The proper application of building insulation for historic masonry structures is a hot topic in the world of heritage conservation. Owners of historic residential, commercial and institutional masonry buildings have the unique challenge of how to maintain these structures with the latest building technologies without compromising any historic character.
As a topic we routinely discuss solutions for with our clients, we are excited to share Daniel S. Castele, Architectural Conservator & Designer, Peter Meijer Architect, PC, will be presenting at HINDSIGHT 2020 on: Insulating the interior face of historic masonry building envelopes in cold climates: a review of prescribed techniques and pitfalls.
The Association for Preservation Technology & the National Trust for Canada have partnered to present, HINDSIGHT 2020 (October 1-7, 2020), a fully virtual conference, that will explore the role of heritage conservation in the 21st century. Leaders within the architectural, engineering, construction, preservation, conservation, policy, and design communities, will present on the intersection of heritage conservation and technical, design, policy and community issues.
DAN’S PRESENTATION AT A GLANCE
The need to insulate walls of historic buildings to meet ambitious energy performance targets has been a rising concern in the preservation community. Due to preservation code and accepted best practices, it is not viable to add insulation to the exterior of an existing historic building. In response to this a common approach is to insulate the interior face. While this method of wall insulation can significantly reduce heat loss and improve thermal comfort in cold climates, it also raises concerns about damage to historic fabric. This study examines the current guidance available to project teams. Publications from North America and Europe have been systematically reviewed for guidance on retrofit techniques and evaluation methods. The study reveals a wide range of both prescriptive and performance-based recommendations.
This presentation will explain the progressive research behind a comprehensive and in-depth study of guidelines and professional practices related to internal wall insulation retrofits in historic buildings of North America. The study is part of larger ongoing research into net zero historic buildings. For which, the presenters single-handedly collect and review guidelines for trends, similarities, and differences. The presentation will be based both on research gathered from other professionals and first-hand experience and research conducted by the presenters themselves.
KEY LEARNING OBJECTIVES
Explain the issues, risks, and benefits associated with insulating the interior envelope of mass masonry walls of historic structures; Discuss insulation approaches for masonry envelopes offered in existing guidance from the preservation community and government whitepapers; Discuss commonly used wall insulation details in practice in Canada, USA, & Europe; Compare performance-based approaches and prescriptive recommendations.
To learn more about the conference and to register, please visit: HINDSIGHT 2020.
PMA 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. 
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. 
With 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 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. 
Given 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. 
Spray 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.
