when doing a survey of resources in a particular area. The data can be compared quickly and easily to data from other surveys, so we can see the patterns and history of development emerging in any particular area.

    Stylistic Timeline of Architectural Styles in Oregon
    From Vernacular Forms and Styles, to Renaissance Revivals, Northwest Regional Style and Post Modern, Oregon has a robust and diverse vocabulary of architecture. The stylistic timeline below is meant as a broad overview, highlighting key attributes per style listed, to help you identify your local and regional architectural resources.

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    OR-Arch-Overview-Stylest-4
    Written by Kristen Minor, Associate, Preservation Planner

    The Form and Function of Lighting Design

    When we experience an interior architectural space, lighting plays a large role in setting the mood and functionality of a space. No matter an existing, modern or historic building, light of a space is a critical aspect of great interior design. Lighting elements can be designed to enhance the space and architectural details, set the mood, and compliment furniture, color schemes, and art work. For spaces without an abundance of natural light, lighting design becomes even more critical design consideration. For a recent project, PMA designed lighting schemes for two historic four-story tall interior atriums.

    The existing atriums utilize natural light from skylights above; however the original design provided no artificial overhead lighting in the space. During the winter months or at dusk and night, the light quality of space relies on the little ambient light from the skylights or artificial light from the surrounding rooms and halls. The light during these times is inadequate for the necessary function of the space. PMA was tasked with providing a lighting solution that would sensitively address the historic nature of the atriums and provide adequate visibility in the space.
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    Defining the Project Challenges
    The concepts for our lighting schemes were based on the intended function of each identical space. The focus of the design and specified need of the client was to provide lighting for evening social gatherings, networking, and overall entertaining. Lighting needed to be adequate enough for speakers presenting to a crowd and for listeners to be able to read any related literature. Therefore, it was crucial to design lighting schemes that could provide ample lighting for evening events without compromising the historic integrity and ambiance of each space. To provide a solution for our clients’ challenge, we considered the following when approaching our design for the lighting schemes:

  • How to provide power to the source of lighting without compromising the historic elements.
  • Designing for large volumes of vertical space: hanging lighting within the atrium versus lighting from the top; how the light travels in the space, how it casts down shadows, the reflections off the floor and other surfaces.
  • One atrium exhibits permanent hanging sculptures and art; the lighting design required minimal approach to integrated and highlight the sculpture without distracting from it.
  • Designing for and highlighting the atriums’ architectural details, like the cornices, in addition how to hide or incorporating other non-historic architectural details like the structural support columns.
  • pmapdx-lighting-design-002
    Methodology for Design Solutions
    The prominent design goal was to increase overall light levels through a refined, modern scheme that would provide juxtaposition to the historic architectural elements and hanging sculpture. As in any historic project, it is important to avoid solutions that are faux historic, competing with, compromising, or confusing the original historic character. The few pragmatic design parameters defined by the client allowed for design freedom to provide several unique, distinct solutions. While creating our designs, PMA experimented with the type of fixtures (down lights, sconce, defused) and placement of these fixtures within the large volume of the atriums. PMA explored these options in a Revit model of the atrium spaces, which enabled evaluation of the design solutions through lifelike renderings that portrayed the quality and levels of light. Illuminance studies of lux levels provided a way to evaluate each design and provide refinement to meet necessary levels defined by the function of the space. Some lighting design options included:

  • Design lighting to highlight and contrast architectural features from surroundings, for example placing fixtures in the cove of architecture cornices located above openings within the atrium.
  • One atrium has a glass block floor element which could be illuminated from below to provide a dramatic light feature.
  • Accenting the verticality of the space with defused ribbon lighting set within the non-historic structural C-channels. This would transform these elements into elegant vertical lines leading the eye to the above skylights.
  • Pendant lights interspersed between sculptures would provide orbs of light to highlight elements of the sculpture. These fixtures would provide defused-light with optional downlights within the same fixture.
  • Suspended down lights at top of atrium with lights accenting sculptures from above and side.
  • Wall sconces to accents light and wash the atrium walls and columns; this would provide an overall glow to the space.
  • pmapdx-lighting-design-001
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    Scheme 1 unified serval lighting design ideas to provide different light level options in the space. Wall sconce lights provide general illumination of the space. Large circular hanging fixtures consist of defused tube lights and large circular defused downlights. Each group of fixture types can be controlled independently and dimmed to provide the ambience desired.

