We learn from an early age how important walls are. From fables like The Three Little Pigs to building towers with our blocks, we learn pretty quickly how important the walls can be. As we get older, we don’t always think about these powerful structures in our daily life, but we sure are grateful when they do their job! In the world of Passive House design, the walls do an even bigger job and it’s why we think about walls a lot around here at the AE Building Systems team, especially when it comes to making sure they operate well!
We pulled together our top rules of thumb for smart wall design that works FOR you and not against you in your goals to keep your home smart, sustainable, and standing for the long haul.
- Keep Air Out! Air carries moisture, so it’s a general rule to keep as much air out of the interior of your wall as possible. Air-tight design in wall assemblies helps protect walls from moisture and condensation building up inside the wall. As a result, you avoid a ton of headaches down the road!
- Walls should dry to the exterior. Anytime you can push moisture to go outside, do it! Get the vapor to dry to the exterior so that it can dry out and evaporate to the environment instead of inside the home. That’s because moisture moves to where it is dry and it is usually drier outside than it is inside. We cook, shower, breathe, etc. adding moisture to the interior of the home.
- Continuous Insulation is your friend! Continuous insulation (CI) helps move the dew point outside of your wall assembly. Put the thicker insulation, or higher r-value insulation, closer to the exterior. Some continuous insulation is vapor closed so be aware of the consequences of CI. Most foam products are not vapor-open. Some low-density EPS has a small perm rating and mineral wool boards are a great option when using a thinner layer of continuous insulation. Mineral wool has a fairly significant perm rating.
- Consider the climate. In Colorado, where the climate is more dry, you can sometimes get away with drying to the interior if it’s necessary. This works better when we are not actively humidifying the space.
- Zip-R Perm Rating. Zip-R homes have a thinner insulation layer and it does not move the dew point out of the wall assembly in much colder climates like Colorado’s. Zip-R sheathing is a simple all-in-one structural panel with built-in exterior insulation with integrated moisture, air, and thermal protection. Zip-R is a somewhat newer product so the jury is still out on how these walls hold up.
Do Walls Breathe?
Rot, mold, and all sorts of fun stuff can build up when moisture gets inside our walls. As a result, air tightness is critical for your wall assembly and you can never get your walls too tight. Walls do not need to breathe. They need to be vapor open to allow moisture to escape. Not only that, but energy loss and interior comfort levels are directly affected by your wall construction.
We actually can learn a lot from a cactus when it comes to moisture and wall assemblies. The cactus “skin” has essentially two perm ratings. The cactus absorbs vapor through its skin at night, and in the daytime when temperatures rise, that same skin prevents the moisture from escaping. The skin of the cactus allows moisture to migrate inward, but not outward.
SIGA has learned the answer to keeping walls dry by incorporating the unique characteristic of the skin of the cactus to collect and store water. In our buildings, we want the opposite to happen — prevent moisture from getting into our walls and allow it to migrate out. SIGA’s product, Majrex, does just that.
If you take these considerations into your wall construction, you’ll be going in the right direction. Of course, you can always geek out on this more and we love talking walls with our customers and partners! Talk to our team about how you can make your walls more tight and more effective!