Timber frame insulation

[Colin Green]

I'm about to build a timber framed play room in the garden. I've noticed that insulation board is always 5mm thicker than studwork timber (100/125/150mm vs 95/120/145mm). What is the usual practice to get around this? I can't see builders shaving down the insulation or building up the timber. As I'm planning a warm roof style build up, I dont want an air gap either. What should I do?

 

[^woody^]

Just board over it

 

[John D v2.0]

Warm roof is insulation on top of the rafters so the relative thicknesses wouldn't be relevant

 

[Colin Green]

Warm roof is insulation on top of the rafters so the relative thicknesses wouldn't be relevant

Should have known not to try to use my own short hand. What I mean is that I don't want to ventilate above the insulation, so the cavity fillled with insulation must be full. The insulation will be between the rafters and between the studs. The vapour barrier will be between the inner surface and the timbers/insulation. I know this is not a conventional warm roof structure but to keep to the 2.5m height limit, that's what I have to do.

Is a 5mm gap between the vapour barrier and the timber asking for trouble? Would I be better off with a 5mm gap between the joist and the outer deck?

 

[John D v2.0]

fair enough, that's an unventilated cold roof then https://www.jjroofingsupplies.co.uk/blog/warm-roof-vs-cold-roof-whats-the-difference/
and I would keep any gaps towards the warm side of the insulation, having an unheated unventilated void isn't a great idea.