Template:All systems - ROOF DECKS

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.

Steel

.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.

Wood

All wood decks shall be properly fastened to B.C.Building Code requirements. With the exception of standard insulated roof systems, all knots or cracks shall be covered with metal prior to acceptance of deck surface.This work is to be done by others.

Non-veneer (O.S.B. or wafer board) panels are acceptable sheathing for decks with low-slope roofing applications, provided the roofing membrane is not fully adhered directly to the panels.

The minimum plywood or non-veneer (O.S.B or wafer board) deck thickness for low-slope roofing (i.e., membrane roofing) shall be a minimum 12.7 mm (1/2")and as indicated in the applicable Building Code.

An RGC approved separation sheet, minimum#40 asphalt coated fibre glass base sheet conforming to CAN/ CSA A123.16 - M88 (R1996), Type II or manufacturer’s accepted base sheet of equal or greater weight and reinforcement, or 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.

Direct torch (open flame) membrane applications to wood decks and wood surfaces is NOT permitted. For further development of this policy, refer to SBS Application & Safety: Best Practices.

Differential edge movements or deflection in excess of1/360 of the span in plywood or non-veneer decks in low slope roofing must be prevented by:

• solid blocking under non-supported edges, and /or
• use of tongue-and-groove plywood with non-grooved edges supported by joists or solid blocking, and / or
• when rigid insulation is over the deck, properly sized and installed H-clips must be used on the unsupported edges.

Fully adhering modified bituminous membranes directly to wood decks is not permitted.

SPECIAL CIRCUMSTANCES (Electrical Conduit)

Conduit, EMT, cable and/or piping applied on the top of roof deck surfaces shall not be acceptable on new construction projects. If conduit is present on decks in re-roofing projects, the deck must be made smooth and even to the satisfaction of the accepted roof inspection firm. The upper layer of insulation must cover the conduit, EMT, cable and/or piping.