Currently working through an extension and was talking with the builder and carpenter about subfloor insulation options.
Subfloor consists of 140mm joists with 90mm insulation batts planned to go between. Is there any advantage to increasing the insulation thickness without doing anything else? Other options i've thought about:
- Standard 90mm batts on straps (Earthwool® R2.5 FloorShield Underfloor Insulation)
- Standard 90mm batts with the addition of a vapour permeable membrane beneath (Earthwool® R2.5 FloorShield Underfloor Insulation and VapourFlex-VPM | Reflex Insulation or similar?)
- 140mm thick with a vapour permeable membrane (Polymax | Underfloor Insulation Experts or something else with higher R-value?)
- Spray foam (Underfloor Insulation Perth | Insulation Extract)
I can add the membrane myself after the fact, although the chippy likes the idea of doing it straight up so he can use it to lay on while installing batts first.
Is there a superior option out of all of these?
Thanks