Pretty easy…just connect the water control layer of the roof, wall and foundation to each other…the air control layer of the roof, wall and foundation to each other…vapor control layer of the roof, wall and foundations to each other…and the thermal control layer of the roof, wall and foundations to each other. Then it gets complicated…punched openings like windows and doors… It gets worse…decks...
This is most important of all the laws of thermodynamics….
Of course the crazy way we speak about the Second Law does not help: “In an isolated system, a process can occur only if it increases the total entropy of the system.” Huh? It makes you want to hate Rudolf Clausius. Couldn’t he just say that heat goes from warm to cold?1 Most of us get the heat goes from warm to cold thing. It’s the other simple applications of the Second Law that we miss:
• moisture goes from warm to cold
• moisture goes from more to less
Can it be so easy that all we have to do to make the perfect wall more perfect is leave out the vapor control layer and allow the all to dry in both directions? Ah man, why do you ask these types of questions? Go irritate someone else. The answer is yes. Sorta. Kinda. But not always.
So where are we after a half century? We went from the interior to the exterior with air barriers. And we went from combining the vapor barrier with the air barrier on the inside to combining the water control layer with the air barrier on the outside. We went from films on the inside to sheet goods on the inside. Then we went from films on the outside to sheet goods on the outside. We went from caulking and the black death on the inside to tapes and fluid applied joint systems on the outside. We are not done of course. But we are well on the way.
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.
How can you take a system with thousands of years of history and screw it up? Easy. Keep improving it until it does not work. Babylonians used it. Egyptians used it.
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.
One moisture transport mechanism that is often overlooked in building construction is capillarity or capillary suction. Capillary suction acts primarily to move moisture into porous materials. For example, a paper towel, with one end in contact with liquid water, draws water into itself against the force of gravity as a result of capillary suction.
It is pretty weird to dig a big hole and drop a building into it. A one story house with a basement is really a two story house that you dropped into the ground burying one story. Think about it…now you have to make the part in the ground strong enough to keep the dirt out. Even more difficult you have to keep the water out. Oh yeah, you also have to keep the soil gas out. It is kind of dumb to try to install windows. What are you going to look at? Worms? So you surround the windows with vertical shafts in an attempt to connect them to dayligh
The basis of the current ongoing Canadian Civil War between pressure equalization and ventilated and drained claddings (open-joint cladding systems). Old school engineers like me were taught by Old Masters like Handegord who pointed out that drainage was the key to life in general and pressure equalization—if it applied at all—was for joints and not for entire wall assemblies. Claddings were to be drained. Ventilated if you must, but first and foremost they had to be drained.