Loft Insulation Between Roof Joists

Joists are the horizontal beams which make up the floor.

Loft insulation between roof joists.

This involves insulating between and over the wooden joists immediately above the ceiling of your top floor. 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. Lay mineral wool between the joists and then fit rigid insulation boards across the joists with floorboards on top. 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.

A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. 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. Typically the gap between the joists is either 380mm or 570mm so you will need a width of insulation similar to this so it can fit snugly between the joists. Between and under joists.

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. You could even buy insulation and floor boards that are already bonded together which makes the job much faster and easier. Rolls of mineral wool can be used if the joists in your loft are regular. 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.