In August, 2012, EYP/Architecture & Engineering, Inc. completed a study to identify insulation strategies appropriate to historic buildings that adhere to the Secretary of the Interior’s Standards for Rehabilitation, minimize the impact on the historic character of the subject buildings, and address the issue of condensation. This study was funded by the National Center for Preservation Technology and Training, New York State Energy Research and Development Authority (NYSERDA) and guided by a committee including architects, engineers, scientists, and code officials from NYSERDA, NYS Department of State, and NYS Department of Health.
Prior to the technical report, the Preservation League of New York State delivered 11 training programs on historic preservation and the Energy Conservation Construction Code of NYS – 2010. Our workshop program included both lecture presentations and field sessions that provide hands-on demonstrations and the opportunity for program participants to see implemented energy retrofits of varying degrees of success in historic buildings. Leading up to the training delivery, the Preservation League of New York State (the League) convened a steering committee comprised of architects, engineers, material scientists, NYS agency technical staff, and property stewards. Through a series of over fifteen interviews and with the help of the steering committee, the League developed the core curriculum for the Energy Conservation in Historic Buildings training sessions.
Over 333 participants in workshops held in every region of New York State learned about holistic approaches to energy conservation, the energy code and historic preservation, HVAC and energy conservation, window efficiency, insulation, sealants, and participated in field sessions.
Throughout the Preservation League’s Energy Conservation in Historic Buildings workshop series, questions on appropriate insulation for historic buildings regularly outnumbered those on any other topic. Architects, preservation professionals, and historic property owners had particular concerns about the impact of insulation on condensation and the reversibility of certain types of insulation. Condensation becomes a greater consideration with an increase in R-value, which is a measure of the material’s thermal resistance.
EYP used two buildings as subject properties for this report, the Cambridge Co-op in Cambridge (Washington County) and the Zadock Pratt Museum in Prattsville (Greene County). The Preservation League chose these buildings, both built in the 19th century, as representative of two historic building types common to New York State. The Cambridge Co-op is a three-story brick mixed-use Main Street building and the Zadock Pratt Museum is a two-story wood-frame residence.
The Energy Conservation Construction Code of New York State – 2010 sets a minimum R-value for insulation, as well as other building components. The insulation study looked at four levels of compliance with the energy code standard for insulation – 50%, 75%, 100%, and 125%. The EYP project team used WUFI Pro software to analyze the heat and moisture transport through the building assemblies. They ran this software through a typical one-year cycle for each building and each of the four insulation levels.
For the Zadock Pratt Museum, the project team found that an insulated wall with a vapor retardant paint on the interior did not lead to moisture accumulation within the wall and lengthened the drying cycle of the wall. Without the vapor retarder, however, the wall had excess moisture accumulation on the interior face of the clapboards.
At the Cambridge Co-op, the WUFI analysis demonstrated excess moisture within the masonry, yet the lack of insulation warmed the masonry and reduced the potential for damage due to freeze/thaw cycles. Adding insulation did not reduce the moisture accumulation, but did make the masonry colder. Again, the insulation without a vapor retarder led to moisture accumulation within the plaster wall, as well as on the face of the plaster. This accumulation was reduced with the addition of a vapor retarder.
Because this report focused solely on insulation levels and condensation potential, the project team did not consider important energy saving measures, such as air infiltration reduction.
Despite the importance of stopping air infiltration, more information on how to seal, with what materials, and where, would help historic building owners who often rush to replace windows, insulate walls, and install solar panels in order to achieve energy conservation and efficiency.
Considerations for air infiltration reduction
- Evaluate the air infiltration rate with a blower door test.
- Caulk around windows, doors, and other openings.
- Weather-strip windows and doors.
- Seal foundation-to-wall and wall-to-roof joints.
- Conduct a final blower door test to check post-sealing results.
Considerations for insulation
- Less insulation is needed if the building is heated significantly less than 68-70 degrees in the winter.
- The code typically does not require the addition of insulation if the building owner does not plan on removing either the interior or exterior wall surfaces.
- Consider the wall cavity thickness, if removing the wall surface and insulating.
- Increasing the wall cavity thickness will lead to additional changes that are not recommended by the Secretary of the Interior’s Standards for Rehabilitation.
- Keep the indoor relative humidity low in the winter for insulated buildings.