    Scheme 2 specifically works with the sculptures in the second atrium space. Vertical ribbon lights provide ambience illuminance of the space while concealing non-historic structural elements. Pendant lights hang interspersed within the sculptural elements. These have a defused light with an option for downlights. Each grouping of fixtures can be illuminated together or separately depending on the quality of light needed.

    Scheme 3 was chosen by the client and until announced must remain confidential. Stay tuned for the reveal.


    Written by Hali Knight.

    Using Revit for Historic Architecture

    Revit is used widely for designing new architecture and for documentation of existing structures. When first looking at Revit one may assume that it is tailored for use with contemporary designs. The default ‘Families’ (the term Revit uses to describe all types of elements from furniture to windows, doors, annotation symbols, wall constructions, etc.) are all generic to new construction. Despite the pre-set generic components, Revit’s strength lies in the ability to create custom ‘Families’ and its capability of tracking both three dimensional design as well as linked information about components. When used correctly Revit can be a powerful tool for building assessment and historic renovation. At PMA we have found several tools in Revit that can help us accurately show historic elements, track information about conditions, show repair strategies, and graphically present data.
    Revit-RecordingData
    When working on historic structures it can be very important to accurately show existing elements. We often need to indicate exact pieces of terra cotta that require replacement or how a stone entry stair is configured so that the cost for replacement stones can be correctly estimated. We frequently create custom ‘Families’ to accurately show historic detailing. ‘Families’ of all types can be created to refine a model and add historic detail. Some of the common custom elements that we create include windows with historically accurate profiles, stacked walls that let us show terra cotta banding and differentiation in materials/wall thicknesses, complex historic roof structures, and custom patterns that match existing stonework. By adapting the generic Revit ‘Families’ and creating our own we are able to accurately represent historic features and structures.

    Capabilities
    One of Revit’s most useful capabilities is its ability to record and track information about building components. Unlike earlier drafting and 3D modeling applications, Revit can store information about material finishes, specification references, and much more! In Revit you can assign ‘Parameters’ to ‘Families’. ‘Parameters’ are used in a variety of different ways – but one of the most useful we’ve found is their ability to track the condition of specific building elements. For example, when we perform window surveys we can assign ‘Parameters’ to all of the modeled windows that describe the typical deficiencies observed. For each individual unit we can then record what deficiencies were discovered in the field. Once all of the information has been added to the Revit model you can create schedules in Revit to describe the condition of each window unit and total quantities. The information can be extracted from Revit and into spreadsheet software to analyze the data, present trends, and identify repair scopes for individual units.
    Revit-Filters
    Using Fliter’s
    Revit’s ‘Filter’s’ function is another tool that we use in conjunction with ‘Parameters’ to better understand and present information that we’ve recorded in the field. Filters allow one to alter the graphics for components based on their ‘Parameter’ values. For example we commonly use ‘Filters’ to graphically show the condition of a building’s windows after a survey. We do this by creating a condition ‘Parameter’ where a value can be assigned to each window, for example, good, moderate, and poor. We can then use filters to highlight all of the windows in good condition green, those in moderate condition yellow, and those in poor condition red. Unlike a window schedule which may require some analysis – the color coded elevations Revit can create with ‘Filters’ are easy to understand and an excellent tool for presentations.

    At PMA we have found Revit to be an invaluable tool that we use day to day for a variety of uses including 3D modeling, displaying point clouds, rendering, tracking information, and presenting data. Revit is a capable tool and with a little creativity one can tailor the application to complex historic projects. The ability to create complex custom ‘Families’ that track data about the structure make it possible for our office to efficiently record, analyze, and present date we observe in the field – bringing projects all the way through development, documentation of construction documents, and construction itself.

    Review our ongoing building envelope project that utilizes Revit.

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    Written By Halla Hoffer, Associate, Architect I

    When Field Performance of Masonry Does Not Correlate with Lab Results

    First presented at RCI 2015 Symposium on Building Envelope Technology, Nashville, TN

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    Background
    When it was completed, Grant High School was typical of the high schools constructed by Portland Public Schools in the pre-World War II era. In addition to being an extensible school, including educational buildings constructed between 1923 and 1970, the school was also reflective of fire-proof construction through its use of a reinforced concrete structure with brick in-fill. (Portland Public Schools, Historic Building Assessment, Entrix, October 2009)

    Over the last fifteen years, Portland Public Schools (PPS) noted an accelerated degree of masonry face spalling on the original 1923 main building and 1923 Old Gym particularly when adjacent to concentrated sources of surface water. Other areas of spalling were not as obvious including protected wall surfaces. The masonry spalling was not occurring on later additions including the north wing (circa 1925), south wing (circa 1927), and auditorium building (circa 1927). Upon closer visual examination, it was observed that individual units were failing in isolated protected areas of the wall surface. Failures in such areas could not be accounted for under direct correlation of heavy water intrusion and typical failure mechanisms.

    The failure of the brick was potentially due to a number of separate or cumulative conditions including 1) excessive water uptake by the brick; 2) sub-fluorescence expansion of salts in the masonry, 3) freeze thaw; 4) low quality of the original 1923 brick; and 5) the application of surface sealers preventing water migrating to the exterior surface.

    grant-hs-multi-surface-deficiencies

    Field Investigation
    In order to determine if the damage to the masonry was deeper than the surface, several wall-lets, an invasive exterior wall opening, were performed confirming the assembly of a multi-wythe masonry wall constructed in a typical fully bedded bond course with interlocking headers and no cavities between the first three brick courses. Hooked shaped, 3/32” gage, steel wire masonry ties in alternating courses and approximately twelve inches (12”) on center ties were found to be in good condition with no deterioration. The absence of corrosion on the in place brick wire ties indicated that little moisture was present inside the multi-wythe wall.

    As a result of the hypothesis and field observations, it was prudent to conduct a series of lab tests to the brick, mortar, and patch materials to assist in the determination of 1) the quality of the brick; 2) the physical composition of the brick; 3) the quantity of naturally occurring compounds in the masonry and mortar, particularly salts in the masonry; and 4) the quality of the mortar. The findings would help narrow the potential cause of the spalling and lead to a more focused repair and maintenance process. Bricks were removed for testing of Initial Rate of Absorption (IRA – a test for susceptibility to water saturation) freeze thaw testing, and petrographic analysis, a way to determine the inherent properties of the clay and manufacturing process. Both pointing and bedding mortar samples, as well as, the previous patching material were removed and also tested. To rule out damage caused by maintenance procedures, faces of the brick material were sent to determine if sealants were used on the brick and, if present, determine the sealant chemical makeup. The presence of a surface coating may lead to retention of water within the brick and thus prevent natural capillary flow, natural drying, and water evaporation.

    grant-hs-field-testing

    Testing & Results
    Samples sent to the lab for coating assessment were analyzed via episcopic light microscopy, and Fourier- Transform Infrared Spectroscopy (FTIR) per ASTM D1245 and ASTM E1252. The results found no hydrocarbon or organic formulations used on the surface of the brick refuting the hypothesis of a surface sealer.

    Following modified ASTM standards, a 24-hr immersion and 5-hr boil absorption test on the brick were performed. The brick have a very low percent of total absorption at 9.5% for the 5-hr boil and 7.5% for the 24-hr test. The maximum saturation coefficient is 0.79 which is 0.01 over the maximum requirements for Severe Weathering bricks recommended for Portland climate (ASTM C216-07a Table 1). The Initial Rate of Absorption (IRA) is 5.7g/min/30in2 which equates to a very low suction brick or brick with low initial rates of absorption. The freeze thaw durability tests resulted in passing performance. All of these tests refuted the hypothesis that freezing temperatures were the cause of masonry spalling.

