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Under One Roof

Canadian Roofing Reference Manual

7.1.2 Deck and Substrate Preparation

Prior to installing any roof system, a deck should be visually inspected to verify that it is smooth, clean, dry and free from any irregularities.

Any bituminous substances must be removed prior to the installation of a thermoplastic membrane as most of these membranes are incompatible with bitumen and will degrade rapidly when in contact with bituminous substances or their residues. If the bitumen cannot be removed, a separation layer consisting of a thin layer of insulation or a protection mat must be installed or an asphalt compatible membrane must be used.

Different types of decks or substrate have different preparation requirement to ensure proper installation of membrane. Concrete

Concrete decks must be fully dry and have a smooth surface. This may require grinding of the concrete surface to remove fins and protrusions prior to installation of the membrane, or the installation of a protection board or mat over rough surfaces.

Precast concrete must be level to provide a smooth surface. In fully adhered systems, roof joints should be grouted to prevent seepage of adhesive. Wood

Wood sheathing decks must be exterior grade, securely fastened, air or kiln-dried lumber. Do not apply a fully adhered thermoplastic membrane directly to pressure treated wood as the adhesives are not compatible with the preservatives used in treated wood. Dimensional lumber decks must be covered with exterior grade plywood, good one side, or a suitable layer of insulation. Steel

All decks must be clean and dry prior to the installation of any roofing material. Thermoplastic membranes cannot be installed directly over steel decks; a levelling layer of a suitable insulation, plywood, or gypsum board must be installed over the deck prior to installing the thermoplastic membrane. Insulation

The purpose of insulation is to provide a proper substrate to install the roof membrane and to provide thermal resistance. It is important that only insulations compatible and approved by the membrane manufacturer be used with thermoplastic membrane assemblies. In loose-laid ballasted and mechanically fastened systems, many different types of insulation can be used. However, some insulation such as polystyrene or fibreglass foam require a protective slip sheet over them. Note that expanded or extruded polystyrene insulations cannot be used in direct contact with PVC roof membranes. In addition, insulation with bituminous facers may require a separation layer. Only specific types of insulations can be used in fully adhered systems. These insulations must be solvent resistant and have suitable facers. Always ensure that the membrane manufacturer’s approved insulation is used for the particular system type.