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Under One Roof

Canadian Roofing Reference Manual

4.2.2 Installation

Deck Preparation

The roof deck (or substrate (sub-deck or thermal barrier in the case of a metal deck) should be inspected to ensure it is properly prepared and meets or exceeds instructions required by either the architect, the manufacturer of the product, before proceeding with the application of the roof assembly.

Vapour Retarder

The vapour retarder should always be one continuous unbroken seal, which is typically one or two-ply coated felt kraft paper installed into cold-applied adhesive or a self-adhered vapour retarder.

Before application, the base felts can be cut into manageable lengths 3 m to 4.9 m (10 ft to 16 ft) and stacked on a clean level surface with the guide lines up. During colder weather, the felts should be stored in a warm area (approximately 20°C [68°F]) for at least 24 hours before using. This cutting and stacking allows the felts to relax and lose any curling picked up while being rolled at the factory.

  • Single Ply Base Felt
    • Starting at the lowest spot on the roof or the drain and at right angles to the roof slope, install a single 1 m (39 in) wide roll of cold process felt. The felt should be fully embedded into the specified cold applied adhesive. End laps should be a minimum of 150 mm (6 in) and should also be fully embedded in cold applied adhesive.
    • Apply the second and all subsequent plies 1 m (39 in) wide and side lap a minimum of 150 mm (6 in) embedded in a full application of the specified cold applied adhesive.
    • All felts should be broomed into place as they are being installed. Once installed, they should be rolled in place with a weighted roller (minimum 32 kg (70 lb)). This rolling will ensure positive adhesion between the membranes and produce a smooth even surface with no air pockets, wrinkles, or open seams.
  • Two Ply Base Felt
    • Starting at the low spot on the roof or the drain and at right angle to the roof slope install a 450 mm (18 in) starter strip embedded in 450 mm (18 in) of the specified cold adhesive, end lapped a minimum of 150 mm (6 in). Set a full roll of cold process felt into the specified adhesive completely covering the starter strip and extending onto the roof deck 450 mm (18 in). All end laps should be staggered from the end laps on the starter strips and lapped a minimum of 150 mm (6 in).
    • Apply the third and all subsequent felts lapped 480 mm (19 in) over the previous sheet leaving 430 mm (17 in) exposed, embedded in a full application of specified cold adhesive.
    • Coat the 480 mm (19 in) of roll of felt just applied and 430 mm (17 in) onto the deck with the specified cold adhesive and install the next full roll of felt. Ensure that end laps are staggered and are a minimum of 150 mm (6 in). Continue to install felt and adhesive until the entire roof area has been covered with the vapour retarder felt.
    • Broom and roll all of the felts as outlined in the single ply application. Some manufacturers require the felts to be rolled using a heat seal roller which ensures a good bond between felts as it warms the material as it rolls it.


When specified, thermal insulation can be installed with a compatible cold-process insulation adhesive. Some types of insulation, for example foamed polystyrenes deteriorate when left in contact with cold applied asphalt adhesive.

Apply a coating of the cold adhesive over the surface of the vapour retarder. The rate of coverage will depend on the manufacturer recommendation, but is generally around 0.8 l/m² (2 gal/square). Immediately embed the specified insulation into the adhesive. Ensure that insulation end joints are staggered and that all joints are tight.

Normally a base layer of insulation is installed followed by a second layer or cover board. Ensure that all joints in base layer insulation or cover board are staggered with the insulation joints of the base layer.


With the exception of the type and application of the cold-process adhesive, the procedure for installing a cold-process built-up roof membrane is similar to a hot-applied built-up roof membrane. Cold-process adhesives can be applied by brush, roller or sprayed- on.

  • Install plies of roof membrane in shingle fashion to shed water, starting at the roof’s low point or at the drain. Apply coated felts perpendicular to the overlay boards. As necessary, conform to manufacturer’s recommended method for cutting and relaxing felts and number of plies required.
  • Install 300 mm (12 in) and 600 mm (24 in) starter strips of felt into cold process adhesive applied at the manufacturer’s recommended coverage rate.
  • For three (3) ply applications: Overlap starter strips 660 mm (26 in) with the first ply, then overlap each succeeding ply 625 mm (24.5 in).
  • For four (4) ply applications: Overlap starter strips 740 mm (29 in) with the first ply, then overlap each succeeding ply 700 mm (27.5 in).
  • Embed plies of felt in a full and uniform application of approved adhesive, applied at the specified coverage rate.
  • Lap ply ends minimum of 150 mm (6 in) and stagger end laps minimum 1 metre (3.3 ft) minimum.
  • Ensure a complete and continuous seal and contact between adhesive and felt plies, including ends, edges and laps without wrinkles, fish mouths or blisters. Thoroughly broom each ply application to ensure full adhesion.
  • Extend plies over and terminate beyond cants and cut evenly.
  • Do not step or walk on felts during or immediately after application until adhesive has set.
  • Overlap any previous day’s work a minimum 600 mm (24 in) as required.
  • Terminate all ply layers to the outer edge of the roof perimeter.
  • In cold weather, the felts should be stacked and stored in a warm area (approximately 20°C (68°F)) at least 24 hours before use.


Once the installation of the membrane has been completed, the flashing membrane can be installed using the appropriate and compatible adhesives. It is common practice to protect the roofing membrane from damage with protection board during the installation of the flashing.


After all roofing and flashing membranes have been installed and are thoroughly dry, the roof can be prepared to receive the surfacing. Prior to any surfacing, all roofing equipment and excess materials should be removed and the roof swept to remove any dirt and debris that may have accumulated.

The two common types of surfacing for cold process roofing. The first is to incorporate an aggregate into the cold-applied floodcoat and the second is use a coating that produces a smooth finish when no aggregate is used.

For an aggregate surface, the floodcoat is generally a solvent based adhesive which is applied at the manufacturer’s recommended coverage rate. The coverage rate is generally 2 to 2.5 L/m² (5 to 6 gal/100 square). Immediately spread clean and dry standard roofing gravel at the rate of approximately 20 to 24 kg/m² (400 to 500 lb/square). If a granule-surfaced roof is desired a top ply of granulated modified bitumen may be installed.

For smooth surface roofs, the roof adhesive must cure completely prior to installation the surfacing. It may take approximately 2 to 4 weeks for the adhesive to fully cure, depending on the type of adhesive that was used. Once the roof membrane adhesive has cured, an asphaltic emulsion can be sprayed or brush applied. A typical manufacturer’s recommended coverage rate is generally 1.6 to 2.5 L/m² (4 to 6 gal/square). If desired, a reflective coating can then be applied following the curing of the emulsion, approximately 7 to 14 days. Alternatively, a high build reflective coating can be used which avoids the need for an asphaltic emulsion coating.