    A brick material analysis was performed in general conformance with ASTM C856, ASTM C1324 (masonry mortar) and included petrographic analysis, chemical analyses, x-ray diffraction and thermogravimetric analysis. Samples were analyzed under a polarized light microscope for information such as materials ratio and presence or absence of different deterioration mechanisms. These tests were used to assess the overall quality of material, presence of inherent salts, excessive retempering, cracking, ettringite formation, and potential alkali‐silica reactivity.

    grant-hs-electron-microscopy-salt-deposition

    The Petrographic Characterization resulted in the most unusual findings and the most relevant results related to the observed failures. The polarized light microscope indicated carbonate based salt crystals seeping into the masonry from the mortar. No sulfate based salts, typically associated with the clays used for making brick, were present. Furthermore the inherent properties of the brick showed very small rounded voids and interconnected planer voids. Planner voids result from poor compaction during the raw clay extrusion process prior to firing.

    Performance of brick in the field is a result of both material properties and resistance to micro-climates within the brick’s capillary void structure which cannot be repeated in the lab. Studies have shown a connection between small voids in the material property and susceptibility to longer water retention near the surface. With natural absorption properties, the brick is taking in a small quantity of water in very small pores. 24-hour immersion results are very low (7.5%). Publication of more in-depth studies correlates maximum saturation values for brick with low 24-hour immersion values. The effect of low immersion values and small quantities of absorbed water may increase the susceptibility in brick with small pore structure to freeze thaw failure.

    The presence of salt migration out of the mortar and into the brick, plus small pore structure and low immersion values, combining with a cleavage plane resulting from manufacturing are contributing to the Grant High School brick spalls. Brick with smaller pores are less capable of absorbing the expansive forces of freezing water and drying salts. Interlaced pores creating linear plains parallel with the face of the brick create stress failure points resulting in surface spalling. Since the characteristics of the brick resulted from the firing and manufacturing process, the brick will remain susceptible to the failure mechanisms.

    Conclusion
    Field observations of masonry failures generally correspond with known failure mechanisms. However, it is not unusual that further analysis is necessary to confirm in-field performance and that typical laboratory test results are in conflict with in-situ performance.

    The best corrective action is to minimize the amount of surface water and proper mortar joints and mortar composition. Additional spalls are likely to occur in the future due to the accumulation of expansive forces over a long period of time. Replacement of the spalled bricks is recommended over further patching. Leaving spalled brick in place will continue to worsen the condition over time and affect adjacent brick.

    grant-hs-present-day


    Written by Peter Meijer, AIA, NCARB, Principal

    Assessing Union Station to be Part of Our Future

    Portland’s Union Station is the only major railroad station built in Oregon, and one of the oldest major extant passenger terminals on the West Coast. From its inception, Union Station has functioned as a major transportation link to Portland and the west coast, with a continued vital role to play in future rail and multimodal transportation planning.
    Union-Station-Historic-photo
    A Sense of Place
    Critical to adapting Union Station, and other historic structures, for current and future use is to thoroughly understand key elements and components that convey the sense of place and rich history of the structure. A deeper understanding enables informed decisions to be made about the potential of key characteristics to remain for future generations. Union Station was constructed between 1892 and 1894 and was designed by Van Brunt & Howe architects in the Queen Anne style with Romanesque detail. From 1927 thru 1930, the Main Concourse was modernized by Portland’s internationally known architect, Pietro Belluschi, to reflect the streamline era of rail technology. Like the original 1892 elements, the Belluschi modernization’s are equally important stories to tell.

    Creating a graphic document annotating “changes over time” is an essential tool for evaluating how Union Station has adapted to improvements in rail technology, fluctuations in passenger volume, cultural shifts regarding train travel, as well as modifications to specific architectural elements that impact the historic integrity and interpretation of original design intent.
    Union-Station-Report-Outline-pg2
    Methodology for Assessment
    Our method of developing the graphic drawing is to compare historic floor plans and historic photographs to current plans and images through a process of layering plans from different eras over one another and drawing the altered, or missing, elements (e.g. walls, furniture, spaces, etc.) in different colors. This methodology provides an easily interpreted floor plan. The use of color enhances the image and creates a visual record of both changes and original historic fabric. In reading the graphic drawing, it becomes readily discernible that changes include: wood floors replaced with concrete and new floors added; openings in the main concourse were moved and enlarged; the women’s waiting room and toilet were removed to widen the south hall, the stairs were renovated, and a new baggage counter was constructed. The covered concourse was glassed in and a section was made into the First Class Lounge, which remains today. And in the 1940s, a nursery, or crying, room was added.
    Union-Station-PMAPDX-drawing
    What is fascinating about the history of a building like Union Station, is that the rail lines and street patterns are also integrated with the function and use of the structure and have changed over time as well. The construction of Union Station came soon after Portland was fully connected by rail in 1883 to California, Montana, and rail lines running to the East Coast across the U.S. The Spokane-Portland-Seattle rail connection was finished in 1908. In 1922, Union Station became accessible to all major passenger railroads operating through Portland.

