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How to install synthetic rubber flashings
Rules for installation
Synthetic rubber flashings are a type of flexible rubber roof flashing designed to create a watertight seal around roof penetrations like pipes, flues, vents and conduits.
They are made from materials such as Ethylene Propylene Diene Monomer (EPDM) rubber or silicone and are often equipped with a flexible aluminium band for added support and flexibility. They are generally known for their durability and ability to withstand harsh weather conditions.
It is often assumed that if the flashings are made watertight, that there are no specific installation requirements, but this is not the case.
What are the requirements?
Both manufactures of synthetic rubber flashings and HB 39 - Installation code for metal roof and wall cladding note specific installation requirements. HB 39 requires that synthetic rubber flashings are installed to manufacturers specifications and do not block the flow path of water on the roof.
An example of where this may occur is shown in Figure 1. The synthetic rubber flashing is installed on a metal tray deck roof over more than two ribs. This creates potential for a ‘dam’ where the flow of water is interrupted. Careful planning or use in combination with other flashing can avoid the issue.
Figure 1
Another consideration is water ponding at the base of the flashing. This can be avoided through use of a ‘dry pan’ flashing which are suitable for both trapezoidal profiled roofing and corrugated roofing (see Figure 2).
It is also recommended that if the installation of the flashing interferes with the pan (bottom of the corrugation) of the roof sheet, that a pan flashing be installed to prevent any potential water ingress and ensure a weather-tight seal.
Figure 2
Installing synthetic rubber flashings on a diagonal axis to the profile of the roof sheet provides more efficient water shedding.
It is important to note that penetrations through the rib of the roof sheet require silicone to seal the penetration to the roof sheet. This will eliminate the risk of any condensation between the dry pan flashing and the penetration running down inside the roof cavity.
When installing a dry pan flashing it is recommended the pan flashing be wide enough to allow 1x full rib to be covered either side of any penetration. This eliminates any chance of water during heavy rain flowing back under the tray entering the penetration.
To find out more, contact HIA's Building Services team.
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