What is a wachtfolie?
A wachtfolie (mainly used in Flanders, literally “waiting membrane”) is a strip of membrane installed in advance at a point where a connecting element or finish will be added later. The strip “waits” for the next layer, so the building’s airtight layer can run on without interruption. The term used to cover both an internal vapour control layer and an external breathable membrane; today it mainly means an airtight vapour control membrane.
What does it look like?
- Narrow strip bonded or taped to the substrate.
- Often fibre-reinforced, making the membrane tougher and easier to embed in adhesive or plaster.
- Plaster-compatible: many such membranes are designed so plaster bonds well to them.
Where is it used?
Typical locations, for example in timber frame construction or renovation:
- Between an external wall and a cross wall, before the cross wall is built.
- Between wall and roof, where the roof’s vapour control layer must connect to a plastered wall.
- Around window frames, where the airtight connection will later be embedded in plaster.
- At continuous floors or beams that interrupt the airtight layer.
Tips
- Plan the build sequence from the start. The strip must go in before the connecting element; afterwards the spot is often inaccessible.
- Leave enough membrane projecting, so the next layer can overlap or be taped generously.
- Use one system. Membrane, adhesive and tape from the same manufacturer ensure bonding on the substrates used.
- Protect the projecting strip from tears and dirt during construction, and inspect it before it is finished over.
- Test airtightness, ideally with a blower door test, before the linings are closed, so leaks can still be fixed.
Related terms
- Airtight construction
- Airtightness
- Airtight tape
- Vapour control layer
- Timber frame construction
- Blower door test
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