Attic And Loft Insulation

What this is

A loft is the easiest part of most houses to insulate well, because the surface is reachable and nothing needs to be taken apart. In an unheated loft the insulation belongs at the ceiling line, between and then across the joists. In a loft that has been converted into a room, the insulation instead follows the slope of the roof, which is a different and much more involved job.

Telling whether your home needs it

Go up and look. If you can see the tops of the joists standing proud, the layer is thin. If the insulation is flattened, gappy, or stops short at the eaves and around the hatch, it is not doing what it should. Frost or snow melting off one roof slope noticeably faster than a neighbouring one is another sign that heat is escaping through it.

What the job involves

The first layer goes between the joists, cut to a firm friction fit with no gaps at the ends. The second layer runs across the joists at right angles so the timber itself is covered, since bare joists are a straight path for heat. Boards for storage must sit on raised battens so the insulation is never squashed; compressed insulation loses most of its value.

Things to watch

Keep a clear ventilation path at the eaves so air can still move under the roof covering, and hold insulation back from the edge with rigid trays if it wants to slump into that gap. Do not insulate underneath a cold water tank, because it relies on warmth from below to keep from freezing; insulate its sides and lid instead. Leave a gap around recessed downlights unless the fittings are rated to be covered.