Timber frame dormer window/bathroom

[Dee]

Hi,

Looking for guidance and advice on insulation fir the above bathroom structure.

My late husband and I built the thing about 5 yrs ago and now its upto me to complete it.

Cross section from outside goes thus;

Hardy cladding

Battons

Breather membrane 

25mm marine ply

2 x 4 frame (so undersized l guess!)

Breather membrane 

Rocwool insulation between 2x4

I aim to plasterboard and skim.

 

So...

Should I cross baton 2x4 to strengthen frame?

Should I used the thin foil blanket for additional insulation?

I know I've probably done it all wrong but I have to work with what I have.

Thankyou!

 

[Mr Punter]

Use Celotex instead of Rockwool.  Even better if you top it off with insulated plasterboard.

[Iceverge]

I would use...

 

Hardy cladding

 

Battons

 

Breather membrane 

 

25mm marine ply

 

2 x 4 framing with 100mm Rockwool full fill between ( much easier than PIR to fit) and you still have a very good Uvalue. 

 

100mm of PIR over the framing. Tape all joints for airtightness. 

 

70*20mm battens over the top of the PIR.

 

Plasterboard and skim.

 

U value about 0.145

 

 

[Dee]

Small problem....I don't have the internal space to add another 100mm, +20mm ....its a small bathroom! Any alternatives that take up minimal space?

Thsnkyou so much for your help!

[Iceverge]

Use insulated plasterboard over the 2x4 in that case. As thick as you can get away with.