Posted by: SherlockHomesSY | 28 Jan 2011

51 Holes: Air Sealing Attic Ceilings

DIY Air Sealing & Insulation Guide

Click to DIY Air Sealing & Insulation Guide


– Attic Stairs & Scuttle Hole
– Recessed Can Lights
– Electrical Outlets
– Duct Registers
– Exhaust Fans
– Flue Vents
– Walls, Cables, & Pipes
– Chases
– Soffits
– Attic Doors
– Foamed Roofline

Over Christmas 2010, I had a delightful time with my sister.  She bought a new house, and I was dying to check it out as the best present I could ever give her.  I spent all kinds of hours going over it, laughing and trying out all kinds of kool new things I just learned along the way. She had a gremlin and I named it, while providing a full dossier: DUST!

I laughed inwardly as she described how her ghost behaved and where she thought it came from.  A few years back, I would’ve concluded the same thing.  But, I seen this spirit before and it took me a long time figure it out.  After over a 1000 houses, I sorted this one out,  especially when families called me in to discover it from them.

As odd as it seems, a house becomes incredibly dusty when walls and floors are tightly sealed and the attic ceiling isn’t.  I can usually spot the gremlin right away because I can see its signature on a return grill.  It’s usually black, with dust bunnies all over it and all around the sides.

I’ll never forget the day I finally trapped the creature.  I stood at the top of attic stairs in a garage and nearly got sucked out roof vents because air was pulling that hard.  For once I was cool in a hot attic.  The attic was trying so hard to let heat out that it was drawing air in as hard as it could.  It was like trying to suck through a straw pinched tight.  The attic and the air return were sucking so hard that it was pulling dust, and whatever else is in the attic, through holes in the ceiling and into the heating & cooling system, in addition to wherever else cooler air could escape.

When I counted all the holes in my sister’s ceiling, I found 51 holes in the main attic.  There were 4 others in the other one.  This series is about how to air seal those holes and others she doesn’t have. thankfully.

It’s appropriate to start here because my first recommendation for just about every house is stop airflow from the house through the attic.  Slowing air movement due to the stack effect solves a lot of problems.  It also creates a few that have to be dealt with too as a result—like adding mechanical fresh air ventilation and ensuring smoke exhausts properly.  If there is only one thing you can do for whatever reason, seal the attic ceiling.

Described here are types of holes we’re about to talk about air sealing.

Attic Stairs & Scuttle Hole. The hole in the ceiling allowing access to the attic is the biggest single open hole in the house.  It also looses the most heat.  Not only does it leak air, it’s usually not very well insulated—if at all.  It usually lowers the insulation value of the entire attic by ~25%.

Recessed Can Lights. Taken together, down lights are probably the second largest hole in the attic.  The old steel ones leak like a sieve and insulation has to kept away—also leaving “a lot” of the attic uninsulated. Even the newest ones, the aluminum air tight ones have air leakage problems.

Electrical Outlets. Except house for houses built in the 1970s, when swag lamps were popular, the most common hole in the ceiling is electrical outlets.  They’re usually for lights and smoke alarms.

Duct Registers. When someone decided the heating and cooling systems should be installed in the attic, it meant at least supply ducts are routed through the attic ceiling too.  They’re good for about a 3 square inch hole each.

Exhaust Fans. Starting in the 1970s, we started air sealing the houses.  When we did, we started tightening up our houses and then needed a way to get pent up moisture out.  Now we have bath area fans through every bath room and toilet room ceiling.  In one story houses, the rangehood fan from the kitchen usually goes through it too.

Flue Vents. If there are gas appliances, the flue vent goes through the ceiling also—unless the appliance happens to be the high-efficiency kind.  Like recessed can lights, they get hot and require special treatment to avoid fire.

Walls, Cables, & Pipes. The most obvious, yet least recognized hole the attic is the top of walls.  It’s where drywall is attached to studs—without caulk or other sealant.  Nobody likes seeing pipe and cables, so they’re hidden in walls.  Sometimes they’re routed out of the top of the wall and through the attic.  Air lost through these holes is felt around receptacles and light switches.

Chases. Sometimes, big pipes, such as ducts, go through hidden cavities (chases).  I’ve seen some really big ones.  Besides loosing incredible amounts of heat because their uninsulated, some allow a lot of air movement—especially when the bottom end is in the crawlspace.

Soffits. To give the house some architectural appeal, sometimes there are changes in ceiling height.  Some of them come in the form of soffits around cabinets, ducts, or lights.  Not only are they missing insulation, some have some pretty big air pathways through them.

Attic Doors. Most attics aren’t heated or cooled, but for whatever reason, the attic doors are installed like an interior closet door.  A full-size door has about a 29 square inch hole around the frame, where the door fits.  Not only that, interior doors have almost no insulation value: around R-1—if that much.

Foamed Roofline. Sealing all the holes may take some time.  If you’re not a do-it-yourselfer and have a lot of holes,  it could run a modest amount of money to plug them up.  In this case, it may be worth leaving them all there and air sealing the roof deck instead.  The heat load on your heating and air system will go down considerably too.


Air sealing is the most cost effective thing that can be done to improve energy-efficiency, comfort, and health.  Air sealing the attic ceiling, in my opinion, the best single thing you can do.

I started with the US Environment Protection Agency’s (EPA’s) pamphlet on Do-It-Yourself Air Sealing and Insulation.  To learn how we diagnose and correct air leakage, see our home performance website.  Before you start, be sure to head our warning in this blog’s second post: Air Sealing.

In Conclusion

In our next post, we’ll start this series.  The ones my sister needs will be written first, so she can beat her dust problem for good.  Air sealing and insulating the attic entrance is first!


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