The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
- They are lapped over the roof cladding, creating a dam that holds moisture and dirt.
- They rely on sealant alone for their weathertightness.
- They obstruct the rainwater runoff if they block more than 50% of the pan.
- The E.P.D.M. flashing is flexible and requires structural support for the pipe.
- Their longevity is jeopardised if they are distorted or under stress.
To overcome some of these disadvantages, follow these directions.
- The square base should be turned at 45° to the fall of the roof cladding. This will minimise the obstruction, and dirt and debris are more likely to be washed away. See 8.4B Larger Vent Pipe Flashing and 8.4C Prefered Flashing Design for Larger Vent Pipes
- All surfaces should be cleaned, and sealant should be placed around the flange base of the flashing before it is placed in position.
- All surplus sealant should be removed.
- The penetration hole in the roof cladding should be made through the rib, and the hole should be cut close to a purlin.
- Only one rib of a profile should be cut out, as any further cutting severely depreciates the performance of the cladding. If more than one rib has to be cut, additional structural support is required and an alternative penetration design should be used. See 8.4C Prefered Flashing Design for Larger Vent Pipes.
Because of the disadvantages these flashings offer, they should be avoided in certain situations.
- Never use this on a side lap.
- This type of flashing is unacceptable on asymmetrical trapezoidal profiles if the size of the pipe and flashing restrict or obstruct the passage of water to less than half of the normal draining area.
- This type of flashing is unacceptable on symmetrical trapezoidal and corrugated profiles if the size of the pipe and flashing obstruct the passage of water greater than one rib.
- E.P.D.M. flashings should not be used for single flues, and for high temperatures, 60° - 200° HT silicone flashings should be used.
N.B. This penetration design can be used down to the minimum pitch of the roof cladding.