Template:All systems - ROOF DECKS

1 General

The roof deck must comply with several guiding principles, to be suitable for a RoofStar Guarantee:

• For low slope (membrane roof or waterproofing systems) it should provide positive slope to drain [required for a Five (5) or Ten (10) year RoofStar Guarantee for new construction and for organic felt membrane systems when re-roofing]. Positive slope to drain is attained when no standing water remains on the deck within a reasonable amount of time after rainfall stops during days with conditions that permit evaporation. Where required, crickets and saddles should be provided to assist drainage. Slope can be provided by sloping the deck, or using tapered insulation boards or insulating fill (insulating fill is rarely used in B.C.). Tapered slope insulation products can only be used to provide slope if any differences from level in the roof deck are less than the percentage of slope provided by the insulation. A minimum slope of 1:50 (1/4" in 12") is strongly recommended. The exception is often drain wells that are designed to collect water and provide a flat surface for the installation of roof drains. Therefore, standing water may remain in drain wells for a longer period of time after a rainfall stops.
• It should be dimensionally stable and capable of accommodating roof system component movement.

• Deck deflections should be limited to 1/240 of the total span, but must conform to the Building Code. For plywood decks, RGC limits the allowable deck deflection to 1/360 of the total span to prevent differential edge movement. Concentrated, non-uniform construction loads should be considered during design. Drains should be located at points of maximum deflection whenever possible, not over columns or bearing walls. Building settlement can often cause slopes to change and low spots to appear on the roof surface.

Prior to the commencement of roofing, any curbs, cants and blocking that are to be installed by others, should be in place.

2 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.

3 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.

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.

4 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. Detailed as-built drawings should be made to prevent conduit damage and safety risks to roofers, should the roof require replacement at a future date.