As a custom home builder in the high-end market for the past 20-plus years, I have watched the emphasis on energy efficient building practices grow to the point where a blower door and tape roller have become as standard in the toolkit as a block plane and a circular saw. On every house we build, we have been engaging in rigorous taping and sealing procedures –from the foundation through the roof — to great effect, and often achieving ACH50 (a measure of how much air leaks per hour) numbers well below 1. However from a cost-per-square foot basis on a complex project, these wins often come with a significant price. These numbers often prove very difficult to achieve, even when code dictates that they must be reached and verified. To that end, we are constantly searching for new products and practices to streamline the air-sealing process and achieve our results with less cost and a knowable result.
The Solution – AeroBarrier™
Aerobarrier™ is an aerosol air sealing system we recently added to our toolkit to try and address these issues. In essence, the system involves blower door pressurization of the house (to +100 Pascals), a series of tripods with spray nozzles on them and the introduction of a fine mist of specialized acrylic caulk. From there, much like a balloon with pin holes in it, the pressure drives the sealant to all the small cracks in the building and seals them up. During installation, we monitor the air changes per hour on our screen and watch the needle drop as the various holes and cracks throughout the house fill with sealant. When we reach our leakage target we turn off the machine, clear the air with a few fans and open windows and clean up. In most situations, we can take a house from around 7 ACH50 down to below 1 in under two hours of spraying, with set up and clean up on either end amounting to another few hours. The space can be worked in again within about thirty minutes, and once cured, the sealant is a non-toxic, low-VOC substance that is GreenGuard Gold certified for use in schools and hospitals.
We can install at two different points in the building process: 1) Up against the exterior sheathing plane, after all mechanical penetrations are complete. In this case, it is important that there be insulation applied to the exterior of the sheathing, in order to keep the wall-assembly dew point away from the air barrier. 2) Up against the sheetrock plane (after mudding and taping, before finish paint). This method sometimes requires more protection before spraying (see figure) but ensures that the air barrier is as far away from the dew point as possible. This method is also used in multi-family projects, as it ensures air-space separation between units.
AeroBarrier™ will, in principle, fill a hole of any size given unlimited time and material, but in practice, it is limited to gaps of around 1/2” or less in width. The product does not stick to any vertical surfaces, but it will adhere to horizontal ones. So, while window sills and sashes are easily covered with tape before spraying, finished floors, counter tops, appliances etc. require protective covering. From a cost perspective, AeroBarrier is usually about $1.50-$2.00 per square foot of floor to install.
In general, this system has changed the way we approach air-sealing and could change the way we think of insulation practices. However, it is not an all-in-one approach to good building practices. We continue to take care to keep our sheathing planes continuous, gasket or spray foam building penetrations and in general build our houses tightly and soundly. What we have moved away from is excessive use of tapes, wraps, and sealants for air-sealing, freeing up more of our time to be carpenters and craftspeople.
Next issue, we will share some local stories about projects sealed with the AeroBarrier™ system, as we learn about this amazing new innovation that is transforming the way to achieve airtight high performance construction.
Sean Flynn is the owner of Silver Maple Construction in Middlebury VT. His company specializes in super energy-efficient, high-end custom homes and unique commercial projects. He lives with his wife and three young boys in Weybridge VT.