Options to reduce insulation thinkness in loft conversion

[strath44]

We are soon starting a loft conversion and the architect has spec'd 150mm of rigid insulation (kingspan etc) between joists and 37.5mm Kingspan k18 or similar (plasterboard + rigid insulation) as the finishing over the top of this.

Space is a bit tight are there any options other than the kingspan k18 that will offer the same u value but not as thick?

[strath44]

It's been a real war of attrition this whole area.

The original spec was 100mm in between the rafters with 50mm air gap at sarking, however as the roof joists terminate in the wall head there is no eaves gap or air flow. The BC first requirement with this was to fit a roof vent to every joist space - this would have made the roof look ridiculous with 20 vents in a 9m run.

Anyway we found a new solution and this is the last issue I want to address so yes I am carefully considering it as I do worry about interstitial condensation!

[strath44]

Indeed, that was actually the route we went in the end!

[strath44]

Wolfracesonic - he did and I was told there wasn't any options but I'm the sort of person that likes to make sure!

[strath44]

The things is that our house was built in 1830 there are so many variables that have to be managed to achieve the said u values its important to keep all factors in consideration!