Cold Flat Roof Insulation Between Joists

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.

Cold flat roof insulation between joists.

Great videos thanks for sharing. 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. Both these variants require different approaches to insulation which will be covered in this guide. 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.

No ventilation is required for these types of roofs. As there are two types of flat roofs available that require different types of insulation the methods used. 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. Insulation is placed in between the joists underneath the roof surface above.

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. Creating a void between the old ceiling and new is better but ideally you need to eventually consider insulating the top of the concrete roof with solid insulation and a better. Poly to the underside of 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.

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. Typically a gap will have to be left for ventilation because this is a cold area. This method of insulation can also be used to upgrade the thermal performance of an existing roof without affecting the waterproofing system. 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.

Cold deck or cold roof is where the insulation is below the roof deck and the associated joists.