We are in the middle of a large redevelopment - the property has a mansard roof (I didn't know what this was until recently). Long story short, the first floor rooms are kind of in the roof (see example pictures).
The builders have put 100mm Kingspan between the rafters, and 25mm PIR on top of that - they intend to fix the plasterboard directly onto the 25mm PIR (as an alternative to fitting insulated plasterboard). The PIR will be taped at seams.
They question is - is a vapour control layer advisable, given that the mansard is technically a loft conversion. If a VCL is advisable, should it be between 100mm Kingspan between the rafters and the 25mm PIR to the underside - or should it be over the combined 125mm (so the plasterboard goes directly onto the PIR? The builders say they don't usually put VCL in.
Kind of related - we have installed 2 wood velux windows in these rooms - and I've noticed that the velux vapour barrier is missing (it seems like an optional piece of kit from velux) - is it necessary?
The builders have put 100mm Kingspan between the rafters, and 25mm PIR on top of that - they intend to fix the plasterboard directly onto the 25mm PIR (as an alternative to fitting insulated plasterboard). The PIR will be taped at seams.
They question is - is a vapour control layer advisable, given that the mansard is technically a loft conversion. If a VCL is advisable, should it be between 100mm Kingspan between the rafters and the 25mm PIR to the underside - or should it be over the combined 125mm (so the plasterboard goes directly onto the PIR? The builders say they don't usually put VCL in.
Kind of related - we have installed 2 wood velux windows in these rooms - and I've noticed that the velux vapour barrier is missing (it seems like an optional piece of kit from velux) - is it necessary?
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