Garden room electrics

It is fine but do use an appropriate back box, either a dry lining type or metallic

https://www.tlc-direct.co.uk/Main_Index/Boxes_and_Enclosures_Index/Boxes_Dry_Lining/index.html

Also I assume there is a vapur membrane somewhere - reseal it at any breaks.

Mike.

Thanks Mike.

The building will be of structural insulated panels with a breathable membrane on the outside under the cladding. I wasn't aware I'd need one on the inside.

Mike

I'm probably out of date now but when I was doing such things it was a breathable membrane on the outside and an impermeable membrane on the inside to stop warm moisture laden air from the living space condensing inside the timber frame.

Yes I can see that a vapour barrier might be necessary. More research needed  ...

Thanks.

Mike

Bear in mind that if the cables are embedded on or in the insulation, then their current-carrying capacity gets reduced (sometimes quite significantly).

Yes I understand that, but the insulation is sandwiched between the OSB while the cables are on the surface.

From what I've just read, providing the joints between the SIPs are properly sealed a vapour control layer isn't needed.

Mike

Have you read anywhere that a membrane could be detrimental? This is your own place isn't it? It's cheap. It's easy to install. Why wouldn't you?

Yes I have, if moisture finds its way between the vapur barrier and the OSB.

I'm going to ask the manufacturer of the SIP kit for their advice.

Mike

Nice fresh circulating air is timber's friend. It reduces the chances of rot and fungus growth. Why not just surface wire internally?

Z.

Good point. It would certainly be cheaper and a lot quicker. Not so neat but I can probably live with that.

I've spoken to the SIP manufacturer and they say that the SIPs act as a vapour control layer and providing the room is used as an office and not as a gym or sauna no additional vapour barrier is needed.

Mike