Cold Flat Roof Insulation Between Joists

The major difference between the warm flat roof and the cold flat roof has to do with the air flow between the roofing timbers known as joists that help to hold up the roof.

Cold flat roof insulation between joists.

Cold deck roof a cold deck roof is where the insulation is placed between the joists rafters or in between the ceiling joists in the case of a pitch roof. As there are two types of flat roofs available that require different types of insulation the methods used. Typically a gap will have to be left for ventilation because this is a cold area. Saint gobain insulation uk manufacture and supply glass mineral wool slabs and rolls along with rigid polyisocyanurate pir boards that can be considered suitable for a wide range of applications across flat roofs whether you re looking to insulate at joist level or above the roof deck in your flat roof construction.

No ventilation is required for these types of roofs. Great videos thanks for sharing. Where insulation depth is restricted by the flat roof construction it may be necessary to install the roof insulation between and below the joists to create a cold deck structure. Insulation is placed in between the joists underneath the roof surface above.

A warm deck roof is where the insulation is placed on top of the rafters joists and the roof covering is then placed over the insulation. Cold deck or cold roof is where the insulation is below the roof deck and the associated joists. This quetion is to do with warm roofs and cold roofs presumably the 50mm of insulation on the underside of joists would act as the vapour barrier if taped sealed correctly or if insulation between joists a vapour barrier i e. Alternatively battens can be secured to the underside of the joists and gmw fitted between these in much the same way as between the main roof joists.

Flat concrete roofs are generally not ventilated since the ceiling internally is generally a plaster and skim coat directly to the underside of the cold concrete. In the warm flat roof construction there is insulation packed into every possible space where air can flow. This method of insulation can also be used to upgrade the thermal performance of an existing roof without affecting the waterproofing system. The underside of the rafters in this case will need to be finished with a suitable vapour control layer vcl and plasterboard to provide a suitable internal finish to the roof.

Both these variants require different approaches to insulation which will be covered in this guide.