It has long been known that without making your home air tight, there is no way for your insulation to perform at it true r value. For example if your walls are built with 2 X 6 studs and insulated with R-21 insulation batts, without the house being airtight, the insulation performs at a reduced R value, something around a R-17. This is caused by gaps between the studs and the insulation which allow air to leak by. The problem in the past with making a home air tight was that the process would also trap moisture in the walls, which would lead to dry rot. Back in the 80′s and early 90′s air tightness was tried by installing 6 mil. plastic on the studs and drywalling over it. With plywood or OSB on the exterior of the wall, this left no place for the water to escape. I remember walking into houses before the drywall was installed and watching the water run down the sheets of plastic. This method of air sealing was quickly dropped and no real alternative was offered. Some minor air sealing of the bottom wall plate to the floor with caulk and foaming around doors and windows is about as far as we’ve gotten with the codes.
Just this year Washington state has adopted a stricter insulation code. It is basically the old Energy Star standards. One part of the code is the requirement that all new home have a blower door test prior to final inspection. Blower door test measures the amount of air leaks a home has. New homes are required to have a blower door score of 7.5 or lower. What this means is that if the air pressure difference between the outdoors and the inside of your house is 50 pascals (50 pound per square inch) then the air in your house will completely exchange itself seven and one half times in an hour. This is still a drafty house but its a start.
By making homes airtight we obviously can cut down the cost of heating these homes. Done correctly we also can build the walls in a manor that will allow moisture to escape. This is the best way to build. In future articles I will talk more about the methods behind this type of construction