This post originally appeared on the Green Building Advisor website.
According to code, a garage is considered an accessory building when detached from a dwelling, and outside the conditioned envelope when attached to the dwelling structure. They don’t fall under the same energy code requirements as a dwelling. That being said, it’s common in my market for both attached and detached garages to have some sort of heat source (I live in a very cold climate). If you are going through the trouble and expense of conditioning a garage, it’s probably wise to also think about its efficiency, both insulation and air sealing.
One of the big challenges for a garage is the overhead door, a door that completely relies on a gasket system for an airtight assembly. Traditionally, the air and water seal for an overhead door has been provided by a vinyl seal fastened to the exterior of the door frame and head. The seal is in direct contact with the overhead door when the door is closed. If the door has been properly adjusted and the seal has been installed in the right position, this somewhat works to limit air movement around the door. The problem is that often the door is not adjusted correctly or has moved out of adjustment as it cycles up and down. I’ve also seen where rodents have eaten through the bottom of the vinyl seal to gain access to the garage.
In my climate, it’s not uncommon to see damage caused by air leaking around the overhead door, especially at the top. The photo shows mold growth above the garage door. This garage has an exhaust fan that operates when a certain humidity level is reached. When the humidity inside the heated garage reaches a certain level, or if the fan detects an elevated level of carbon monoxide, the fan starts. An exhaust only ventilation strategy. The space around the overhead door becomes the makeup air location. During the heating season, this cools the surfaces around the door, they become wetter, and mold grows. There are a couple ways to combat this, first, use a product above and around the interior side of the garage door that does not mold, something like metal, vinyl or PVC. Second, improve the air tightness of the door.
There is an optional garage door seal that has made its way from the commercial overhead door market into the residential market, it is called the reverse angle garage door seal. It works in conjunction with the traditional vinyl seal fastened on the exterior. This seal is attached to the overhead door sidetrack and contacts the overhead door sections, providing a second seal.
There are a couple requirements to install the reverse angle garage door seal, the first is the rough opening for the garage door needs to be 2 inches narrower and 1 inch shorter than the actual overhead door. The seal also requires a special sidetrack. The traditional track is held in place by brackets spaced every couple feet or so. The reverse angel seal needs to have a continuous track along the edge for attachment of the seal.
There is also a reverse angel seal for the top, this seal attaches to the top of the door instead of the door track. This optional seal can be added to most overhead doors without any special needs except for the one-inch reduction in the overall height of the overhead door rough opening.
I had a conversation with an overhead door installation company in my area about the reverse angle garage door seal. They said the seal can be added to any new door at a flat fee of $200. Adding this option to an existing overhead door will increase costs.
Do they work? Well, they were used on the overhead doors at my recent barndominium project. There are three overhead doors in total, 1-8×8, 1-10×10 and 1-14×14. That’s a lot of potential air leakage around a door’s perimeter. The entire structure tested at .38 ACH50, and .038 CFM/square foot of surface area. We were unable to detect any air leaking around the overhead doors. I’m sure there were some, but we weren’t able to find any.
Air sealing a garage leads to other considerations. Managing water and humidity, especially in my climate when snowy, ice covered, and very cold vehicles enter a heated space. Addressing a potential air quality issue when the garage is attached to the home is also a concern. There are a lot of details that need to be thought through with garages, improving the air seal around a garage door is only one. You can find more information about attached, conditioned garages in this Fine HomeBuilding article: