Vermiculite in older houses
In older houses, the attic may contain vermiculite, a grey-gold granular insulation. Vermiculite may contain asbestos. Do not touch it, and have it tested before any work.
Seal before you insulate
Insulation slows heat, but it does not stop air. Warm air from the house passes through loose-fill insulation with almost no resistance and carries its moisture along. That moisture ends up under the decking, where only attic ventilation can still carry it off.
Before adding insulation, the openings in the ceiling are sealed. That means the gaps around wires and pipes, electrical boxes, the tops of interior walls and the edge of the hatch. Air sealing is painstaking work for a contractor. It becomes almost impossible once new insulation is blown on top.
Blown-in insulation
In an open attic, the most common insulation is loose fill, blown in by machine. It comes mainly in two materials, cellulose made from treated recycled paper, and fibreglass. Cellulose is denser and slows air a little better. Fibreglass is lighter and handles moisture better.
Blown-in insulation has a clear advantage over batts. It fills the corners and covers the joists, which limits thermal bridges.
Baffles, where it all happens
The bottom of the roof is the trickiest spot. The space between the ceiling and the decking is thin there, and that is exactly where air from the soffits has to come in.
Blown-in insulation added without care slides into the soffits and blocks them. The attic then loses its air intakes. Air stops circulating, even if the roof has all the vents it needs.
Baffles solve this problem. These cardboard or plastic channels are fastened under the decking, between each pair of rafters. They hold back the insulation and keep a clear air channel above it.
The link with the roof
A well insulated, well sealed attic stays cold in winter. Less snow melts from below, and less ice forms at the roof edge. The decking stays dry. It does not turn black and does not go soft.
- Before a roof replacement. If the insulation needs redoing, tell us. The air intakes and exhausts can be adjusted to match.
- During a roof replacement. When the decking is open at the bottom of the slopes, baffles are easier to install from above.
Frequently asked questions
Should you insulate the attic before or after replacing the roof?
Either order works, as long as you put us in touch with the insulation contractor. If the roof needs redoing soon, use the job to have us install the baffles and fix the ventilation. The insulation can then be blown in without the risk of blocking the soffits.
Can you over-insulate an attic?
The thickness of the insulation is not the danger in an attic. The danger is insulating without sealing the ceiling, or blocking the air intakes. Thick insulation over a leaky ceiling keeps the attic colder and can increase frost under the decking.
Does insulation reduce ice dams?
Yes, insulation goes a long way toward reducing ice dams when it comes with an airtight ceiling and good ventilation. Heat lost through the roof is what melts the snow. The less heat escapes, the less ice forms at the edge.