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Under One Roof

Canadian Roofing Reference Manual

3.2.3 Keeping Roof Watertight

During the entire re-roofing operation, it is very important that water is permitted to drain from any area that is being re-roofed. Blocked drains or scuppers, or no drains available on a roof area will allow water to be trapped.

All rainwater scuppers and drains must be protected and all protection must be removed at the end of each day. Plugging drainage devices (hoppers, drains) with paper etc. is not considered good roofing practice. A small, lightweight sandbag is much easier and far more practical. It must be remembered that loose debris left on the roof maybe washed down to the rainwater hopper should heavy rains occur, so at the end of each working day debris guards must be available and in place.


When tie-ins are required, much care and consideration must be given. At the end of each work day, the area to be tied-in for the following day must be properly sealed to the finished membrane to ensure the roofing assembly that has been installed (insulation, cover board etc.) is protected should precipitation occur. Roofing assemblies that remain open to weather will absorb moisture that is sometimes only surface-dried and may cause buckling and blistering at the tie-in location in the future years that may contribute to a roofing failure.


No roofing materials should be removed unless it is possible to maintain the premises beneath the roof in a watertight condition. Daily weather forecasts should be taken into consideration.