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Garage conversion floor question
Hi. I am planning to convert 2/3rds of my detached single brick garage to an office. The other 3rd I would like to keep as un-insulated storage. The total dimensions of garage is 5.6m x 3m internally. Currently floor concrete slab to roof trusses is 2.16m.
Firstly as I read it I don’t have to get building control involved as it is not going to be converted into a bedroom. Is that correct from experience? Based in Devon
As I haven’t got much height I plan to not insulate the floor and just use a paint on dpm and put down some laminate. Is this advisable or would 50mm insulation board. 18mm boards then the laminate be a much better option?
If I am not getting building control sign off as it’s not a bedroom what thickness of insulation board would be suggested for walls and ceiling between existing rafters.
Thank you for your help.
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7 Replies
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Speak to building control
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It’s a change of use so needs building control, it’s what I do for a living, your insurance will be invalid if you don’t use the proper channels. Not worth it, will cost you about £700
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Mine is an office and I still got building control approval so I don’t understand how you think you can avoid building control.
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Realistically building control is required as it’s going to be a habitable room.
If you want to take the risk of not going with building control sign off, that’s your decision but if you want it to be a room you can use properly in all seasons, you are going to need the same level of insulation as they would require anyway.
Think about it, you need to build the stud wall, insulate all the other walls, sort the electrics out, get a heat source in there.
Time you have done all that, you may as well have done it properly and had it signed off.
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Ideally you should have building control and would always advise it BUT I know a lot of people who just convert it for an office then by studding the walls insulating them and insulting the ceiling put up a partition wall and when they moved simply took the studded wall down
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I am currently converting my garage. I think there are certain criteria that determine whether you need building control or planning involvement. Things like you said bedroom and whether you are putting heating in. I would definitely recommend you speak to building control and planning, they are really helpful and can tell you what to avoid or include to avoid planning permission and building control.
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Good questions – this catches a lot of people out
A few key points from experience:
• Building Control is required if you’re converting any part of the garage into a habitable space, including a home office. It’s not limited to bedrooms only. Once it’s heated, insulated and used regularly, it falls under Building Regulations.
• Keeping 1/3 as uninsulated storage is fine, but the office part will still need to fully comply (fire separation, insulation, ventilation, electrics, etc.).
Ceiling height
• 2.16m is tight but workable. You’ll want to avoid unnecessary build-ups where possible.
Floor
• Painting the slab + laminate is generally not recommended for a habitable room — it’ll be cold and can lead to condensation issues.
• A thin insulated build-up (e.g. 25–50mm PIR + 18mm T&G) is usually a much better balance between comfort and headroom. There are also low-profile insulated floor systems worth considering.
Walls
• Typical upgrade would be 50–75mm PIR internally (with vapour control layer), depending on space and target performance.
Roof
• Between rafters, usually 70–100mm PIR with a ventilated gap, or a hybrid solution if depth is limited.
Even if you weren’t seeking Building Control sign-off (which I’d strongly advise), following these standards will make the space far more usable year-round and protect the structure.
If you’d like, we can help with a compliant detail strategy, drawings for Building Control, or a quick feasibility check before you start — especially useful with limited headroom.
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