Cold Flat Roof Insulation Between Joists

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Cold flat roof insulation between joists.

The insulation is below the deck but above the plasterboard. It allows insulation to be added without having to replace the waterproofing on. The majority of domestic cold flat roofs use insulation between and under the joists. 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.

This is used for refurbishment e g. Refurbishing an existing timber joisted flat roof which has no insulation. A cold flat roof is one where the insulation is between or between and below the roof joists. This method of insulation can also be used to upgrade the thermal performance of an existing roof without affecting the waterproofing system.

The rule of thumb for foil faced boards like thermapitch tp10 or kooltherm k7 in this scenario is that you can have no more insulation under the joists than you have between the joists. Insulation is placed in between the joists underneath the roof surface above. 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. 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.

It is preferred to have the bulk of the insulation between the. How to insulate a flat roof. 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. In the warm flat roof construction there is insulation packed into every possible space where air can flow.

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. Poly to the underside of joists. 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. 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.

No ventilation is required for these types of roofs. 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.