TECH REPORT: Why We Need Better Walls

Do we really want better houses? A good place to start is with an understanding of why typical new home walls aren’t that great. Sounds ridiculous? I don’t think so, and there are two reasons why.

First, typical stud frame walls are sealed, mysterious places that homebuilders rarely see once the insulation goes in and the drywall goes up. Few homebuilders are in a good position to say how well these walls perform, despite the fact that some of them think they’re experts on energy performance. Second, I constantly run into builders who don’t understand building envelope dynamics in our cold climate, and the kind of trouble homeowners face when things go wrong. A real story from the winter of 2013/2014 is a case in point.

It all started when a homeowner decided to remove baseboard in preparation for a paint job on a second story room in a 9 1/2 year-old house. As soon as the trim was pried off, water started flowing out onto the floor from behind the wall. Not good. An immediate call to the insurance company and it was decided over the phone that the problem must be faulty vinyl siding. Sorry, no coverage. The alarmed homeowner pressed the point, the insurance company sent out a contractor to inspect, and the faulty siding diagnosis was confirmed, even though the siding was visibly perfect. Cost for repair: $10,000, no insurance coverage.

Somehow, the fact that no rain had fallen for weeks beforehand was lost on everyone but the homeowner who didn’t buy the feeble siding excuse. A building envelope specialist was called in. The real cause of the water? Condensation developing inside the code-built, inspector-approved wall during the ultra-cold, rain-free weeks. Solution? Strip everything back to bare studs, and rebuild the wall in a condensation proof way. Cost? Who knows.

I may be labeled as a heretic for saying this, but typical stud frame walls used across Canada are just barely adequate for the job, and I’m not talking just about R value here. The real issue is the way these walls are so prone to internal condensation if they’re not put together with a remarkable level of diligence. And the colder the weather gets, the closer to condensation disaster will come. And it all boils down to the fact that it’s possible for air to move through hollow walls.

Without some kind of functional vapor barrier on the warm side of hollow frame walls, every home would rot to the ground because of internal wall condensation. It would only take a few years, too. As warm indoor air permeates outwards through the wall assembly it cools during cold weather. Eventually this air cools to the point where it can no longer hold the moisture it carries. When this happens water droplets appear out of nowhere within the wall, and whenever water and wood meet, mold and rot inevitably follows.

The only thing that prevents this cycle of cooling, condensation and rot is the vapor barrier action of paper-thin polyethylene plastic and the painted and tape drywall that sits on top of it. Any flaw in this covering allows warm indoor air to sneak into wall cavities where moisture inevitably condenses. More flaws, more condensation. When a piecework construction crew is sloppy about vapor barrier installation (and it has happened!), problems like the winter surprise I just told you about happen. Are all situations usually this extreme? No, not all. But that doesn’t mean that smaller amounts of unseen condensation aren’t still causing damage. In fact, I believe it happens to some extent in most homes.

Even worse than all this is the widespread ignorance of the whole wall condensation dynamic. The under-sophisticated insurance phone person pointed the distressed homeowner to an expensive siding replacement job that wouldn’t have solve the problem, and so did the professional contractor who came in later.

So, what should builders do? Well, that depends on how seriously you (and they) take your interest in an actually living in a durable, mold-free home. It really comes down to conscience. The fact is, the risk of being held legally responsible for building walls that form internal condensation in cold weather is very small. The homeowner I told you about doesn’t have the slightest hope of being compensated for a situation that ultimately comes from bad design and never should’ve happened in the first place. Besides all the distress they’ve faced so far, they’ll also have to somehow find the money to pay a renovation bill that will easily rise to five figures.

Are there alternative wall options? Could homes be built better? Absolutely, and they will become more common as energy performance standards rise and homeowners become more sophisticated. The only question is when will most builders start using them?

Posted on February 28th, 2015

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