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Under One Roof

Canadian Roofing Reference Manual

5.2.1 Preparation of Roof Deck

Prior to installation of modified bitumen membranes, the following steps should be completed:

  • Inspection of roof deck
  • Store and load material
  • Prime or insulate deck

Inspection of Roof Deck

Modified bitumen membranes can be applied directly over suitable wood decks or insulation support panels, gypsum and cementitious boards, and concrete decks. The decks must always be clean, smooth and thoroughly dry. A structural engineer should verify that the deck has the capacity to support the weight of the roof system.

  • Wood decks should be a minimum of 15.9 mm (5/8 in) plywood. Verify that it is properly fastened, with no nail heads protruding above sheathing. Irregularities should be noted and reported to the general contractor, owner or owner’s representative.
  • Concrete decks must be completely cured and dried before installation of the membrane begins. Fins and sharp protrusions must be ground smooth prior to the application of the membrane directly to concrete roof decks.
  • Steel decks must be covered with a suitable membrane support panel such as insulation, cementitious panels, or gypsum board. Boards should be fitted to the deck so that the edges rest on the ribs. Secure the membrane support panel to the deck using appropriate adhesives or fasteners applied at a rate or pattern consistent with the design wind uplift resistance requirements and in accordance with the manufacturers’ written requirements.

Ensure that all other trades have completed their installations; curbs, vent pipes, drains, etc. before commencing the roof installation.

Storage of Material

  • Materials should always be kept stored in the original packages, in a dry, well ventilated area. It is recommended that in winter months, materials be stored inside, at a temperature of 10°C (50ºF). Rolls of membrane must be stored on end. Remove from the storage room only the rolls required for immediate use.
  • Determine the roof area where you will start. Leave this area clear and unobstructed when loading the roof deck.
  • Ensure that the weight of materials is evenly distributed to prevent overloading in one area.
  • Cover walls with clean tarps when hoisting material and pumping asphalt to minimize the potential for damage.

As with all roofing materials, care should be taken to ensure that the materials arrive at the job site in a dry and undamaged condition. Precautions must be taken to protect the materials from the elements during storage. By scheduling delivery of materials to the job site just prior to their installation the risk of moisture contamination or damage can be minimized.

Store roll materials on end, placed on pallets raised above the ground or roof deck. Cover all materials not stored indoors with breathable waterproof coverings that have been properly secured. Avoid stockpiling materials in one location and take care not to overload the roof. Handle materials in such a manner so as to prevent damage. Extra care should be taken at lower temperatures as bituminous materials may become less flexible and brittle.

Wet or damp roofing materials should never be used in the construction of a roof assembly. All surfaces to which the roofing will be applied must be dry, firm, smooth, and free of contaminants, dirt or debris. Materials should only be applied in weather suitable for roofing. Acceptable conditions depend not only on ambient temperatures, but on the total combination of nature’s elements, including wind, humidity, cloud cover and solar exposure.

Keep all materials dry and clean.

Priming the Deck

All uninsulated concrete decks must be primed before the membrane is installed. For mopped or torched applications, the primer is typically a petroleum asphalt modified with thermoplastic polymers and volatile solvents. Install primer to the deck and up all parapets and curbs using methods and at the rate(s) recommended by the material manufacturer. Typically, primer application rates are in the order of 0.1 to 0.5 L/m² (0.2 to 1.0 gal/square). Allow primer to dry thoroughly in accordance with manufacturers requirements.

On insulated decks that require a torched on base membrane, ensure that the insulation is suited for torch applied application or cover the insulation with a suitable and approved torch safe cover board properly secured. Many membrane manufacturers can supply insulations that are specifically designed for torching applications. Ensure that all insulation and vapour retarders have been properly secured to the deck with appropriate applications of asphalt, adhesive, and/or mechanical fasteners.