Loft Insulation Between Roof Joists

If the loft is going to be used as living space then the insulation should be placed at rafter level to create a warm roof.

Loft insulation between roof joists.

This involves insulating between and over the wooden joists immediately above the ceiling of your top floor. Between and under joists. Most insulation you buy will be partially perforated allowing you to cut the roll of insulation easily to produce either 2 rolls that are 570mm wide or 3 rolls that our 380mm wide. To increase the thickness of your roof insulation layer you can.

But if you simply fill the spaces between the joists with insulation and then board over the top you won t achieve an adequate depth of loft insulation. A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. Unless the joists are exceptionally deep there is also likely to be a requirement to install insulation to the underside of the joists as the upper 50mm of joist space is usually required to be left clear for ventilation purposes. But if you plan to use your loft for storage only then a conventional cold roof option where the mineral wool insulation rolls are placed in between the ceiling joists above the top floor.

Lay mineral wool between the joists and then fit rigid insulation boards across the joists with floorboards on top. The first layer of wool is placed between the joists and then a second layer is placed at right angles which covers the joists and also makes the insulation up to the correct depth of 270mm. You could even buy insulation and floor boards that are already bonded together which makes the job much faster and easier. Joists are the horizontal beams which make up the floor.