Preparing your attic for insulation

Lesson 2 of an informal online course: Home Energy 101.

by Philip Drader.

In this lesson, we’re going to talk about preparing your attic for insulation.

We know that hot air rises. In the winter, all winter long, moist warm air from your house rises up into the attic. There it cools and the moisture it carried up with it condenses out, leading to potential rot, or mould. It also melts the snow on your roof, leading to ice-dams. And you paid good money to heat that air up to do all that! If you want to stop the waste, you’ll want to insulate your attic.

Here’s a presentation I made about how to keep moisture out of your attic.

6 areas to draftproof before insulating your attic

Before you insulate your attic, you should draftproof all the penetrations into your attic.

There are 6 areas that may need to be addressed to prepare your attic for insulation. Here’s a quick video where I share five of them. The sixth area is knee walls in your attic.

1. Electrical boxes

Since your home’s drywall is considered an air barrier, it only leaks air at holes or edges such as electrical boxes like the ones on top of your light fixtures. They can be sealed with these three things, readily available at your hardware store:

• 6 mil poly (clear polyethylene sheeting that is 0.006 of an inch thick)
• acoustical sealant
• and staples. Construction staples and staplers are available also, but even a regular paper stapler will do the job. Note that it will get gunked up, but can be cleaned with mineral spirits.

Here’s how it’s done.

2. Wire penetrations and other holes

All holes coming into the attic, around pipes or wires for example, should get a good shot of foam to seal them. Talk to your hardware store about what you’re doing and the options available.

When you’re looking at the floor of the attic, you’ll see places where the interior walls are, with ceiling tiles or drywall on either side. All interior walls should have the drywall sealed to the 2×4, this works fairly well with foam if it’s a big gap, and caulk if it’s a small one.

It works perfectly well to have a contractor do this. Just make sure that these measures are in their scope of work.

3. Potlights

You’ll need to determine if any preparation is required if you have potlights that are installed in your attic for the floor below.

Look for a label that says if they are insulation contact (or IC) rated before you cover them with poly.

If they are not insulation contact rated, or you are not sure, you can cheaply build a drywall box to cover them (see video), which will also allow you to place insulation over the box without fear of fire or damage. A 3″ space around them is generally the minimum requirement.

4. Chimney

The next area to check is around your chimney if you have a working one.

You can draftproof around it, but you should not insulate it, in order to avoid overheating it. Your draftproofing materials will need to be fireproof, such as fire-rated caulking and steel sheetmetal.  A 4-piece metal flashing as shown here will help seal the chimney to the surrounding joists.

5. Attic hatch or door

The fifth area to prepare is your attic hatch or door. You should have a flexible weather stripping, and a tight fitting box.

For hatches in the ceiling, insulating the attic side is recommended.

6. Kneewalls

The last area you need to draft proof is the kneewall–that triangle of attic space on each side of the house. Air can travel between the finished room and the small attic space, between the joists. One of the easier ways is to cut some rigid insulation fairly loose for the space, then foam around the perimeter.

Scope of draft proofing work

Here is the quick list for a scope of work for draft proofing your attic before it is insulated:

1. Air sealing attic: cover all electrical boxes with 6 mil poly, sealed to drywall or stud with acoustical sealant, stapled in place
2. Seal all penetrations to attics by wires and pipes by foaming all around, into the hole if possible.
3. If potlights are IC-rated, treat as large electrical box. If potlights are not IC-rated, cover and seal with drywall boxes, ensuring a minimum of 3″ clearance on all sides.
4. Chimneys need to have firestopping insulation placed around them, and air-sealed with metal flashing
5. Attic hatches require flexible weather stripping to provide good air seal
6. Kneewalls, such as half-storey joist spaces, are to be blocked with rigid extruded insulation and foamed in place

Install moore vents

After you finish the draftproofing, you are ready for the next step to prepare your attic for insulation.

Moore vents (also called rafter vents or insulation baffles) are important to add so that air can vent from your soffit, through your attic, and out the roof vents. They are normally styrofoam as shown in photo on the right. They help carry away any moisture that may still be entering your attic. They are always needed if you are using blown in insulation to keep it from plugging up your soffits or getting moved by wind.

Manufacturers now recommend you use a moore vent between each rafter.

Now you’re ready for insulation

Now that you’ve done the hard work, you can get R50 blown into your attic for a fairly low fee.

Learn more

Natural Resources Canada – Keeping The Heat In Chapter 5: Roofs and attics