The pack count is easy. What decides whether the insulation works is whether it is fitted without gaps and without being squashed — and a small gap costs far more than the same fraction of thickness. Read that bit before you buy the thicker product.
Lofts, walls and floors. Enter the area, then the coverage stated on the pack.
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The pack count is easy. What decides whether insulation works is whether it is fitted without gaps and without being squashed — and a small gap costs far more than the same fraction of area suggests, because heat takes the easy route. Insulation compressed into a space is also working below its rating. Fitting carefully is worth more than buying a higher grade and stuffing it in.
For a loft, the first layer goes between the joists and the second across them at right angles. That second layer is what covers the joists themselves, which are otherwise a continuous line of timber bridging the insulation from ceiling to loft. Skipping it is the most common reason a loft that looks fully insulated still loses heat in stripes.
Keep the eaves clear — a cold loft needs air moving through it, and insulation pushed tight into the eaves blocks the ventilation path and leaves the roof timbers damp. Do not insulate under a cold water tank: insulate around and over it and leave the loft below uninsulated, so warmth from the house stops it freezing. Recessed downlights and flues need their specified clearances, and insulation laid over a non-fire-rated downlight is a fire risk. Look at the joists, wiring and any damp stains before you cover them, because once the insulation is down you cannot see any of it.
In two layers, crossed: the first between the joists, the second across them at right angles. The crossed layer is what covers the joists themselves, which otherwise bridge the insulation and lose heat in stripes.
No. Insulate around and over the tank and leave the loft below it uninsulated, so warmth rising from the house stops it freezing. Insulating underneath is how tanks freeze.
Yes. A cold loft needs air moving through it, and insulation pushed tight into the eaves blocks that path and leaves the roof timbers damp. Eaves vents or baffles hold the gap open.
Yes — compressed insulation works below its rating, and a small gap loses far more heat than its share of the area, because heat takes the easy route. Fitting carefully matters more than buying a higher grade.