A mantra here is that "the greenest building is the one already standing." There have been far too many posts about the loss of yet another Paul Rudolph house or the razing of yet another brutalist classic. Often it is claimed that modern buildings are energy sinkholes and are impossible to modernize.
The original Passivhaus standard was designed for new construction, with siting and sun angles being an important consideration. You can't do much about that in a renovation, so a special standard, EnerPHit, was developed by the German Passivhaus Institute. It calls for a reduction in thermal bridges, improved air tightness, high quality windows and a LOT of insulation, resulting in energy savings of between 75 and 90%.
Poured concrete buildings are essentially one giant thermal bridge, and about the only way to achieve such goals is to wrap the whole thing in insulation, from the footings up (10 inches of the stuff in this case). This would horrify historic preservationists as it can change the character of the house considerably. However care has been taken to maintain the form and the window openings, and the house has not been changed beyond recongition.
On the plus side, it's now comfortable and warm in winter, cool in summer, with almost no heating or cooling needed at all. The original concrete provides thermal mass that helps regulate the temperature. There are also solar thermal panels on the roof that collect hot water for domestic uses and radiant underfloor heating, via a tank in the basement. Mcdonald explains on a sunny day:
I use the sun like a reptile on a rock. Right now, the house is sucking it up. Later tonight it will ooze through the building.
The Greenest Insulation
If one is going to wrap a building in insulation, closed cell foams like styrofoam or polyurethane are often the first choice. But Doug Mcdonald has a "red list" of chemicals that he avoids, that includes halogenated flame retardants that TreeHugger has noted do not belong in green building. He solves this by using Foamglas, an insulation made from recycled glass that handles like styrofoam but is inert and doesn't burn. (See what architect Ken Levenson thinks about regular foams in Does Foam Insulation Belong in Green Buildings? 13 Reasons It Probably Doesn't.)
Alex Wilson of BuildingGreen called it his "favorite insulation material" and lists its virtues
There are no blowing agents that deplete ozone or contribute to global warming. There are no flame retardants or other additives needed to improve fire resistance. As a 100% inorganic material, Foamglas is inert and fireproof. And it has enough compressive strength to be used under any concrete slab--an application where extruded polystyrene (XPS) currently dominates the market. It's better than XPS, because, in addition to the absence of those chemicals, Foamglas is totally impervious to moisture (water and vapor), does not support mold growth, blocks radon, and keeps out termites and rodents.
It's also really expensive. Given that it is a building component that nobody sees and solves a flame retardant problem that few people care about, it is an admirable choice.
A thermal bridge too far?
As noted earlier, this renovation is not without its issues, ones that have to be faced by historic preservationists everywhere, about where we draw the line. Has this house been saved or changed beyond recognition? In this case, a careful renovation has preserved a house that otherwise might have been demolished as a drafty barn, by a designer who did his best to preserve as much of the character of the building as he could.
Do we really need to achieve Passivhaus levels of energy efficiency or would more modest goals be more appropriate for historic buildings? Doug Mcdonald has shown us what can be done; we all face a larger question of what should be done.
More information at MudaGreen