Warm Deck Flat Roof Systems
Warm Deck Roof Designs for EPDM
The warm deck roof design is the modern method for flat roof construction and is preferred wherever this option is possible.
So called because the insulating layer is located above the roof rafters and between the structural supports, a warm deck roof results in a temperature for the roof and loft area that is consistent with the rest of the property.
In a cold deck roof construction, the insulation is laid between the ceiling joists and over the ceiling. This results in the roof and loft area being colder than the rest of the property.
Previously, the cold deck method of flat roof construction was favoured. However, with changes in how people live and how properties are utilised, this has now changed.
Constructing a Flat Roof Using EPDM
Warm deck flat roofs can be constructed on most modern construction material types such as concrete, timber and timber based sheets.
To use EPDM for a warm deck flat roof construction, solid (closed cell) roof insulation such as Kingspan or Celotex should be placed on top of the roof deck, rather than in between the rafters.
A vapour barrier will then need to be installed to reduce condensation in the roof structure. The insulation and vapour barrier can be mechanically fixed using fasteners and washers or a self-adhesive vapour barrier such as Alutrix can be installed with insulation bonded on top, using PU Adhesive Battens. This removes the need for mechanical fasteners that can cause cold bridging.
When installing EPDM, existing membranes such as BUR or felt can be left in-situ to be used as the vapour barrier, so long as the roof deck is in good order and does not need to be replaced due to water damage. In this scenario, the insulation can be glued onto the existing roof covering using a PU adhesive.
To construct a mechanically fixed warm deck using EPDM, you will require:
- Roof deck - minimum 18mm ply or OSB3 (Oriented Strand Board) deck
- New vapour barrier (or leave the existing felt membrane in-situ if this has not suffered water damage)
- Kingspan TR26 foil backed insulation, or similar
- 9mm / 11mm ply or OSB3 board
To do this, you will need to:
- Overboard the insulation with a 9mm / 11mm ply or OSB3 board
- Screw the 9mm board and insulation down into the existing roof joists
- Install EPDM rubber roof as per installation instructions
To construct a self-adhesive vapour barrier for a warm deck roof, you will require:
- Roof Deck, minimum 18mm ply or OSB3
- Insta-Stik PU Adhesive Glue
- Kingspan TR27 tissue faced insulation or similar
N.B. The Self Adhesive Vapour barrier offers significant advantages over screw fixing as it enables the roof to be made watertight prior to the EPDM rubber membrane being installed
Please consult Part "L" building regulations as the information printed above may have been superseded. We have attached a link here from London Flat Roofing explaining a little more about your obligations as a roofer and homeowner under Part L Building Regulations in relation to flat roofing: