Insulating an attic

11.08.2008 03:00 Home - Source: Home Envy

Every so often you should try being away overnight somewhere, especially if there's a chance that a relative will decide to add insulation to the attic while you're gone. Here are some motivational incentives for you and the relative:

• Up to 45 percent of a home's energy loss is through the roof. If you're paying through the nose for heat, and half of it is escaping through the roof, that's annoying.
• If you live in a colder climate, your attic should be insulated with a value of R49, which is roughly 16 inches of fibreglass insulation, or 12 inches of cellulose (the loose stuff that's usually blown in).
• Many Canadian attics are heat suckers. Quite a few have only have 3 inches of insulation. Ours, according to dramatic testimony from my relative, was actually bare in spots. Bare. Especially over the entire master bathroom. This explains why, when it's minus 30 degrees outside, the highest attainable temperature of bath water is semi-solid.

Up on the Roof

Roofs are part of a slick system. The goal is to keep a home's roof the same temperature as the exterior air. In cold climates, this means preventing warm air from seeping into the attic from the house below, thereby heating the roof, and turning snow into icicles and ice dams on the eaves.

So first you need to stop warm interior air from rising up to the roof. Hence the need for a thick, insulating blanket of fibreglass or cellulose to keep the warmth in the lower part of the house and the cold air in the attic where it belongs.

The second thing you need is attic ventilation. If you don't have proper ventilation, warm, moist air from the house comes into contact with the cold attic roof and rafters. Condensation forms and accumulates, leading to rotting roof members and expensive repairs.

Good attic ventilation gets rid of that moisture so that air circulates freely, carrying off moisture (in winter) and unwanted heat (in summer) through vents in the roof ridge, eaves and gables.

Pretty in Pink

Adding fibreglass insulation to your attic is a great way to ensure that the attic temperature is distinct from the temperature in your living spaces. It's a relatively easy job, but prickly.

First, measure the thickness of the existing insulation. Then calculate how many additional inches you need to attain the correct R-value for your climate. Every inch of fibreglass insulation gives you 3 units of R-value.

Here are some tips for upgrading your insulation with fibreglass batts:

• Buy enough un-faced fibreglass insulation (i.e. without a vapour barrier) to cover the dimensions of the existing attic. If your attic is too cramped to measure accurately, measure the square footage of the rooms below instead.
• Insulation is sold in bundles of various thicknesses. The retailer can tell you the square footage covered by each bundle. The bundles are bulky. Unless you've got a truck, have the insulation delivered.
• Wear a dust mask, eye protection and heavy clothing with no skin showing or you'll be itching for days. If you have sensitive skin, have someone tape your gloves to your sleeves. Go to the bathroom first.

Additional tips

• Fibreglass sheds. Put drop cloths over furniture and floors.
• Get a second person to help shove the bundles or individual batts into the attic.
• Once you're in the attic, hang a temporary work light and put planks down across the joists so you can walk easily. Be EXTREMELY careful not to step between the joists. The drywall or plaster won't hold you.
• Start laying batts at the outer edge of the attic and work towards the attic access.
• Lay the batts perpendicular to the joists over existing insulation.
• Butt the lengths of insulation together tightly for a complete barrier to heat flow.
• Cut batts to size on a board using a very sharp kitchen knife.
• Do not let insulation touch flue vents or eave vents.
• Never cover wiring or recessed light fixtures with insulation. Leave 3 inches of space around them.

Note

The first layer of insulation should always have a vapour barrier. So if you're installing insulation in an un-insulated building (like a cabin or cottage) you must buy batts with a vapour barrier, and install them with the vapour barrier facing the interior of the house.

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