You Have a Hole in Your Ceiling The Size of a Basketball

Coin is about 1/16 thick.

A 1/16 of an inch crack is a mighty small crack. A 1/16 of an inch crack 12 1/2 inches long is not a small crack. Actually a 1/16 of an inch crack 12 1/2 inches long sucks.

How so and what does it suck? Let’s look at the latter first – it sucks conditioned air from your home.

Your ceiling is a component of what we call the building envelope. It helps form a barrier between conditioned air (inside your home) and unconditioned air (outside your home). If the crack is in your ceiling hot air in the attic can draw/suck cold conditioned air out. It happens through a natural principle of science call convection. Hot air rises. It makes hot air balloons fly.

Convection: the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.


Man cutting drywall.
Sheetrock hangers cut the hole larger than the box.

Consider a standard light fixture. It’s mounted to a box in your ceiling. The ceiling, most likely drywall, aka sheetrock, is installed by tradesmen called “hangers”. When drywall hangers install your sheetrock ceiling they cut holes to fit the box in your ceiling. They cut the holes to fit all the other penetrations in your ceiling (and walls).

Most ceiling boxes are round. Hangers typically cut the hole bigger than the box. The result is a tiny crack (hopefully it’s a tiny crack) about 1/16 inch wide around the circumference of the box. Unfortunately – most hangers leave much larger cracks.

Now, because we know that the length of the circumference of a circle is the diameter [in this case, 4 inches] x 3.14, a typical light fixture has a drywall crack that measures 1/16 inch wide and 12.5 inches long.

When you divide the crack and change the scale (perspective), this small crack looks totally different. Here are the equivalent sizes:

  • a 12.5 inch crack 1/16 of an inch wide is equivalent to a 6.25 inch crack 1/8 inch wide.
  • a 6.25 inch crack 1/8 inch wide is equivalent to a 3.125 inch crack 1/2 inch wide.
  • a 3.125 inch crack 1/2 inch wide is equivalent to 1.5 inch crack 1 inch wide.
  • a 1.5 inch crack 1″ wide is a hole a little larger than one square inch.

Walk around your home and count the number of penetrations in your building envelope. Count all the following and multiply by 1 sq inch.

  • recess can light fixtures
  • ceiling light fixtures
  • fans
  • air supply grills
  • smoke alarms
  • carbon monoxide detectors
Folding Stairs
Folding stairway to attic.

Let’s assume you have a three bedroom home built to current safety standards with hard wired smoke alarms, recessed can lights and a typical heating/cooling system located in your attic. We’ll also assume that your total penetration count is 40 (your home may have more or less).

Considering 40 penetrations with a 1/16 inch crack your home has an approximate 7 inch x 6 inch hole open to the attic. That is about the size of a kid’s soccer ball.

Now – if you also have a folding stairway located in the interior of your home and the crack around the doorway also measures 1/16 inch you have a hole about 4 inches x 4 inches in your ceiling. Add the air loss of the folding stairway to the other ceiling penetrations and you have a hole in your ceiling larger than the size of a basket ball.

Do the math and keep in mind – the above calculations are conservative. Also – keep in mind that we haven’t addressed the wall penetrations –  windows, doors, wall plugs and switches.

Grab a can of expandable foam, get in your attic or basement and seal those cracks. If you’re building a home – talk to your builder. Here’s a handy guide published by that may help with other energy loss issues.

Now – get cracking!

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