Yesterday I talked about what needs to be done before adding insulation to your attic - seal bypasses! Today I have several photos of bypasses that I find in attics every day. These bypasses cause serious problems with attics, but a lot of people just don't understand this. Bypasses cause frost and ice dams, and they need to be corrected before adding insulation to attics.
This photo shows a bypass to the attic space around a furnace flue. The square piece of metal is not sealed to the drywall, and there is a fair amount of air leaking into the attic space from this gap. I brushed the insulation away to show the gap for the photo. The insulation has turned black because of the air leakage - as the warm air passes through the insulation, the fiberglass acts like a filter and collects the dust / dirt particles in the air. Any time you see darkened insulation, you can bet there is air leakage occuring. The black insulation is often confused with mold because it looks similar.
This photo shows several holes that wires pass through to get to the attic. These holes could easily be sealed up with expanding foam. I didn't move any insulation to find these holes - this is exactly how the insulation looked when I climbed in to the attic, so there is obviously missing insulation here too. The recommended insulation depth for loose fill fiberglass is 18", but the silver areas have no insulation at all.
There is a major attic bypass around this furnace flue, and this is one of the most common bypasses that I find. You can clearly see the walls on the floor below, and you can even see the basement ceiling from this opening! To correct this bypass, the owner will need to install a large piece of wood, metal, drywall, or any other material that air won't pass through, and caulk all of the joints to make it airtight. This wasn't obvious just by looking, but I always make a point of pulling the insulation away from furnace flues to look for bypasses. The fiberglass batt on the right side of the photo was sitting on top of this opening.
Hopefully these photos have helped to illustrate exactly what attic bypasses are and how to correct some of the issues.
Reuben Saltzman, Structure Tech Home Inspections