    When originally constructed, six passenger car rail lines approached the rear of Union Station. The waiting platform consisted of planks on dirt with no canopy. The block across from Union Station consisted of a small restaurant, bar, other stores, and stables. A five foot iron fence bordered a large lawn and sidewalk to the south and west of the station. The High Shed, a large two-story metal shed was the first canopy built to cover the passenger platforms and extended perpendicular to the station. Under this High Shed, two smaller scale platform canopies were erected paralleling the tracks. A mail canopy was built at the north end of the building in 1915.

    By 1920, the block across from Union Station’s main entrance had been converted to parking to relieve congestion. As automobile use increased throughout the city, parking configurations were constantly changing over the years. By 1923, an elevated walkway was built to connect the Broadway Bridge to the main entrance.
    union-station-pmapdx-changes-overtime

    With the introduction of larger diesel locomotives and potential for high speed rail along the northwest corridor, the track, platforms, and canopies have had to be modified. Safety and accessibility have also driven the need for changes and modernization. Documenting these alterations with graphics, provides a foundation from which to advocate for further refinement while recognizing historic precedent and protection of historic elements.

    union-station-pmapdx-historic-photo

    Written by Peter Meijer, AIA,NCARB, Principal

    PMA is part of the DOWA-IBI Group team for this exciting PDC Union Station Renovation Project.

    How to Improve Energy Efficiency in Historic Buildings

    As historic architects we find window replacement projects to be particularly challenging — removing original materials from a structure can fundamentally change the design aesthetic. Our built environment must evolve to support more sustainable living, but finding the best way to achieve this goal for historic structures, while minimizing any aesthetic impacts, is an ongoing challenge.

    When looking to improve energy performance the first inclination is often to replace the component with the lowest thermal resistance – the windows. Single pane historic windows provide minimal thermal resistance and contribute to heat loss through the building envelope. But is window replacement really the best option for reducing the carbon footprint of a historic building – how does it compare to other strategies?

    energy-analysis-West ElevationPMA recently performed an energy analysis study to answer that question. The project was to provide quantitative data on the energy savings associated with window replacement versus insulating exterior walls. We choose to study a structure on the brink of historic status – a 1960’s multi-story residential structure with large character defining view windows. The structure is composed of concrete walls, beams, floors, and columns with single pane aluminum windows. The existing building has approximately 36% glazing and no insulation.

    The analysis we performed compared seven retrofit strategies ranging from minimal code compliance to super insulated walls and windows. Details on the specific constructions, r-values, and glazing properties are outlined below.

    Construction Types Chart A wide range of constructions were chosen in order to see the full range of possible results. Future studies may focus on more refined material choices and a narrower set of parameters. The analysis was run in Autodesk Green Building Studio which is an excellent tool to perform basic energy models. While GBS does not allow for complex simulations it can quickly and accurately compare a variety of different design alternatives.

    We chose to look at four different indicators to compare the results:
    • Energy Use Intensity (EUI) indicates how much energy is used per square foot per year and is a very common way of comparing how different buildings perform.
    • The quantity of electricity used per year indicates how much energy is used on cooling loads, heating loads, interior loads, and lights.
    • The quantity of fuel used per year indicates primarily energy used for heating.
    • The annual peak demand indicates the maximum amount of energy used at any single time over the course of a year.

    We assessed the data in terms of percentage improvement over the Existing scenario. The charts below provide a comparison of the seven different retrofits.

    Results Chart

    The Results
    What is intriguing in the results is the large difference in performance within the glazing retrofits options between the Double Pane LoE Glazing and the Triple Pane Glazing. While the Double Pane Glazing provides a notable improvement to the building’s energy performance it is still surpassed by all of the other retrofits. Conversely the Triple Pane Glazing far out performs all of the insulation retrofit strategies. The range between the two glazing retrofits indicates that new windows have the potential to have a substantial impact on energy performance. Unfortunately triple pane glazing is typically cost prohibitive and the LoE coatings applied to achieve maximum efficiency are incongruent with historic buildings. As technologies change and improve it is possible that these obstacles will be overcome – potentially making window replacement for energy efficiency purposes a more viable option.

    window-detailWith current technologies the results indicate that adding insulation to a building has the most cost effective impact on energy performance. Installing new insulation is typically less expensive than window replacement and the results of this study show that Code Compliant (R-~7) insulation can have a significant impact on overall energy usage, outperforming Double Pane window replacement. Interestingly, the results also indicate that a High Insulation (R-25) retrofit performs better than a Combined Retrofit with Code Compliant Insulation (R-~7) and Double Pane Glass.

    The results clearly indicate that adding insulation is an excellent way to improve energy performance without impacting the exterior façade of a historic building. Like any retrofit, insulation poses its own challenges: can it be installed on the interior without affecting historic finishes? Will changes in the temperature of the wall cause deterioration?, etc. Conversely, there are instances where window replacement is the right choice (when the existing windows have reached the end of their lifespan) and in this instance choosing a double pane glazing option can improve energy performance. In most cases, if you are looking to improve the energy performance of your building – it is more effective to explore insulation retrofit options rather than window replacement.

    Written by Halla Hoffer, Architect I

    The Challenge of Insulating Historic Buildings

    A Limited Moisture Study

    At its core, architecture in the Pacific Northwest is closely linked to moisture. The damp climate in Portland, Oregon has an impact on how we design new buildings as well as how we retrofit existing structures. Choices in construction, insulation, and flashing systems are always informed by our understanding of water. The success of any building envelope can be determined by how it performs against condensation, humidity, and water infiltration. Adding insulation to historic buildings is particularly challenging because the added material can change how a building envelope functions, leading to future moisture issues. At PMA we use WUFI to simulate and analyze how proposed retrofit strategies may impact the historic building envelope. For a recent project, we performed a limited moisture story of an unusual exterior brick wall that was to receive interior insulation. We studied how variations in insulative material and construction could impact the durability of both the brick and the interior wall structure.

    The challenge when insulating a historic building is to protect the masonry from excessive moisture and cold. In uninsulated masonry walls, the building’s heating system warms and dries the masonry from the interior. If insulation is added, the masonry typically stays colder and wetter for longer periods of time, which can lead to deterioration. The intent of PMA’s study was to evaluate the masonry for future deterioration and to also identify any potential for condensation/moisture in the insulation cavity. WUFI was used throughout the design process to provide feedback on potential constructions and inform critical material decisions.

    The building was built in 1921 and is unusual given that the original envelope consisted of a two wythe masonry wall with an interior plaster finish. A two wythe masonry wall is not common as it provides limited structure or protection from the elements. The renovation included an extensive seismic retrofit and the installation of new insulation to compensate for the existing wall’s limited structure. PMA was brought onboard to provide feedback on the building envelope detailing. We began our analysis by comparing the performance of the proposed envelope with that of the original building.
    Constructions-Existing-building-envelope-pmapdx

    Constructions-Proposed-building-envelope-pmapdx

    As shown in the illustrations above the existing construction (small drawing) was: 8” of masonry on the exterior, an airgap where wood lath separated the masonry from the plaster, and approximately 1” of plaster on the interior. In comparison the proposed construction (large drawing) consisted of: the existing 8” of masonry on the exterior, a 1/2″ airspace, 1/2″ inch plywood sheathing, 6” of fiberglass batt insulation, a vapor retarder, and 5/8” gypsum with paint on the interior. The first step in our analysis was to accurately model each of these constructions in WUFI. Accurate material modeling is especially challenging in historic buildings. WUFI uses five different material properties to calculate moisture and heat movement. While an extensive built-in database exists for new materials, significantly less information is available for historic materials. PMA often tests materials to determine their properties and adds them to our expanding database of historic materials. The scope of this project didn’t allow for additional material testing. However, we ran several iterations of the analysis with different historic masonry materials to determine a baseline for our analysis. The remaining materials were chosen from WUFI’s building material’s database.

