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The synthetic slate chosen for this small roof replacement is very popular.
It’s lightweight, cheaper to buy than a natural slate and quite aesthetically pleasing.
The fixing instructions have changed for this slate relatively recently.
Being such a smooth and close fitting slate, a standard breather membrane can encourage condensation.
To negate this problem, the manufacturer suggests installing a counter battern to form a 50mm air gap.
This however is not always a viable option. In this scenario, counter battening would have raised the profile of the roof too high and caused an issue in the top right hand corner against the mansard above.
A ‘non breathable’ membrane was therefore installed and the cavity was vented using slate vents.