The Government recommended minimum depth is now 270 mm, which is usually made up of two layers of 100mm and 170mm. In the area to be boarded the depth of the joists to which the boards are to be fixed limits the depth of insulation. If you would like to have insulation installed the following prices apply.
100mm layer £6.00 / sq metre
170mm layer £7.50 / sq metre
This excludes the removal of any existing insulation, which would need to be priced on an individual basis.