Deck and Wall Overlays
Deck and Wall Overlays
1 General
NOTE: Refer to subsection 3 (SUBSTRATES - DECK OVERLAY BOARD and WALL SHEATHING) of the RoofStar Guarantee Standards for either Low Slope Roof Systems or for Architectural Sheet Metal Roof Systems.
A roof system underlay is installed under the roof system and over the roof deck assembly. Underlays are most commonly placed over steel decks to provide a level surface for the membrane, or as a thermal barrier between the roof deck and combustible insulations.
RGC requires either minimum 12.7 mm (1/2") gypsum with fibreglass facers and a silicone treated gypsum core (See Section 2.1, A2.5) or minimum 12.7 mm (1/2") plywood as an underlay for membranes installed directly over steel decks. Where an underlay is used as a thermal barrier, it must conform to the applicable code and insurance requirements for the roof assembly.
2 Underlays for Metal Roofing
Acceptable membrane underlays for metal roofing are listed in Section 8.2 and in Section 2.2 (accepted Materials list) of this manual.