    ProposedBrick-RelativeHumidity-pmapdx-wufi

    ExistingBrick-RelativeHumidity The results of the initial analysis indicated that as might be expected the masonry was not only exposed to longer periods of cool temperatures, it rarely was capable of fully drying. The two charts at the right show the relative humidity in the original construction and the proposed construction where each vertical line marks a calendar year. Note that a relative humidity above 95% indicates a likelihood of condensation. As can be seen in the original construction, during the wet months the relative humidity hovers at about 95%, but drops off significantly during the warmer months. Alternately in the proposed construction the relative humidity rarely drops below 95%, indicating that moisture is present in the masonry almost year round. When the individual layers are examined it becomes clear that in addition to considerable moisture in the masonry itself, water is likely to condense within the wall cavity. As seen in the series of charts below the relative humidity remains high through the airspace and plywood only dropping off between the exterior and interior face of the insulation.

    ProposedLayers-RelativeHumidity-pmapdx-wufiGiven these initial results we suggested a redesign of the insulation system. The existing two wythe wall was not capable of adequately protecting the interior of the building, and the redesign had to accommodate for water infiltration through the masonry. Two options were discussed A) treat the masonry as a veneer wall and install waterproofing to the exterior face of the plywood as a drainage plane or B) install insulation that could be exposed to moisture and water. The constructability of Option A was significantly more complex than that of Option B so our initial analysis focused on Option B.

    Constructions-ClosedCell-pmapdx-wufi

    Constructions-Hybrid-pmapdx-wufiSpray foam was identified as an alternative to the original batt insulation because it can both serve as a vapor retarder and insulate even when exposed to moisture. Two design options were investigated to determine the extent of closed cell foam necessary to adequately protect the interior surfaces from moisture. As can be seen to the right we investigated a construction filled entirely with closed cell polyurethane foam vs. a cavity filled with a combination of closed and open cell polyurethanes. Additionally we looked at the condition of moisture/heat transfer at the perceived weakest point in the structure, where the structural framing was only barely (1/2”) separated from the masonry. The structural integrity of the seismic upgrade depended on a minimal distance between the framing and the existing masonry, but concerns existed as to whether the wood would be exposed to enough moisture to cause mold.

    At the conclusion of the study the spray-foam hybrid option was chosen for further detailing and construction. The combination of closed and open cell foams effectively protected the interior from moisture and condensation. In each renovation scenario studied the exterior masonry was exposed to similar conditions; including increased moisture and cooler temperatures. Given every strategy resulted in similar conditions it was the combined performance of the hybrid system that stood out to the design team.

    When the assembly is studied at the structural members, the interior components (plywood and gypsum) retain their low relative humidity. It is important to note that in this scenario the exterior face of the structural wood members are at above 80% relative humidity year round. These conditions may facilitate the growth of mold according to ASHRAE 160-2009. It is recommended that moisture protection be applied to the outer potion of these members.

    When the assembly is studied at the structural members, the interior components (plywood and gypsum) retain their low relative humidity. It is important to note that in this scenario the exterior face of the structural wood members are at above 80% relative humidity year round. These conditions may facilitate the growth of mold according to ASHRAE 160-2009. It is recommended that moisture protection be applied to the outer potion of these members.

    This chart shows the hybrid option of using both open and closed cell polyurethane foam to insulate and weatherproof the building. The relative humidity remains high at the exterior components, but is reduced to well below 80% on the interior components.

    This chart shows the hybrid option of using both open and closed cell polyurethane foam to insulate and weatherproof the building. The relative humidity remains high at the exterior components, but is reduced to well below 80% on the interior components.

    When only closed cell polyurethane is used to fill the cavity the performance is similar to the hybrid scenario. This chart shows that the outer components are constantly at a high relative humidity while the interior components remain more closely linked with the interior conditions of the building.

    When only closed cell polyurethane is used to fill the cavity the performance is similar to the hybrid scenario. This chart shows that the outer components are constantly at a high relative humidity while the interior components remain more closely linked with the interior conditions of the building.

    Ultimately, the project serves to show how an iterative approach to designing building envelope retrofits is critical to achieving an effective solution. By carefully modeling and simulating the initial proposed system we were able to provide critical feedback that led to a more effective and responsive design. In this case, fully understanding the unique two wythe wall system was essential to providing adequate moisture protection for the wall cavity. While a typical masonry wall is capable of preventing water intrusion, the minimal depth of this masonry wall proved insufficient. Our analysis uncovered this flaw and allowed the system to be redesigned to work more effectively. Unlike new construction where the entire envelope system is designed simultaneously, with historic buildings we must work backwards from the existing to create a cohesive design that responds to and compliments the original elements. WUFI serves as an essential tool in understanding the existing and investigating the new.

    Written by Halla Hoffer, Architect I

    Steps to Replacing Historic Wood Windows

    QAHSC-landmarks-review-pmapdxOur first choice, and ethical preference, is to retain historic wood windows. Repaired and maintained wood windows constructed of old growth lumber will outlast any modern alternative. We advocate strongly for a process and philosophy that seriously evaluates retaining original material. The best approach compares long-term costs, embodied energy, and cultural importance relative to the same criteria for new replacement material.

    But what do you do when the comparative process favors new material and replacement becomes the option of choice? And how do you gain jurisdictional and historic approval for removing character defining features from a historic property? Correct research, documentation, presentation, and material selection are the key factors to successfully replace historic wood windows.

    Lack of maintenance is rarely accepted as a justifiable rationale for window replacement. Arguments for window replacement based on peeling paint, surface tracking of the wood, and/or glazing putty failure are typically countered with comments that benign neglect is a conscious act and straight forward maintenance will reverse the deterioration and deficiencies noted. A better strategy is to base replacement rational on existing significant deficiencies that require financial investment and resource allocation to repair the deficiencies.

    QAHSC-landmarks-review-windows-pmapdxMost existing, older properties have had more than one owner. Research into original design documents, major rehabilitation projects, building permit requests, and other documents provide insight into processes that might have replaced original material. The removal and replacement of non-original material is justifiable and acceptable rationale.

    Documentation by means of an on-site, window by window survey is the only method that will yield quantifiable data regarding the physical condition of existing wood windows. The resulting comparative data is critical for structuring an argument in favor of replacement. The field observations also provide invaluable information pertaining to the means and methods of construction and conversely deconstructing, or removing, the windows. Understanding wood window construction is important to understanding how wood window fail. Source documents like the Association of Preservation Technology’s Window Rehabilitation Guide for Historic Buildings (1997) and the National Park Service Preservation Briefs: 9, The Repair of Historic Wooden Windows provide exploded diagrams of both wood window construction and typical failure locations. These locations generally include the sash mortise and tenon joints, the exterior stops, and horizontal rails. The field assessment will need to document the quantity, location, and extent of any failed components.

    QAHSC-landmarks-review-pmapdxAfter a thorough evaluation and understanding of the existing wood windows, the next decision is to choose a replacement product. In-kind replacement,(i.e. wood window for wood window; true divided lites for true divided lites, matching pane divisions, etc.) is preferred. When the replacement window is virtually identical to the historic window, it is hard to say no. Absent exact replacement, the visual qualities exhibited by the cross section profiles, the sash height and width, and the proportion of wood to glazing, are the most important attributes to match. Appearance from the exterior will trump appearance from the interior during a historic review approval process.

    How the research findings, existing conditions, and replacement products are presented is fundamental to a successful request to replace historic wood windows. Agencies and commissions with jurisdictional review and approval authority require clear, methodical, and linear processes to understand the research, findings, and selection process. Collating the field data using charts and graphs, including graphic representation of previously altered windows, and defining the quantity of failed components will assist a decision in favor or replacement.

    QAHSC-window-flashing-pmapdxWhen an opportunity to retain original fabric/windows is available, the opportunity should be incorporated into the work. Even retaining as little as 20% of historic fabric will increase the likelihood of approval for replacement of the remaining components. The retention of historic fabric also allows successive generations to better understand the history and changes of an existing property.

    Written by Peter Meijer AIA, NCARB, Principal.