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Insulation for a garden room / studio/ shed (with photos)


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I have a factory-made 18' x 8' brand new garden room. I’m making it into a fully-fitted office/studio with 2 rooms:
– studio for artists work
– kiln room (a pottery oven that gets hot)


Photos & videos: (plus attached diagram)


Our goal is to have a warm workspace and protect our investment.

Roof: (see picture)
– Sloped
– Shed roofing felt on timber decking
– *unvented* (some air seeping in front and back but I’ll seal it)
– 65mm rafters (not very deep!)

Ceilings – (the plan for)
– Plasterboard connected to the rafters in the kiln room (special fire-retardant board on all ceilings/walls in the kiln room)
– Wood cladding connected to the rafters in the studio room
– Ceilings are low - we don't want to make them much lower

For insulation, my research has found these as the 'best' options:
– Warm Roof solutions – not ideal for us
– Cold Roof + Closed Cell Foam – too expensive

I'd like to find the next-best thing - can you please help? :-)

Q1) Ceiling Insulation
– I've been told not to use rockwool style insulation in an unvented roof. Rockwool themselves say it's a condensation risk and that I *can* used their product, but I must usage a smart-VCL with it.
- Celotex told me not to use their product unvented.
- I've had other suggestions a thin layer of EPS across the rafters, no VCL, and either Rockwool or EPS in the rafter cavities.

Note: Ceiling covering in studio room – We want wood cladding but because it's not air tight, the general recommendation is an airtight layer first like plasterboard. However we don't want to eat into our internal space too much if possible...

What do you think we should do for the ceiling insulation?

Q2) Wall insulation – our current plan is:
Rockwool batts filling the cavity
Tyvek Airguard Smart (like membrain) VCL
interior wood cladding.
Again the wood cladding has an impact -- it is used both as the exterior wall and the interior wall, so we're especially concerned about moisture getting in there.

What do you think we should do for the walls?


I know that whatever the product, doing a great job of air sealing it and installing it properly is the most important.

But we are drowning in conflicting views - Thanks in advance for your help!

shed rafter diagram.png

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Also one more q:


Q3)  The floor joists run long-ways left to right and are boxes in by decorative skirting.  (see photo:  https://www.dropbox.com/s/xvar3aequr3qr32/IMG_5540.JPG?dl=0)


I thought to move the skirting up a bit to create air flow underneath, but obviously that opens it up to rodents.  Is it better sealed?  (could warm moist air get under there any condensate on a cold floor joist?) The floor is not insulated (40mm treated floor joints + treated pine timber floor + DPM + underlay + laminate) 


Thank you so much in advance for your help!! ?

Edited by mj62mj62
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Ok I will start, been avoiding it as didn’t want to sound negative. 

Dont put anymore of those studs in place, and stop with the electrics, you need to get your insulation method sorted first. 

If you go with a sheet type you need to cut it at a set width and then put your additional studs in to match the insulation, if not you will end up cutting all funny sized insulation and end up with all manor of waste. 

With regards the electrics,if you bury them in the insulation layer you need to consider the loads as the insulation can compromise the load carrying capacity. 


Have you thought of having it spray foamed. 

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Hi Russell - Thank you very much, I appreciate your insights -- it's not negative, it's helpful ?


Thank you as well for the warning on the electrical load - I'll ask my electrician.

We did look at closed cell spray foam -- done properly it looks good, done badly then there are some scary horror stories out there (health impact, etc).   They quoted me £1700 which was out my price range.  The American forums view the closed cell spray foam as the best unvented cold-roof solution - but £1700 is a lot.



Currently we're thinking about:


Roof & soffit: (from the outside in)

- Rockwool - it solved two problems: available in the right size and it's fire rated which puts my wife's mind at ease for the kiln room

- AVCL (smart vapour control layer - very few shops carry these...)

- Plasterboard ceiling in both rooms



- 50mm Rockwool slabs (leave a tiny 5mm gap between the insulation and the exterior cladding) 


- Plasterboard (we're still unsure if we'll so this - but it adds air tightness across the studs)

- Wood Cladding


Who knew insulating a shed had no many different options!




Edited by mj62mj62
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