Garden room roof insulation

[Jonny]

Hi everyone,

I'm currently building a garden room, it will be site office, come long term office/further accom over time. Built to be non permanent, it is on piers with a 8x2 base, 4x2 walls and 6x2 roof with 10 deg pitch. The room is around 20sqm. 

 

I thought I had cracked this insulation malarkey, but now I'm not sure. I've also already bought the materials without double-checking. For the walls, I was planning 100mm 035 mineral wool with 50mm pir internally. This would have a breather membrane externally and Proclima Intello Plus internally. 

 

For the roof, I was aiming for a warm roof with 100m PIR on the deck with 100mm mineral wool between rafters. I'm not sure, though, after seeing the attached UBAKUS calculation, which suggests a very poor drying time. Have I got the membranes in the wrong places or something else? 

 

I've attached a photo of the current state of the building - still some structural work required on it and also the Ubakus PDF printout. 

u-wert-berechnung (5).pdf

[JohnMo]

20 minutes ago, Jonny said:

For the roof, I was aiming for a warm roof with 100m PIR on the deck with 100mm mineral wool between rafters

Classic bad design hybrid roof - that is the cause of your issues. Either do the insulation above or below.  If doing both a smaller amount below than above.

[Jonny]

Thanks, did have an inkling that may be the case. I’ll try again on the calculator tomorrow with the 100mm PIR only and report back. It’s not going to have a high heating demand. 

[JohnMo]

Or you could do mineral wool between and PIR below

[saveasteading]

Excuse my ignorance. What is this 'drying time'? 

Use dry wood, keep the rain out....

If if isn't dry, then don't cling wrap it until it is?