Vapour-permeable membrane: what is it?
Vapour-permeable membrane allows moisture to escape from the building structure. This prevents condensation and thus mould in your structure and insulation materials. This membrane is often wind and rainproof. The structure must always be vapour-permeable towards the exterior.
Vapour-permeable membrane: the metaphor of a wool jumper and a breathable raincoat
You've probably experienced it. You're walking outside in winter in your wool jumper. Fine for a short while. But the moment you encounter strong headwind, you suddenly don't feel so warm anymore. This is because a wool jumper keeps you warm by trapping still air between the wool fibres. In a strong wind, this air is simply blown out. You can prevent this with a windbreaker or raincoat. But with a non-breathable jacket, another problem immediately arises. The moment you start sweating, it can get quite damp inside. This can be compared to a vapour-proof membrane that prevents moisture from escaping. Ecological building is vapour-permeable building, where moisture can escape from the home and the structure to the outside. In ecological building, the membrane that provides wind and rainproofing is therefore vapour-permeable. And thus comparable to a breathable raincoat.
Vapour-permeable membrane from the brand: Pro Clima, type: Solitex Mento 1000
Wind and rainproofing with membranes or sheet material
In existing homes, you may encounter building sections that are no longer windproof. Over the years, gaps may have appeared in, for example, your sarking felt, around window frames and/or between and within floors and walls. It is therefore advisable to check the wind and rainproofing of the building section to be insulated beforehand.
A building section can be made wind and rainproof with special membranes or with sheet material, the seams of which are taped. Ensure that this layer is not accidentally perforated by something sharp in the existing roof, such as a forgotten nail, otherwise air and water leaks may occur. The choice between a membrane or sheet material depends on the price, the amount of processing required with corners and exceptions, etc.
