*Code Update*
Energy Efficiency Provisions for Building Thermal Envelope – House Wrap vs Air Barrier
Did I lose you already? I know, I know, not the most riveting post topic. But the idea is to inform you on the differences of the two and how the code update affects them. This year the question was posed to the North Carolina Energy Conservation Code committee “must house wrap material be rated as an air barrier material?” After some deliberation they have weighed in.
I try to aim my posts towards homebuyers/owners and their interests -without getting too technical. Admittedly, this post may be a bit technical. With that said, this is an overview of a very complex topic. We must understand (1) what they are, (2) how they act, and (3) how the committee updated the energy conservation code.
What Are They?
House wrap. Usually a synthetic rolled barrier between the house sheathing and the siding. It's used to prevent water or driven rain from entering the wall assembly. It also allows for moisture trapped, water vapor, in the wall assembly to pass to the exterior. Ex. Barricade or Tyvek. House wraps are often considered moisture barriers.
Air barrier. The ICC defines as "Materials assembled and joined together to provide a barrier to air leakage through the building." It may be a single material or combination of materials. Ex Drywall, insulation, and/or plywood with taped seams. House wrap CAN be Included in this category (keep reading). More specifically to be a good air barrier it must stop air flow, be continuous, and be durable.
How They Act
Things can get confusing since the names sound similar. Also, there are different names for these different components and which can perform more than one function. For example, House wrap by itself is not an air barrier, it is a vapor barrier. However, IF installed properly, which is rare, with taped seams, bottom, top edges, and no tears, it acts as an air barrier. So primarily it acts as a vapor barrier, but installed properly can do both; vapor barrier and air barrier.
To take it one level deeper, a contractor might use tarpaper (a moisture barrier) between his sheathing and siding, tape his plywood seam (air barrier), and utilize kraft-faced insulation (vapor barrier AND air barrier if properly installed), to help maximize energy efficiency and moisture control.
Code Update
The question that sparked this post was “does the 2018 NC Energy Conservation Code require that house wrap be rated as an air barrier material?” And the answer is NO. House wrap material does not need to be an air barrier, BUT the product used must be installed to manufacture specs (which most likely includes sealed joints and seams). Furthermore, the material itself is not affected by the NC Energy Conservation Code (as long as approved by NC Building Code and Residential Code), but the installation is.
A lot of technical stuff? Yes. But the bottom line is to make sure the builder of your future home knows and understands these distinctions. Many builders can build a house "to code", but knowing why and improving the end product is the kind of builder you deserve. Croatan Custom Homes strives to stay on the leading edge to deliver you a quality home that will be a sound investment for generations.