Can you tell an Air Leaks from Mold? Below are a few of the most common places you’ll find attic bypasses in just about every home in Toronto built before 1990. In all of the photos below, I’ve pulled the insulation away to reveal the bypasses; you wont find any of these in your attic without moving the insulation around. For the record, home inspection standards of practice don’t require the home inspector to move insulation so don’t be surprised if your home inspector didn’t mention any of this stuff.
Any time small cables or wires pass through the top plates of walls in to the attic, the holes for the wires should be sealed up. Whey they are not sealed, they leak air. Do you see how some of the insulation in the photo below has been darkened? It’s not mold. This is the result of years and years of air leaking through the insulation; the insulation acts like a filler, and traps all the dust in the air, turning black. Even though these tiny holes don’t seem like a big deal, having them all over your attic can have a huge effect. Sealing these gaps can be easy accomplished with a can of foam insulation. Larger penetrations in to the attic, such as plumbing vents, also need to be sealed. Again, foal in can works very well.
The first place to check for attic leaks is around the furnace vent; if there is air leaking into the attic around this chase way, there will surely be air leaking everywhere else. In this photo below, the darkened insulation is a dead giveaway that there is a lot of air leaking through here. Foam insulation wouldn’t be appropriate repair for this location – the vent is supposed to have at least one inch of clearance to anything combustible. In the photo below, installing a small block of wood to fill the gap at the bottom (maintaining a one inch clearance to the vent) and then sealing the entire assembly with high-temperature caulk would be a good fix. (See second row from the bottom vent is missing sheet-metal collar you could see right down to the walls after pulling the insulation away. This is very common in most houses.)
Here is a huge bypass around furnace vent; the chaseway that leads down to the basement was large enough for a person to fit through, and it was basically wide open at the attic; they just had a piece of fiberglass insulation covering the top. You can clearly see the basement ceiling from inside the attic.
The space around masonry chimneys will often a source of air leakage. I the chimney is being used for wood burning fireplace, there needs to be a two-inch gap to combustible materials. Sealing these air leaks will require the use of high temperature caulk and sheet metal. Whole-house attic fans can be a major source of air leaks in to the attics. These are fans that are designed to be run in the summer only. The photo below shows light leaking through the attic fan, which means a lot of air is leaking through as well.
Probably the largest attic bypass that commonly be found is the one above the stairway to the basement on old ramblers. All of the wall cavities are wide open to this space, and nothing is sealed off. This is a bypass that’s large enough to fit a small family into. Other ceilings drop down in older houses will be areas to look for bypasses – especially over bath tubs and kithen soffits. Finally, the space below the knee walls in old one-and -one half story house can be major source of air leakage. The way to repair this is to have solid blocking installed underneath every joist cavity, and have it made completely airtight.
For more information about home inspection QualitySpec Inc. 905-321-9882. Credits to Arshad Khan, Certified Home Inspector – P. Eng.