Detached Garage Conversion Plans with Drawings

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I'm planning a conversion from a detached single garage (no building regs required) to an office space (15.8m2). First time I've taken on a project of this size and want to make sure all the stud-work and flooring is as it should be before commencing, especially concerned about damp as anyone would be at the crucial stage.

I've drawn out two views, one from the top - showing the various 'layers' of stud-working going into the wall and another for the floor view.

Wall
The layout is standard apart from an brick stack which I want to hide in the stud work. I'm not at home right now so can't measure it, but from memory I'd say it protrudes about 15-20cm from the wall. I've shown in the diagram how I plan to wrap a damp-proof membrane, then plaster board over it. I don't think there'll be any space for insulation (perhaps insulated plasterboard will need to do here).

There will be a secondary stud-wall acting as a service cavity as I don't want to chip into the rigid insulation for socket boxes etc which will be forming the vapour barrier (foiled faced with taped gaps).

Sorry I don't have the measurements, I'll have those over the weekend which will mean I can exact the drawing to scale.

Stud work drilled into to concrete floor.


Flooring
Concrete floor already in-situ, but cannot confirm of a DPM exists under the concrete block so will be adding another layer of DPM followed by a thin layer of insulation with a foil face front to act as a vapour barrier then 22mm chipboard for flooring. Finally, laminate flooring.

No screed here; it's tiny surface area and don't feel too confident with the stuff.

Under floor heating was suggested but not too sure about the specifics on where this would go in my set-up (or even it's effectiveness - heat loss etc).

stud wall view.JPG
flooring view.JPG
 
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Google ‘garage conversion celotex’ and you’ll find their very useful advice on how to do walls with battens and insulated plasterboard which is of minimal thickness. If it were done with building regs the floor would need 75-100mm pir insulation which, if you have the headroom would be a good idea. If done under a permitted development application and building regs it would be official and add real value to your property for the spend needed.
 
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Google ‘garage conversion celotex’ and you’ll find their very useful advice on how to do walls with battens and insulated plasterboard which is of minimal thickness. If it were done with building regs the floor would need 75-100mm pir insulation which, if you have the headroom would be a good idea. If done under a permitted development application and building regs it would be official and add real value to your property for the spend needed.

I'm familiar with the insulated plasterboard and will look into what Celotex provide that's different. I just felt that there could no way be the same level of insulation with the thinner board compared to the above plan. The brick stack in the middle of the wall also means that I'd have to stud around it as the much thinner studding wouldn't come flush with the stack. There's most likely going to be bookcases along that wall so having them all flush against each other is important.

I checked with them and they're happy for me to continue without a need for an application; as it's exempt which I'm pleased about as it means no obstacles or delays etc (although it may increase property value)
 
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I want to add a second layer of foil backed insulation as the vapour barrier that needs to be screwed onto the studs so even if the studs were deeper they wouldn't be accessible via the VB. So adding that service cavity helps maitain the insulation and the VB and helps me route wires without puncturing it.
 
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Permitted development application doesn't cost anything & fairly quick as if going to the expense it adds £ value to home (Building regs fee is applicable of course) but if not then there are no insulation regulatory requirements so whatever you do will be fine but I'd insulate the block pier regardless. On that basis my comments would be that the cable void eats up valuable internal room/space and not really necessary. You could vapour barrier with foil tape on joints of first (and second) insulation foiled PIR layers. Run cables inside batten edges & cut electrical boxes out of secondary insulation layer then tape them over, then screw through PB & insulation to battens. Consider how the ceiling is insulated as you don't show that.
 
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Neither apply in this case as it's exempt, but I understand your point. After doing some measurements, it turns out it will be insulated via the vapour barrier insulation (the stack is smaller in width than I first thought). It's possible that if the main insulation is taped up to the battens, I may not need the second VB insulation, but I need to think about it a bit more as the additional layer of insulation may be beneficial given the single leaf structure.

How would you run the cables through the batten edges - these would have been covered by the second layer of insulation. Are you saying I should run the cables along the front of the battens, add the second layer of insulation, then tape around where the cables come out?

Ceiling insulation should be straightforward - mineral wool type insulation most likely.
 
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Yes because if you sold your property regulatory compliance adds £ value. The more insulation the better but not crucial if not complying. Either run cables around floor and go up (leave battens short of floor to do this) or come down and go back up to the ceiling (notch out battens if you decide to go across). Along side of battens or channel into insulation and foil tape over. Record runs for future reference with photos and measurements. Your electrical plan would probably be best reviewed certified electrician.
 
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I've done some calculation and its best for me to use 75mm for the main stud work with 75mm insulation inbetween the battens and maintain the second layer of insulation as a vapour barrier. The brick stack is 200mm from the wall.

After the 75mm stud work, I'll add 30mm barrier insulation which will leave the second service cavity which I've decided to keep which will be 50mm after the second barrier of insulation. This will now mean the second stud work is 30mm proud from the brick stack which is perfect for me to slot in 30mm of insulation in front of the stack.

Are the IKO PIR boards as good in performance as the other brands: https://www.selcobw.com/products/insulation/cavity-insulation?p=2
 
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It’s all pretty much the same you might find small variations in their spec sheets but nothing to get excited over
 

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