Yesterday Landmark Services co-sponsored a symposium called "The Greenest Building is Already Built". It was meant to explore the relationship- good or bad- between sustainability and historic preservation. Five panelists provided wonderful presentations exploring the issues from divergent points of view.
Not surprisingly, there was almost universal agreement that preservation of historic buildings is "green" in that it: a) reduces the amount of debris tossed into landfills and b) it captures the embodied energy that it took to make, transport, and install the materials of which these buildings are made. Many pointed out, too, that present day designers could benefit by studying some of the features found in historic buildings, such as large overhangs to keep out the summer sun.
There was significant disagreement, however, between the preservationists in the room and those who advocate for "deep energy retrofits". A deep energy retrofit typically includes replacing the existing windows, and removing siding and exterior trim in order to install a layer or two of rigid foam insulation over the sheathing. Advocates pointed to the large energy savings (often 50%) and the potential for other benefits such as increased comfort and better indoor air quality. But preservationists decried the wholesale removal of original building fabric and did not like the impact that such a retrofit has on the exterior appearance.
My own view is somewhere in the middle. As a historic preservation contractor, I am obviously favor preserving original building material. However, I am also painfully aware that most existing housing stock is woefully under-insulated and this cannot be ignored as the availability and cost of fossil fuels becomes more unpredictable.
Would I advocate replacing original windows? No I usually would not. The arguments against window replacement are pretty clear. Restoring your original windows and adding a good quality storm window makes more sense financially, aesthetically, and environmentally.
Would I advocate for the removal of siding or roofing and installing rigid foam over the sheathing? Under certain conditions I probably would. If the siding and roofing were going to replaced anyway this approach might make sense if the new exterior siding and trim were detailed in such a way as to maintain the building's original appearance. The difficulty is that by adding 3-6" of foam on top of your roof, and 2-4" to your walls, you need to make the trim boards that much wider. It's tough to do this without creating an eyesore.
But for me it all depends on the significance of the building. I can see taking this approach on a straightforward 1930s Colonial, for example, but it almost certainly would be a mistake for most 18th and 19th century homes because a) these homes are fewer in number and therefore more significant and b) it would be difficult, if not impossible, to maintain the subtle architectural details that give these homes their beauty.
Our approach, here at Landmark Services, depends, of course, on the overall scope of the project and , more importantly, the goals of the clients. If a house is getting gutted anyway, it makes sense to insulate it as well as you can. We use either spray foam or dense packed cellulose because both methods stop most of the air movement through a wall or roof cavity. However on many of our projects we are opening up the walls in selected areas only, such as the kitchen or the bathrooms. In these houses we often just insulate those areas and the attic and leave the rest of the walls untouched unless one of the clients' goals is to reduce energy consumption as much as possible. Frankly, when it comes to old house renovations that is usually not the goal. Our clients want to reduce the energy efficiency and comfort, yes, but they want to maintain the look and character of their house as well.
For a more detailed look at my thoughts on insulating old houses download the paper that I wrote on the topic here.
By the way, the other co-sponsor of yesterday's symposium was a company called Terrene. They are a terrific resource for sustainable building materials such as cabinetry, counters, and flooring.