The definitive single skin Garage conversion advice thread?

Discussion in 'Builders' Talk' started by TK90, Aug 17, 2021.

  1. TK90

    TK90 New Member

    Hi,

    There's tons of posts on this forum relating to the conversion of a single skin Garage. I'm finding it difficult to find a fairly definitive answer, as I'm not sure if info is outdated, or which to go with!

    I'm converting half of my garage into an office. The room is of a reasonable size, but height is against me and any insulation on the floor or roof needs to be absolutely minimal. There are no damp issues in the garage and the garage has a concrete floor.

    1. What products should I use to insulate the walls?
    2. What should I use to insulate the floor (absolutely minimal depth for max insulation)
    3. Should I use 4 X 2 or 3 X 2 for battens? Or should I build a full stud wall structure
    Advice is much appreciated. Going snowblind to rock wool, insulated plasterboard, damp proof course etc!

    Thanks so much !
     
  2. Jimbo

    Jimbo Screwfix Select

  3. TK90

    TK90 New Member

    Thanks.

    With regards to the walls. Am I right in thinking insulated plasterboard is the way to go? Something like 55mm thickness? 2 X 2 battens to the wall, or plasterboard adhesive dot and dab?

    Thanks again.
     
  4. Jimbo

    Jimbo Screwfix Select

    What is outside - is it rendered? Or brick?
     
  5. TK90

    TK90 New Member

    Outside is just brick. Single skin.
     
  6. TK90

    TK90 New Member

    Worth noting, although the room is a decent size, I'd still like to maximise the space, so thinner the better. But, I need to be able to work in there (with a radiator) through winter.
     
  7. Jimbo

    Jimbo Screwfix Select

    Problem obviously is the moisture ingress. A vapour barrier is needed. The general gist is a layer of foam and a layer of plasterboard - others will know more than I about the vapour control on the walls.

    How is the ceiling constructed?

    Also - bear in mind that this will end up being a very low thermal mass structure. That is to say, it will heat and cool quickly. This will be an advantage if you don't leave it heated on a Monday morning but likewise if the sun comes in through the glazing it may get too hot quickly as well.
     
  8. TK90

    TK90 New Member

    Is there a vapour barrier built in to the PIR insulated board?

    The ceiling is a flat roof with joists that I was going to insulate between, then plasterboard (or insulated plasterboard over.

    Yes agreed - it's never going to be perfect. To be honest, it's about getting a space that's workable for the short term and doing it in a way that won't break the bank.

    There's some large glazed doors that will be open in the warm weather and a radiator that will be on in the morning on working days. Completely understand there's compromises I need to make.

    I guess I'm looking for what the best bet is!
     
  9. Jimbo

    Jimbo Screwfix Select

    For the ceiling, use a standard rockwool between the joists but be sure to leave 50mm at least clear to the deck. Then use insulated board or kingspan/celotex sheets across under it, tape the joints, and use expanding foam to for a seal around the perimeter of the room. Then plasterboard over the top of the insulation sheets.

    Whilst the thermal resistance numbers will look better using foam sheets between the joists, this depends on an absolutely perfect air-tight seal between the two layers and the roof void. In practice it's far easier to get the structure to perform using rockwool between the joists - even just a few inches of it - and the foam sheets under that.
     
  10. stevie22

    stevie22 Screwfix Select

    Are you trying to comply with building regs or just make it reasonable?

    Even 25 insulation on the walls will make a huge difference and a thick carpet underlay on the floor.

    Go to town on the roof with glass fibre: this is the easiest, cheapest and most effective area to work on. 270 of glass fibre will match code but you could go more
     
  11. TK90

    TK90 New Member

    Thanks. Not complying with regs. Hoping for a tidy temporary solution to get me by for a couple of years. Although, if it gets some use then it's one of those things that may end up there ten years. Thanks for the advice. When you say 25 insulation, do you mean kingspan or similar?

    Thanks
     
  12. Jimbo

    Jimbo Screwfix Select

    Yes, the first inch has the most impact. The thickness of glassfibre in the roof will depend on the joist size as it's a flat roof, noting the ventilation requirement.
     
    TK90 likes this.
  13. stevie22

    stevie22 Screwfix Select

    Sorry OP: missed the flat roof.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice