Garage conversion costs

My folks have a large (50’ long) L-shaped garage, attached to their house, built about 13 years ago, with a pitched tiled roof. These days they are not so well; my mother is a paraplegic and dad has Alzheimers. So they are converting half of their garage into a groundfloor bedroom, so my dad can move downstairs. I thought this would be a straightforward and cost effective job. The plan would be to put in a dividing wall in the garage, knock out an existing window (which has a steel lintel), and make into a french window into the garden, and put in a fixed pane where there is an existing stable door. An existing window will be bricked up, and a door knocked in from the adjoining dining room.

The builder, who has done all the work for them over the years, including constructing the garage in the first place, has come in at £22k, which sounds a lot, as I was expecting ~£10k. This is a verbal quote based off what an architect drew up.

The Constructions notes are below. Does this quote fit with the notes below.

I’m guessing:

French Windows: £1000
Single full length glazed window; £500
Electrics: £500 (being a garage, there is also electrics in the garage, so its just addition of sockets)
Blockwork: £2000; gap to be bricked up is about 4m wide, so maybe 10 sq meter, or does it need to be blocked the full height of the garage, and not to around ceiling height
Boxing in ceiling: £500
Door from house and Iintel: £1000
Flooring: £1000
Plastering the room: £1000

So I am struggling to get anywhere near the £22k quoted, unless I am hopelessly out of touch about the cost of things these days.

Any thoughts?

Some of the re-work is more expensive than a fresh build because it takes longer and needs material removed from site.

All that insulation being added is expensive, and the garage would not have had habitable standard insulation. The floor could be expensive if the garage floor needed to be lifted to get the floor levels right with the correct insulation…

10K is a bit low, 22K is a bit high. But the builder needs to make a profit. The spec is good, and if it is done properly with a good finish in a decent time scale then it is just about worth while.

As an electrician, I can say that £500 for sockets is a rip off. Assuming the other charges are also as inflated, I would tell the builder take a walk. Do you have a Trusted Trader scheme in your area, perhaps one administered by the council? Local community social media may also be able to recommend a contractor. Good luck.

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May I suggest you obtain 3Nr written quotations from recommended local contractors ( your Building Inspector may be able to help regarding reputable contractors). Do not forget VAT at 20% unless your parents qualify for exemption due to their medical circumstances.
For estimating purposes I would say £1000/M2 of floor area for renovation works of this nature.

I’d agree with RichardFX about the extent of work. A non-inhabitable ‘shell’ being converted to an inhabitable room or rooms must be built to new-build standards to pass current building standards inspection. These days floor, walls and roofs have to be insulated, all of which takes plenty of work. As for making it habitable, there appears to be no mention in the quote for heating as far as I can see.

It seems expensive to me too. I would definitely get 3 quotes. We had 4 for a new roof, giving the same spec to each one. The quotes we got back were from £11.5k to £19k, do there is always a big variation. We are going for the second cheapest at £12.5k as the cheapest did not fill us with quite as much confidence. Anyway, get a couple more quotes and good luck.

Thanks for replies. Its not going to be possible for the house owner to get furthe quotes, there is a pressing time factor. The “breakdown” is just my guess. I think they want wall mounted eectric heaters, rather than adding onto their central heating (combi boiler).

It sounds like the quote is within the realms of possibility, and I know this builder (local from the village) does work to a high standard. The neighbours used builders for an expensive extension who appeared to be complete cowboys. Better the devil you know.

Thats all from me.

If he’s a trusted builder and his work is to a high standard then get him in.

I’ve got a trusted roofer, he’s done work mainly to my son’s roof, completely re done it using the original tiles plus replacing any damaged. A few timbers were rotten and the felt was shot.
He’s worked on it in 3 stages for him to soften the blow of paying for it. I never did get quotes from others as I’ve seen the work he’s done for neighbour’s then mine. I thought it was a very reasonable price for what he did to all.

Currently in the process of getting a quote from our trusted local builder to convert half of our double garage to a craft room for my wife. The garage part does need to be fireproofed to the habitable section. According to my builder the dividing wall can be stud work, insulation and plasterboard providing fireproof plasterboard is used.

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Saz, I’m probably teaching my grandmother to suck eggs here, but please ensure that any/all plans get approved by your local council prior to any work being done. Best regards. Having been my sick and elderly parents’ sole full-time carer for 15 years I can appreciate the stresses and strains you’re under to some degree.


much the same as ceilings in garages that have habitable space above. Double boarding and skim was the order of the day, not sure now :thinking: Blockwork might be as cheap, only plaster the workroom side?

That’s how my garage was done forty years ago, our bedroom is above it.

The problem is not so much the plaster board failing in the fire - it’s not flammable; but the nails/screws melt and the board just falls off the joists. So the lower layer of board protects the fixing in the upper layer. Hopefully two layers skimmed give you the half hour you need to get out safely.

Top class plasterers can make the job look fantastic, and they’ll use the correct stuff.

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Bosh bosh, skim skim, Loadsa Money!


Have to agree about getting planning. This was posted to another forum that I’m on:

I’m pretty sure you’re not allowed to just convert a garage into accommodation. The planning permission for your house would have been based on an amount of off road parking being both your drive and garage. If you convert your garage this breaches the planning for your house. I know most people don’t use the garage for their cars, but a whole load of people around me did exactly what you’re doing got caught, fined and forced to convert it back and then inspected. If you do it you also have to comply with building regs with things like fire doors ventilation and level of insulation, it can also impact your council tax banding upwards.

If you sell your house you will either need to convert it back or it will show up on the search, which means the council find out about you…

The bad news is you used to be able to do it as long as you made another off road space, but block paving over gardens to make extra drives is also becoming increasingly problematic, so your application will probably get refused

the people around me ended up getting caught when someone moved into the area and commented on the lack of on road parking, they tried restrospective planning, all refused, then the loophole about if you build something but there is no challenge but that got blocked by it being a concealed development, all with more costs, angst and i think they even had to pay the council to come and inspect it after it had been put back, three years later they still get random inspections to make sure it’t not returned


Don’t know about the parking space situation but we currently have a 4 bed with double garage and driveway for 4 cars. Even losing the whole garage we will have room for 4 cars. Other houses on the same estate have 5 beds and only room for 3 cars or 4 beds and room for 2 cars.

The original house in question was built in the late 1940s with a built in single garage. That was converted ~20 years ago, with no issue. An additional garage was built in an area previously occupied by a workshop. The conversion in discussion refers to about one third of the garage, retaining a generously sized single garage. A private driveway can accomodate 5-6 cars. For the avoidance of doubt, Building Control people are involved, so no issues there. The builder has just come off another job, converting a whole garage for another paraplegic 4 doors down.

As per central government advice:

Planning permission is not usually required, providing the work is internal and does not involve enlarging the building.

If your intention is to convert a garage into a separate house (regardless of who will occupy it), then planning permission may be required no matter what work is involved. We advise that you discuss such proposals with your local planning authority to ensure that any work you do is lawful and correctly permissioned.

Sometimes permitted development rights have been removed from some properties with regard to garage conversions and therefore you should contact your local planning authority before proceeding, particularly if you live on a new housing development or in a conservation area.

None of this applies here.

The house will be sold when they are dead.

Well, I suppose that’s one way of saying - “Thanks for your concern guys, but everything’s in hand”.