Template:Deck Overlay - EPDM, TPO

1 Concrete

• Concrete decks, curbs and equipment pads must be clean, dry, and smooth prior to commencement of roofing.
• Poured concrete or lightweight concrete decks are not to be roofed for a minimum of 28 days after pouring unless expressly instructed in writing by the Project Structural Engineer.
• All concrete decks to receive adhered asphaltic roofing shall be primed.
• A vented base sheet is required under all asphalt-adhered (adhesive, mopped or torched) roofing membranes that are adhered directly to concrete decks unless insulation is installed directly above or over the membrane.

Pre-cast panels, post-stressed beams, or “T” and cavity decks shall must have a separation layer such as fibre board, gypsum board, plywood, proprietary overlay board etc. applied over the deck prior to the application of the roof membrane. Where a difference exists in the levels of adjacent surfaces, the general contractor or others shall install grouting. This grouting shall be feathered on the lower surface a minimum distance of twelve times the amount of the vertical differential.

2 Steel

When a membrane is specified for application directly over a steel deck, the RoofStar Guarantee Standards require a steel deck overlay of gypsum with fibreglass facers and a silicone treated gypsum core (see min. standards below), or plywood having a minimum thickness of 12.7 mm (1/2"). Where an underlay is used as a thermal barrier, it must conform to the applicable code and insurance requirements for the roof assembly.

.1 Gypsum Board on Steel Decks

Gypsum boards installed over steel decks as substrates for primary roof membranes must be a minimum thickness of 12.7 mm (1/2") RGC accepted overlay boards. All edges of the gypsum board are to be fully or intermittently supported by the deck and end joints to be staggered (offset) 300 mm (12") from adjacent board rows. A minus offset tolerance of 50 mm (2") maximum will be permitted to compensate for variance in the manufacturers’ tolerance of differing board widths and lengths.

.2 Gypsum Board Attachment on Steel Decks

When gypsum board is required on steel decks as a substrate overlay, the gypsum board can be fully mechanically fastened to the deck or adhered with proprietary polyurethane foam adhesives acceptable to the primary roof system manufacturer. Attachment must meet or exceed the CSA A123.21-14 requirements for the building dimensions and geographical location.

RGC maximum deck flute width and minimum fastener requirements for gypsum board in a deck overlay application are as follows:

Gypsum Board Thickness	Deck Flute Width	Gypsum Board Size	Screws & Metal or Plastic Stress Plates	Bugle Head Drywall Screws
12.7mm (½")	up to 125mm (5")	1200 mm x 2400 mm (4' x 8’)	12	32
15.9mm (5/8")	up to 200mm (8")	1200 mm x 2400 mm (4’ x 8’)	12	32

When gypsum board is used under mechanically fastened insulation, the gypsum board must be fastened independently from the insulation. The minimum number of fasteners(screws or screws and plate) is four (4) per sheet. Adhesive systems must meet or exceed the CSA A123.21-14 requirements for the building dimensions and geographical location.

3 Wood

An RGC accepted rigid insulation / overlay board mechanically attached or semi-adhered membrane (spot or strips) is required over non-veneer panels before fully adhered roofing membrane is applied.