In flat roof build ups thermal insulation can be placed above or below the roof deck (structural deck, plywood metal etc) or even above or below the waterproof layer.
With cold deck construction the insulation is placed below the deck, this build up type requires ventilation below the deck to stop vapor condensing on the underside. Venting the underside of the structural deck can be impractical and a waste of space. This "Cold Deck" construction is advised against by Modern Roofing and is recommended to be avoided industry wide.
With warm roof construction the insulation is placed above the structural deck, whether above or below the waterproof layer does not matter. In this "Warm Roof" construction there is no need for additional ventilation
In roof construction the risk of condensation can be greatly reduced by the use of a quality vapour control layer (VCL). This VCL should be lapped and/or sealed at joins and openings to reduce the risk of vapour transfer into the colder roof areas.
Modern Roofing only use the following Sarnafil vapour control layers as this VCL is universally accepted as the best on the market.
Sarnavap 1000E
Sarnavap 1000E is a 0.20mm thick polyethylene based vapour control layer, with a moisture vapour transmission rate of 800 MNs/g. Manufactured from special types of polyethylene, blended to produce a vapour control layer that is flexible when cold, resistant to chemicals and ageing and rot proof. Sarnavap 1000E is suitable for use in most mechanically fastened systems.
Sarnavap 500E
Sarnavap 500E is a 0.15mm thick polyethylene based vapour control layer, with a moisture vapour transmission rate of 450 MNs/g. Sarnavap 500E is suitable for use in most mechanically fastened systems.
Sarnavap 2000E
Sarnavap 2000E is a 0.225mm thick high performance polyethylene based vapour control layer, with a moisture vapour transmission rate of 1500 MNs/g. Suitable for use in high internal humidity environments (when used in a loose laid system only), SarnaVert green roofing systems, loose laid ballasted warm roofing systems and all mechanically fastened systems.
Sarnavap 5000E SA
Sarnavap 5000E SA is a 0.60mm thick multi-layer self-adhesive vapour control layer, made of polymer modified bitumen with a glass-fibre mat reinforcement and an aluminium foil top layer. The laminated aluminium foil ensures a high moisture vapour resistance of >9000 MNs/g and a moisture vapour transmission rate of <0.04 g/m²/24hr, including green roofs and high humidity buildings, e.g swimming pools.