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Attic & Roof Insulation

"To have a good roof over one’s head": this very expression says how important this part of your home is!

It is a well-known fact that heat rises, and your roof – the barrier between you and the open sky – is what prevents it from escaping. Therefore, it must be as airtight as possible!

Today, most regular-sloped roofs on new homes are insulated with blown cellulose. The preparation is straightforward, and – when properly done – this type of insulation is very effective. Roofs with more complex geometric configurations pose certain challenges to ventilation. In these situations, it is recommended that you seek an expert’s advice.

Some roofs have various sections, at various heights: The important thing to remember is that sections that are directly exposed to inside heat must be well insulated!

In all cases, the guideline is simple: the temperature must be the same on both sides – inside and outside – of the roofspace.

Inadequate ventilation or insulation in the attic can cause icicles and shorten the lifespan of the roof.

Insulation model

Given the importance of the roof, make sure you use the right materials:

  • A vapour barrier (polyethylene – 6 mm) with an overlap
  • An acoustic sealant
  • Wind baffles (venting chutes/rafter vents) on the far end of the ribbon strip to eliminate thermal bridges*
  • Cellulose

(*It goes without saying that each element must be correctly installed.)

To create a hermetic seal, we recommend using urethane for cathedral ceilings and tight spaces.

Isolation Majeau recommends

Precautionary measures

For proper roof insulation, make sure that:

  • The plumbing vents are well sealed off
  • The roof hatch is well sealed and insulated
  • The soffits are not blocked
  • The casings of recessed lighting fixtures are compliant and adequately insulated (light bulbs are a heat source that can cause condensation problems)
  • The central fireplace, if there is one, is equipped with a housing and discharge system (radiant heat)
  • The ventilation is adequate

Wall-roof joints and skylights

Special attention must be paid to the joints between the exterior walls and the roof. Skylights represent a particular challenge: they must be perfectly sealed and insulated to avoid moisture and condensation problems.

Cathedral ceilings

Cathedral ceilings are popular these days, and they are frequently insulated with fiberglass batts. Because there is usually space between the insulation and the roof trusses, however, there is an increased risk of creating thermal bridges. Urethane is more appropriate: it not only seals off the roof but also helps strengthen the structure.

More expert advice

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