There are a lot of different ways to build a wall. There’s standard 2×4 walls, 2×6 walls, ICFs, SIPs, concrete block and steel stud, to name the major ones. Then, there’s what to put on the outside the wall (siding, brick, stone, EIFS, etc.), inside the wall (fiberglass, cellulose, spray foam, etc.), then the interior of the wall (what kind of sheetrock, paint, etc.). All of this is your wall system. Yes, the construction industry considers the wall system – not a living, breathing one – but a system nonetheless.
That said, the specific point of this entry is that caution needs to be used when using spray foam insulation & brick veneer in climate zone 4, which is where Wichita and Kansas City, to name a couple of cities, are located. Why? Well, it comes down to a few things:
- Brick veneer can store huge amounts of water.
- Most house wraps are also called a Weather Resistive Barrier, is very vapor permeable (as in water vapor goes through it very easily)
- The sun will drive water vapor towards the inside of the house, through the house wrap and into the OSB.
- The foam, open or closed cell, has such a low permeability that the water effective stops inside the OSB, as it has nowhere to go until it can evaporate back to the outside.
Unsurprisingly, this can lead to structural weakening of the OSB. So, what to do? The two main things to do involve tweaking common building practices slightly so that we can make longer lasting structure. Notice I’m not saying don’t do spray foam & brick veneer – I’m just saying that I would:
- Use a weather resistive barrier with lower permeability. Permeability is rated in Perms. Standard WRBs are 35 or so. 10 Perms or less will keep enough water vapor out to help minimize the intrusion.
- Change the way you build the veneer, to include more ventilation. Current practices on residential construction use only weep holes at the bottom of the brick at regular intervals. The research I’ve seen suggests that creating a more breathable brick veneer will keep moisture in the air moving & not heading in, towards your house.
Thanks to Lucas Hamilton at CertainTeed for doing all the heavily lifting with this. All I did was ask the question & thought I should pass along the information. And, again, this is just for Climate Zone 4 – and there are 6 across the U.S., so ask your builder, insulator, architect, energy auditor, what’s recommended for your area.