In Perspective - Attic Doors
Harry Applin
607-659-4824 548 words
In doing a number of thermal imaging projects, one of the most noteworthy problems that leak heat from the homes is the attic door. Whether it is an actual door accessing the stairs to the attic, a pull-down stair or just an access cover, they all have been major leaks of heat into the attic space.
There are a couple of simple of facts that contribute to this problem. The first is called the stack effect. The stack effect is simply the application of physics within the house. The stack effect contributes to the cold drafts that are felt on floors. The simple physical principles are that heat rises and the air will find the easiest path to exit. That brings us to the second issue. Most attic accesses, whether a door or just a cover, are made up of wood. The R-value, the resistance to heat transfer, for wood is less than 1.5 per inch. The pull-down stair case access is usually made up off ½ plywood that has a R-value of less than .75. For a reference, the required insulation level for an attic in the building energy code is R-49, so the door is like having at least a six sq. ft. hole leaking warm air into the attic.
In an earlier article, I mentioned ice dams caused by heat being trapped in attic space and melting snow on the roof and it freezing at the overhangs. Leaks into the attic are the major cause and access is a large contributor to the problem. But there is an issue that I really haven't covered related to the stack effect. The stack effect draws air from the lower portions of a home and leaks it out the top of the house. That air usually comes from the basement and studies show that at least 20% of air leakage comes from the basement. Why is this important? Radon gas is one and cold air is the other. Most radon tests are done in the summer when the stack effect is at a minimum, but when there is a temperature difference between the outside air and the heated indoor air this changes considerably. There is now a low pressure drawing radon gas through cracks and openings in the basement and bring that gas into the living area.
The doors leading to the attic should be sealed with weatherstripping as if it were a front door leading outside. It is also possible to adhere a 1 or 2-inch insulation board onto the door to increase its R-value by between R-7 and R-14. It doesn't reach the R-49 but makes real improvement in the insulation value of the door. For the pull-down stairs and attic access covers, there are store-bought covers that start at less than $30.00 that run up to about $200. But for those that have the basic tools, building your own insulated cover is the way to go. I have included a website to give you ideas on building an access cover. Just remember that fiberglass insulation has a R-value of 3.4 per inch and insulated foam board insulation has a R-value between R-6 and R-7.
http://www.batticdoor.com/StairCover.htm