Loft insulation, laid to depth and without blocking the eaves.

Two layers, crossed

The first layer goes between the joists, usually 100 mm. The second goes across them at right angles, usually 170 mm, which is what covers the joists themselves and stops them acting as a line of cold bridges straight through the insulation.

That second layer is the one that gets skipped. A loft with 100 mm sitting neatly between the joists is roughly half-insulated, and it is a common find on surveys.

Ventilation and the things in the loft

Insulation pushed hard into the eaves blocks the airflow the roof void needs, and a cold unventilated loft gets condensation. We keep a clear gap at the eaves and fit ventilation trays where the pitch is shallow.

Pipework and any cold-water tank sit above the insulation, in cold air, so both get lagged. The hatch gets insulated and draught-sealed — an uninsulated hatch is a hole in the middle of an otherwise good job. Downlights and flues get kept clear to the required distance.

If you store things up there

Laying boards straight onto the joists squashes the insulation flat and undoes most of the benefit. If you need storage, we raise the deck on loft legs so the full depth stays loose beneath it, and board only the area you actually use.