Yes, £56,000 sounds high for a garage conversion, but with today’s costs, it's not unusual especially with plumbing and a full shower room. Your £40k ballpark expectation is realistic for a well-done conversion without high-spec finishes. But prices have risen, especially since 2021, with material and labour costs surging. Still, you can probably save money by buying materials like tiles, sanitaryware, wardrobes and flooring yourself, and hiring your own tiler or flooring fitter instead of going through the builder for everything.

• Ask for a detailed cost breakdown from the builder line by line. It may expose areas of markup or ambiguity.
• Get quotes from 1–2 more builders for comparison.
• Ask to supply some of the materials yourself many builders are open to this.
• If you’re confident, subcontract tiling and wardrobes/flooring to save.
• Don’t compromise on insulation, heating, ventilation, or structural integrity just to save long-term comfort and compliance matter.
• Consider a Modular or Prefab Solution that can be integrated if possible

Companies who creates prefab to be integrated in house already a lot in UK like HUSK,Blue Bee Annexes, SupAlign Garden Buildings, Pegasus Garden Rooms, Composite Garden Studios

All start £32,500 + VAT you can check their product and unit specification that fits your need and perfected the interior or finish gradually overtime

Focus on the functionality due to urgency rather than trying to achieves perfect integration

Here’s a suggested way to test whether prefab could save you money / stress:

1. Measure your garage carefully (internal dimensions).
2. Get quotes from a couple of the prefab companies above for a unit that fits those dimensions + Base price + Cost of delivery + installation +Timeframe to install + required features (shower room, heating, radiators, insulation, doors suitable for mobility) + Customisation options (e.g., wet room, insulation level).
3. Compare to your builder’s quote, looking at the difference in cost, time, and disruption.

If prefab + base + utilities + finishes ends up cheaper (or similar) but faster and less hassle, it might be a better route.

@Angie. Thanks for the comment. I can’t get my Mum to agree to a lift because that makes her feel old, but a downstairs bedroom does not.
Luckily she can afford it and being pragmatic it’s still cheaper than moving house.

@Devyra Ateier. Thanks for the message. I’m not sure the prefab route sounds any more cost effective. However my research suggests that the garage conversion will add as much to the house value as my mum spends so she might well just have to bite the bullet.
It would however be interesting to hear from anyone who has done the same conversion recently so that I can sense check the costs.

Hi Jonathan, lifts cost about £20,000 so not cheap, but a much easier option if you can convince your mum to have one!

Hi Jonathan

There are quite a few articles online. This would suggest you’re at the higher end (excl bathroom) but not unreasonable? Where in the country is your mum? I assume windows were included in the quote? I must admit I’d struggle getting this in on budget for your extra costs like sanitaryware etc! I’m not sure if i’d do an ikea hack for wardrobes (unless not fitted), fitted are not cheap!

i assume the quote is from a tried and trusted builder?

https://www.myjobquote.co.uk/costs/garage-conversion-cost

@Sonia. Thanks for the message.
I can’t persuade Mum to get a lift and I was quite pro the idea because I think as soon as she has a downstairs bedroom she will stop using half of her house. But being pragmatic Bungalows for the same price are half the size of her house and you have to remove a lift and make good when you eventually sell so it’s lost money- but the garage conversion should add as much as she spends to the sale value.

@Minnie101 thanks for the message. There are a lot of these sites that say converting a double garage should be £25k+
In Mums case she also wants three windows which involves keying/bonding in the bricks which adds slightly to the cost (+£1,500). There is no personal door to the space currently so there is an additional cost there (+£1,500). I’m aware that some additional prep work is required for the soil pipe (+£1,500). So I was expecting it to be about £30k plus the cost of the en-suite which I estimated at £8-10k, plus wardrobes and flooring. So I was really expecting it to come out at early £40s so it’s been an eye opener for me.
She lives in Gloucestershire so there shouldn’t be any weighting in cost like you find in London. And I would have been worried about bad faith tradespeople had she not had three similar quotes. One of the builders seems very attentive so I think she knows who she is going to use I’m just trying to sense check the quote.

Johnathon, I know you said your mum ‘can’t face moving’ but a move to a bungalow sounds a much more sensible idea both financially and emotionally than having to put up with the building noise and upheaval that a conversion will certainly bring.

@betty boo thanks for commenting. I don’t agree because all the available bungalows need everything doing but by contrast the garage conversion is limited disruption.

So have you got a breakdown of all materials vs labour?

Am i right in saying some parts of Gloucestershire vary quite a lot in house prices etc? If she’s in a more expensive area have you considered builders outside of the area?

i hate to ask this but have you been present for the quotes? I had some builder last year trying to quote me 65k to dig up a concrete drive (3 spaces), replace with gravel etc (me buying) plus knock down and rebuild a wall

There may be some saving in sub-contracting but who will manage the trades?

Call me cynical but i might also worry a little if a builder was overly attentive!

@Minnie- since I live 200 miles away I can’t be there to manage trades. I think that’s the builders job. But there is every chance we will get someone different to do the shower room and there is an excellent company who think will be doing that.
You make a good point about trying a builder from further afield.

Is the builder willing to project manage if you find the sub-contractors? I think given how far away you are it would be much easier and less stressful for the builder to sub-contract but just stick with your bathroom co for 2nd fix

I‘ve only had a 1 second google and I don’t know your mum’s circumstances but it might be worth looking into whether the conversion qualifies for VAT relief

Good luck!

https://www.gov.uk/vat-builders/disabled-people