Breathable Roofing Membranes
Roofing membranes, or underlay, are barriers installed underneath the roofing covering to reduce the effect of wind loading. They provide a secondary barrier against wind-driven rain and snow. The most common types of roofing membranes fall into two categories, breathable and non-breathable membranes. They both provide a barrier to protect the property from unexpected water leaks, but they are different.
Breathable options have less vapour resistance so water vapour can escape more freely, potentially without the need for separate ventilation above the roofing insulation.
The obvious advantage with a breathable type of membrane is that the risk of condensation is lowered when compared to its non-breathable counterpart. While breathable underlays might not need more traditional forms of secondary ventilation, it is likely that more ventilation such as eaves or ridge ventilation will still be used.