It is important to remember that local building surveyors will almost always check the roof tile or slate is suitable for your pitch. Laying a product below its minimum pitch can prove to be a costly mistake, so it is always important to check what is being used and whether it is suitable.
If you do decide to install roof tiles below recommended minimum pitch for aesthetic reasons, then the tiles should not be relied upon for performance. However, there may be proprietary sub-roof systems on the market by others to install beneath the tiles to provide this necessary function. In these instances checking exposure is very important because the higher the rainfall, then the riskier this approach is. Our advice follows the BS 5534 recommendation that ‘a roof designed below the recommended roof pitch should have a functional weatherproof sub-roof system to remove any rainwater ingress safely to the rain gutter.’