Garden room from Sips

Help Support

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


New member
18 Jul 2022
Reaction score
Milton Keynes, UK
Good afternoon all,

First of all it looks like this forum has a wealth of information and very knowledgeable people, I will be honest I have tried looking for my specific answer but did not find them yet (got stuck reading a full thread where Mike and others were trying to tell a person regarding membranes, moisture etc) but unfortunately did not find info regards to Sips construction and as we are starting the build this Saturday time is against me and need to get the staff ordered to get in time..

We will be building garden room with angled walls (due to the fence around it and to maximise space) that will be used as sauna (it will have separate small sauna room inside), gym that will also be used as man cave.
It will stand on concrete slab which we have poured couple of weeks ago, it is insulated below slab and reinforced.

So my main questions are:

1. Breathable membrane - a friend who is a carpenter and has been working with sips quite a bit will help me with the build, but mentioned that he has seen quite few examples where breathable membrane placed on outside of sips osb has caused a mould and even rot to the osb - I am thinking maybe it was because they did not provide air gap between wall and cladding? Or maybe sips do not need breathable membrane placed outside? For cladding we will have 25mm battens and fibre cement cladding due to the distance of the build to the boundary. Sips walls will be 100mm thick and roof sips 150mm.
2. I have read some posts regarding base plate condensation and rotting when stood on concrete slab - sips supplier suggested to place 700mm dpc course under base plate so to allow 300mm overlap on inside and outside of the wall - for some reason I think that this is on high side for the inside wall and will not allow the bottom of the wall to breath when each side of the wall has 300mm of dpc overlapping - or am I wrong here?
3. Firrings to make slope for the roof - sips supplier does not make them, again my friend only deals with full Sips kits at work where everything is already cut and ready to be fitted, in my case we will have to do them ourselves. Our top plates will be 45x100mm from which we are planning to make firings for the slope, however them being at 100mm width we are struggling to find a way of how to cut them as blades will not cut for full width, both side wall firrings and main wall which will have the highest point and firring slope to be cut narrow way of the timber seems to be causing issues.

Any advice will be much appreciated! I have added a design of the build just in case (dimensions have changed).


  • back.jpg
    54.4 KB · Views: 0
  • Dimensions 2.jpg
    Dimensions 2.jpg
    39.4 KB · Views: 0
  • front (1).jpg
    front (1).jpg
    48.8 KB · Views: 0

Latest posts