One of the keys to minimizing the transfer of heat through your home’s attic is to completely seal the attic. In addition to covering the floor of the attic with a thick blanket of fiberglass insulation, there are a few special situations to handle as described here that will reduce your energy bill .

What’s the big deal about a few leaks?

Surprisingly, it takes only a one-percent gap in the insulation of your attic to significantly lower the net R-value of the blanket of insulation. For example, a total of 3 ft by 4 ft of uninsulated openings in a 1,000 sq ft R-38 attic blanket— just a one-tenth-inch gap between insulation and ceiling joists for the average home, or an uninsulated attic access door—lowers the R-value for the whole attic to only 26. In this case, you paid for R-38 but only got R-26, and your energy bill will reflect that. The solution is to install insulated coverings for these gaps.

Light-Fixtures

Ceiling light fixtures and ceiling fans are hooked to electrical boxes for support and to protect wiring connections. The boxes often have gaps around their openings, and the back of the box is usually uninsulated. These gaps represent an opportunity for air leakage.

Recessed lights in your ceiling generate heat that can be a fire hazard if in contact with attic insulation. The industry has solved this problem by using special light enclosures called “Insulation-Contact” (IC) cans with double metal shells to prevent such direct contact. If your light fixture cans are not IC-rated, they must be prevented from contact with insulation during installation. Many builders install boxes made of foil-covered material that isolate non-IC-rated light cans. After the installation, the lids of the boxes are removed to allow heat from the light cans to escape through the insulation blanket.

Vent Pockets

A typical ceiling has a number of penetrations: pipes, vents, ducts, wires, etc. For some of these, like pipes and wires, it is all right if they are covered completely with blown-in fiberglass insulation. These penetrations should be completely sealed with foam prior to installing insulation. However, some, like bathroom and kitchen ventilation ducts (or vents,) cannot be buried in insulation; they simply must exhaust air into the attic. It is important to install moisture-resistant boxes with closed tops, called “vent pockets,” over the end of the vent prior to blowing attic insulation. The top is removed later to allow the exhaust to escape. Unfortunately, these vents are air leaks, but they can’t be eliminated.

Access Doors

Many people use their attic as a storage space, or for other reasons, for which they need occasional access, so there must be an opening to the attic. These openings can transfer heat to or from the attic, particularly if this attic access is located in a designated heating/cooling zone. You should install an insulated covering for access doors that improves the insulation factor of the door. This means the attic of our example would retain its R-38 insulation capability.

The result?

Remember that leaks are energy wasters. If these and other penetrations are sealed prior to installing insulation, you can save on your energy bill.