Building Profiles: Retrofits

Things have evolved considerably since the Eisenhower and Diefenbaker years. Hutcheon taught us about air flow that decade but it took more than a half century to get it right. We needed air control. We needed an air control layer – an air barrier. We started off with locating it on the inside, moved it to the middle, and finally ended up with it on the outside3. We started by combining it with a vapor barrier on the inside then we finished by combining it with a weather resistive barrier (WRB) and continuous insulation on the outside.

We have learned to add holes and drainage in tall buildings in order for them to work. The lesson learned in tall buildings is that we can’t keep the rain out so we drain it out after it has entered. We can reduce the amount that enters but we can never completely keep it all out. Drainage and holes are key. These are regularly installed in tall buildings but not in short buildings. Until we add holes and drainage to small buildings they will continue to leak. This is so counter-intuitive that it borders on magic.

Air barriers have always been a big deal in flat roofs in cold miserable places like Canada even with black roofs. But back in the day you could get away without an air barrier in a flat roof in Washington, DC if the roof was black. Winters were not long enough or cold enough to cause problems and any moisture that did migrate upwards was driven downwards due to the extreme temperatures the black membranes would get to–above 180 degrees F.