Wall details are small drawings sliced through a section of wall to show how walls, particularly exterior walls, will be constructed. Depending on the size and complexity of a project, an architect might have a dozen different types of walls that they need to show. In a residential project, there are typically only a couple of wall types. A good exterior wall should ideally have structure, control layers, insulation, cavity, and cladding.
Why do we need wall details?
Traditional 2x6 framed walls. They’re pretty much the default, but we can do better.
Different locations require different solutions. A wall in Alaska that has to insulate a home from -40°F temperatures and withstand snow building up along its base should look very different than a wall in California where earthquakes and fires are a concern, but the temperature is much more moderate.
Building technology is constantly changing. In the 15 years since I graduated college, we have gone from building cavity insulated walls with siding installed directly on top of building wrap, to understanding the benefits of using insulation on the outside of studs and utilizing rainscreen systems. And there are dozens of different materials that builders and architects can use in even the simplest exterior wall. It’s good to make sure that the contractor, subcontractors, architect, and homeowners are all on the same page by detailing everything.
The permit office wants to see them. Most places in the U.S. adhere to some edition of the International Residential Code, which has over 180 pages dedicated to proper wall construction. The city/county in charge of permitting wants to see that information in the drawings, and they’ll also inspect onsite to make sure that everything is installed correctly.
At this point, I get excited about walls & start lecturing. sorry about that.
A couple of my favorite 6” stud wall types to use in our climate are below:
I also really like Rockwool comfortboard in place of the EPS, especially in WUI zones. In that case, I’d relocate the building wrap!
In Boise, at the time I wrote this article, all residential projects need to have R20 or R13+5 insulation. R13+5 means that R13 is between the wall studs, with R5 on the OUTSIDE of the studs. You’ll notice that I’m a big fan of the R13+5 (or greater). Why? Wood studs are fairly thermally conductive! You can see this on many homes with cathedral ceilings (unvented roof structures) when it has snowed. There are melted stripes! That is warm air from inside the home leaking out through the studs. Between the studs is well-insulated, so the snow sticks. Wrapping wall studs with a layer of exterior insulation breaks that thermal bridge and insulates much better than only stuffing insulation between wall studs.
Image from heepsheap.wordpress.com - you can tell a lot about a building’s insulation by the snow melt patterns on the roof!
Ok, so what’s the deal with the air gap? That’s called a rainscreen. No building envelope is 100% waterproof – things like screw holes and joints in cladding (siding) are weak points where water can slip into the wall. Caulk is great, but it eventually fails. The rainscreen is a drainage plane directly behind the cladding that allows moisture to easily drain away from the building. The air that flows between the cladding and wall accelerates evaporation of any residual moisture. It’s a very efficient way to mitigate the risk of moisture intrusion and all of its unfortunate side-effects: things like musty odors, drywall discoloration, mold, and rot.
Rain drains freely down the wall & exits to the outside vs. capillary action into your house. It’s extra effort up front, but can save you money and headache in repairs later.
So make sure that your architect or builder is giving careful thought to your wall construction. Great construction is a little different today than it used to be. And if you’re the kind of person who finds this stuff interesting (my kind of nerd!), check out @buildingsciencefightclub on Instagram. She has great insights on why buildings fail, and how to build properly so they stay dry and warm.