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Huh? Blasphemy. Yeah, well, in some assemblies, it is actually a pretty good idea. The most famous "double vapor barrier" of them all is a classic compact flat roof. Check out Figure 1. The roof… Read More

A wall is supposed to keep the outside out and the inside in. That is the way things are supposed to work. Check out the “perfect wall” (Figure 1). We have our water control layer, our air control… Read More

With the “perfect wall” we were here way back when (BSI-001: The Perfect Wall). The perfect wall has four control layers outside of the structure:a water control layeran air control layera vapor… Read More

Maybe not. For years I have said that dog won’t hunt1. I have come around. The engineer in me likes tools. I can’t help it – it is a genetic defect we engineers are born with. With therapy we… Read More

Sometimes the obvious is not so obvious. And sometimes the not so obvious becomes obvious. For example installing leaky ductwork1 in a vented attic is a pretty dumb idea (Figure 1). It leads to… Read More

We have long wrapped our framed buildings with a “layer”. What we called it and what we make it out of has changed over time. And now the vapor permeance of it needs to be re-thought. How low can you… Read More

Vitruvius had it right 2,000 years ago: “…if a wall is in a state of dampness all over, construct a second thin wall a little way from it…at a distance suited to the circumstances…with vents to the… Read More

Sometimes we make easy things hard. And sometimes we make hard things easy. With continuous insulation and punched openings both things are true.The physics is easy. A wall has to control water, air… Read More

Things have evolved considerably since the Eisenhower and Diefenbaker years. Hutcheon2 taught us about air flow that decade but it took more than a half century to get it right. We needed air control… Read More

For all that we know about roofs–which is a great deal–sometimes things can get confusing. I am more than partly to blame for that. I wrote a lot of the code language dealing with both vented and… Read More