Garage conversion building regulations

Hello to everyone, I'm hoping for a little guidance please.
My parents have recently purchased a bungalow that needs the garage converting into a habital area. I've had 4 builders looking at it but only one has supplied a price to convert it, this i found very excessive, £10.000 in all.
I've viewed many of the threads on here and spoken to my local council for advice and sort of know what i need to do in order to achieve a nice conversion that meets BR. If i can explain the process i intend to follow perhaps as i go along i'll make very few mistakes.

I can split the conversion into 3 parts.
1. Roof
2. walls
3. floor

1. The roof, unfortunately the slope on the internal ceiling is quite excessive it falls by approx 14" from one end to the other, so i intend to have approx 3 courses brickwork to level the ceiling, hence raising the joists, allowing for a slight fall.
The BR gent advised me that a minimum of 100mm of kingspan would be required to meet current specs, this is to be applied on top of the roof boards then felted over (is this Correct) i was hoping that the kingspan could be fixed between the 4" x "2 joists. then plaster boarded plus finished.

2. The walls are single brick, i intend to apply a vapour barrier direct to the brickwork, then use 4" x 2" timbers at 450 or 600 centres then apply 100mm kingspan between the timbers, plaster board then skim.

3. The floor is concrete, i think a DPM 1200 gauge then 100mm kingspan and finally a suitable chipboard/wood floating floor finish.

There are two areas i have issues with, the kingspan on top of the boards then felted and the other is if i raise the floor by approx 118mm this creates a step up into the extension from the outside.

Can anyone advise me if they see any initial problems or offer any guidance on better materials etc.

Thankyou
Cannydanny

10k for a full conversion is not excessive.

It sounds to me like you have a bog standard half brick garage with a rudimentary sloping roof - just a little better than a pre-fab.

Have you considered that you may need internal foundations plus blockwork to support a new roof?

Having a chipboard floating floor is very basic and quite poor by building standards.

However, using kingspan to the walls and perhaps doing the same for a warm roof is on the right track, though 125mm is more typical for the roof and maybe more to discourage cold bridging through the stud walls.

If you were to put the insulation between the joist/rafters (cold roof) then you would need to put a thiner insulation board over the timbers before plasterboarding and vent the roof cavity.. the last one we did like that a few years ago had to have continuous venting along the soffit, holes in the rafters for 'cross ventilation' and mushroom type vents coming thru the felt at the top end near the wall abutment!. That might have just been our BCO tho.. lol

Might be easier with a 'warm roof'

This isn't a horrendous site, watch the U values though as they're out of date http://www.carryduffdesigns.co.uk/conversions/garage-conversions.html

Hi and thankyou all for your very quick replies.

noseall, The 10k was not for the full conversion, it didn't include any electrics and the quote was for raising the existing roof and insulation and re felting. although i now realise that raising the roof even tough its only by about a foot creates a problem as this would involve the area around the roof. sorry i should have been more exact with my details. As for internal foundations, i've spoken to both the Br and the planning dept at the local council and mentioned this but both were not concerned at all with this. As for The chipboard flooring, yeah wrong wording on my behalf, i deff use something else.

The brickie, Putting the insulation between the roof joists would be alot simpler but speaking to the bro this was a no go, your right a warm roof is the only avenue left open.

Freddynercurystwin Thanks for the link i'll have a look.


I've run into a couple of problems which may not allow us to carry out a full conversion, There's a lean too conservatory attached to the rear wall of the garage, raising the garage floor would mean removing the conservatory as the conservatory roof is only about 50mm above the door opening, so it seems it may be more difficult than first thought.

What are your thoughts on just carrying out roof and wall insulation and leaving the floor as it is, i realise this would not be to BR standards but this would provide an nice large utility room with plenty of room should my parents wish to put table and chairs in, there is at present heating in the garage.

Thankyou
Cannydanny

cannydanny said:

What are your thoughts on just carrying out roof and wall insulation and leaving the floor as it is, i realise this would not be to BR standards

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There are some situations where increasing the thickness of the floor/wall by adding insulation can create problems with change in levels, etc... In these instances, you may able to provide a balance and add additional insulation in other areas (e.g. wall and roof) to compensate for the limited or lack of insulation to the floor. However, I don't think you'll be able to comply if you're providing no insulation to the floor. Something is better than nothing.

If you were to look into this and therefore still complying with BR's, then you will need to get in contact with somebody who can carry out the necessary calculation, e.g. SAP assessor to carry out a "trade off" calculation.

Speak to your local BCO to see what they say.

cannydanny said:

this creates a step up into the extension from the outside.

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Do you intend having a door between the utility and the existing house? Or are you saying it will be accessed via the outside and it is here that you wish to avoid a step up? If so you need to just raise the local ground level in that area.