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Building over garage - how much roughly...

(18 Posts)
Karbea Thu 17-Nov-11 19:03:37

we have a double garage about 3ft away from our house but next to it, small alleyway between house and double garage. iykwim.
Wed like to build an extension over the garage but dh thinks it will cost thousands and thousands... So much that it'll stop me being able to give up work when we have children.

I think the alley would just be used for storage and upstairs I'd like a bedroom and unsuite.

Any really rough ideas of cost, we are in Buckinghamshire.

Thanks so much smile

sunnylabsmum Thu 17-Nov-11 19:08:13

we have a chalet bungalow with double garage next to it and we are having an extension over it. Its actually 3 garage widths because of the pointed roof- this will give us an extra 2 large bedrooms each with an ensuite and also a study area. We are actually demolishing the garage as the foundations might not be good enough and we can also get a utility at the bcak of the garage. Our architect thinks our budget of 60K is ok (also includes a remodelling other parts of the house)

SoupDragon Thu 17-Nov-11 19:10:14

I think the problem is often that the foundations of the garage are not sufficient to support the weight of an extra floor and thus the garage has to be demolished and rebuilt, as Sunny said.

Karbea Thu 17-Nov-11 19:23:37

Oh ok, dh has been saying £150k.

Our house sort of looks like a chalet bungalow, upstairs is in the eaves. So hopefully cost will be comparable.

Thank you smile

Yorky Thu 17-Nov-11 19:51:48


When I told someone we were looking at 50k for the extension we want they told me you could build a house for about 70k!

Karbea Thu 17-Nov-11 19:57:57

Really? I wonder where he got that figure from, the estimate to rebuild our house from our survey was £200k I think, but I always thought those amounts were a bit made up and you couldn't actually build a house for that much...

vinegarpuss Thu 17-Nov-11 22:05:50

i'm not in Buckinhamshire but we were told by our architect to budget for £1000 - £1500 per square metre for our extension (excluding interior finishings)

Karbea Thu 17-Nov-11 22:35:52

Umm double garage is 5.79m(19'0'') x 5.49m(18'0''), so what would that be in square metres?

Fizzylemonade Thu 17-Nov-11 23:05:33

you just times the length by the width so in your case 5.79 X 5.49 = 31.78 so call it 32sqm. The normal is £1k per sqm so £32k but that is without anything in it. You have to budget in for electrics, plumbing and the cost of the bathroom etc.

You can build a house relatively cheaply but the sale price would be much much more as people want a profit at the end of the day. I could not believe the rebuild cost of our house when compared to what we paid for it sad

Fizzylemonade Thu 17-Nov-11 23:11:27

Best thing to do is get a builder round, he can give you a rough idea and hopefully recommend an architect who can draw up some plans.

If you are any good with a bit of maths then you can draw your own plans. I did this for my garage conversion (double garage same size as yours converted into a playroom last year) and the kitchen extension which will be hopefully done in 2013, saving like mad. I gave this to the architect and he basically copied it but he did all the paperwork for the planning application.

For scale drawing I use 1cm =20 cm in real life so 5cm on paper would be 1m. Meaning your garage would be drawn as 29cm x 27.5cm then add in your passage way.

drcrab Thu 17-Nov-11 23:16:45

I showed my architect husband your post and his answer without looking at other posts was 'allow £1000-1500 per sq m for cost'.... Which is in agreement with previous poster!!! smile good luck.

sunnylabsmum Fri 18-Nov-11 17:07:25

We got a few architects around as we had an unusual house and wanted a wow factor with the extension. We are replicating the triangle point from the chalet bungalow with the extension and having a wooden frame to speed up the build time - plan is 20 weeks. The architects we chose have had some brill ideas and like the challenge of doing something different. Some of the architects we contacted were not as imaginative. We are based in cambs

yodpet Sat 11-May-13 19:54:24

I shall have my garage converts into bedroom.Next to the garage is my studio where the builders will knock the wall connect the bedroom to the studio.My studio has bathroom with shower and WC and also has a big conservatory. Those 3 rooms are damp and tiles started to come out. I decided to refurbish the whole studio. There will be a proper job with well insulation. The builders estimation is £25,000. I will have to pay for the carpet, new shower and toilet and sink myself. There will be 4 builders, and will take 5 weeks. They intend to finish in 5 weeks as they already have committed to build houses in Watford. These builders are friends of my friend's son who is a plumber. I have known them since they were 17 and now they are 33. Is the price is right? Neighbours keep asking questions as I am a widow and they think I will be rip off. These guys have done so many things in my house and never let me down. What do you think?

MrsGrowbag Sat 11-May-13 23:37:00

fizzy , the reason there is such a huge difference between rebuild cost and original purchase price of house is because of the value of the land. If our house burned down tomorrow, the rebuild cost would be approx £200k which is much less than the purchase price as we already now own the land.
We have just had an extension built, and all the quotes we got were in the region of £1200-£1400 per square metre for finished / completed build. Ours worked out at £1400 in the end. Ours is single storey, we were advised that next floor up would only be around £700 per square m because foundations and roof are part of build even if it's only single storey IyswIm.

Potterer Sun 12-May-13 10:38:40

As this zombie thread has been resurrected Karbea did you get any further with this?

Yodpet, I assume you are London based which does unfortunately raise the prices.

I had a double garage converted and retained a store room at the back. So the builders had to build a wall across the entire 2 garages. The two doors were changed to windows, I had 2 radiators put in, loft hatch boarded up, new loft hatch created, door knocked through from the hall into the garage. Laminate flooring (as it is the children's playroom I needed to let them paint/playdoh/run riot) and this cost me £11,500 but then I am in Yorkshire.

I am mid kitchen extension, it is working out at £1200psqm for the build part of it.

My main concern for you Yodpet is that if the go over on timescales they will probably start work on the new builds because that is far more lucrative than your build, so yours would be finished on weekends and evenings. That is just my gut feeling. Also because you haven't had any other quotes you can't compare your builders to anyone else.

As you have said, you know them, they have done work for you before and you have been happy, so me personally, I would be happy with that. My builder is laying my patio, I know his weekly rate, I haven't asked anyone else to quote me because I have seen him build my extension.

Karbea Sun 12-May-13 10:44:11


Yes we did, we've had planning agreed and I'm writing the builders spec at the moment. I still think we will end up spending about £175k, which is ridiculous! I think the building costs will increase the value of the house by about the same amount, so we should end up with a nicer house, and not be out of pocket.
Once the spec is done we will go to tender with 3 or 4 builders.

yodpet Wed 15-May-13 10:31:45

Thank you very much Potterer. I also asked my neighbour who has his garage done. I told him the quotation and he said it is reasonable. I also have had a email confirmation from the Haringey Council, customerCareTeam, said I would not require planning to convert garage into habitable including the conversion no permission would be required. I mailed this email to my solicitor already. To the appearance of the whole house, actually nothing will be changed even the space of the house. It is going to be exactly the same, except the garage door which will be like other neighbours except my next door. The garage is at the moment so damp that the painting is peeling off. The rest of the work will be absolutely internal work behind the door of the garage. The builders will arrange the Building Control Officer to come and inspect which of course that is another expense. I am doing this because my son and his girlfriend can live downstairs and save the money to buy their flat in 2 years time. They are renting a flat costs them £1,600/month. They stay with me free only to pay the 25% of the council tax. This is all parent can do.There won't be any kitchen as they will come upstairs to use the kitchen in the house. I went back to the Haringey council, planning department, talked face to face to the officer and he also said I do not need planning permission. What else I require to do so.

yodpet Wed 15-May-13 11:02:59

I must say I am hooked with Mumsnet now. Everyday I will read or ask advice and I always get answers. Before I joined the Mumsnet, I thought this web is only young mums. I am a widow and have been only a housewife since I married in 1975 and now a pensioner and non English and I managed to chat on line with people in English. If I do make mistake in English, please do understand me.

Any more advises on converting garage are very welcome please. I will also knock the garage wall to get into my studio where there is a small toilet and shower there, a tiny shower room.I actually asked my lawyer neighbour about this and he said this is internal work. he also knocked the wall in his house to make a tiny room for his son. Do you think I gather enough information, just to get garage change. The garage is so tiny that I drove the car in and broke the mirrors. Since then the garage turns to be a junk room.

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