At a recent round-table meeting on sustainable historic preservation, I was struck by how much alignment there is between preservation and green renovation. Now, green renovation is a wide and diverse field, and some of the deep energy retrofit people probably don’t have the same opinion on sustainable preservation standards as I do, but disagreements just help to keep things interesting and further the conversation.
I certainly have my issues with historic commissions. In fact, my local group managed to cause enough delays in approval of a new house for myself that I have put the whole project on hold until the economy picks up.
The Secretary of the Interior’s rehab standards
Following the discussion, I located a document that the speakers referred us to The Secretary of the Interior’s Standards for Rehabilitation and Illustrated Guidelines on Sustainability for Rehabilitating Historic Buildings. (Man, is that a mouthful!)
The book (or pdf document if you prefer) is a reasonably well thought out guide to making appropriate decisions on sustainable rehabilitation projects. It was designed to expand on and replace a small chapter on Energy Conservation in earlier guidelines.
The guidelines appropriately recommend doing building diagnostics before undertaking energy efficiency work – always a good idea. They prioritize weatherization appropriately – insulate attics, insulate crawl spaces, and fix air leakage before insulating walls and replacing windows.
Saving old windows
Speaking of windows, this is probably the biggest issue with preservationists – they look to save existing historic windows in almost all cases, with very few exceptions. Recommendations for existing windows include repairing sashes, adding weatherstripping, and adding interior or exterior storms to improve performance – steps which very often provide better value and are overall as sustainable as, or more sustainable than, window replacement.
The guidelines promote operable windows for natural ventilation, open porches, shutters, and awnings for shading and passive cooling, vestibules, the use of natural light, and low VOC finishes. Some other key concepts they promote, all very logical, include not insulating wall cavities that are susceptible to water infiltration and installing renewables only after all efficiency improvements are implemented. I like the way they think!
What about spray foam?
I found only one area where they guidelines and the speakers at the round-table separate themselves from standard green renovation practices – their fear of foam insulation. The major issue is their concern with reversibility, followed by a fear of creating moisture problems by using it.
On the first issue, I believe that they are not properly distinguishing between low-density and high-density foam. Low-density (or open-cell) foam can be removed without damage, and while it may leave some residue that non foam insulations don’t, I don’t believe that it should be dismissed out of hand. High-density or closed-cell foam is often more difficult to remove, and while I don’t fully agree with the concept of reversibility, I will concede this point to the historians.
On the second issue, two speakers at the round-table responded to a question about spray foam insulation by stating their view that it often traps moisture and causes structural damage. In addition, the National Trust website states, “Spray foam insulation … can hinder airflow and lead to the rotting of timber-frame members.”
While this issue is not explicitly stated in the guidelines, it is often repeated, I feel incorrectly, by preservationists. Spray foam is one of the best ways to improve the performance of an existing building, and when installed correctly and in the proper location, won’t create any more moisture problems than any other type of insulation.
Here is to hoping that in the name of better building performance, there may be some flexibility in their future guidelines.
Old thinking is new again
In doing research for this post, I ran across this short piece on windows on the National Park Service website, which I think provides a good guide for sustainable design: “Early builders and architects dealt with the poor thermal properties of windows in two ways. First, the number of windows in a building was kept to only those necessary to provide adequate light and ventilation. Second, to minimize the heat gain or loss from windows, historic buildings often included interior or exterior shutters, interior venetian blinds, curtains and drapes, or exterior awnings.”
Given how many buildings have too much glazing, much of which isn’t operable or effectively shaded, it seems like our forefathers had some pretty good ideas about how to build right.