A ventilation gap, usually 50mm, should be provided between the top of the insulation and underside of the roof covering to allow the air to flow across.
Dylid gadael bwlch awyru, sef 50mm fel rheol, rhwng wyneb uchaf y deunydd inswleiddio ac wyneb isaf gorchudd y to er mwyn caniatáu i'r aer lifo drwodd.