Building above garage not possible

[sparklewater]

We've just had our survey come back on the house we are buying and we asked them to check the integral garage as we want to extend above it.

Lots of other houses on the street have done it, so we assumed that it would be ok, just wanted to get the all-clear.

It's come back saying that it's a single-brick wall and unless the foundations are really deep, we'll probably need to knock down and start again.

Does anyone know what the price difference would be with that additional work? We wanted to get it done straight away but it looks as if we might have to save up and wait now!

At least £1500 per cubic metre. You have to factor in demolition. More in the SE and London.

You don’t want single brick walls holding up the weight of a building above. In structures, all weight is transferred into the ground. That’s what makes them structurally sound. So foundations must be of appropriate size for the building.

Thanks both.

Happy to do it properly and want it all to be safe, but it's the cost of the demolition and starting from scratch that I'm not sure of and can't find anywhere...

I'm afraid I don't know the exact details of a friend of mine built above a Single skin garage and certainly didn't demolish it. Wasn't a conventional build construction but you never know from looking at it now and it's a great addition so I wouldn't write it off completely without first investigating.

The single skin wall isn't so much a problem. Proving to the local building control that the existing foundations are adequate is the key.

They might be fine.

We did build above our detached garage and quite simply single skin garages with shallow foundations are not suitable for first floor extensions. How do you put double skin walls on top of that? It’s not possible. You cannot built habitable accommodation from single skin brickwork. So it has to be demolished and built up again. The demolition won’t cost loads but the building costs I quoted will be about right for foundations and rebuilding but more if finishes are above a standard spec. So if the garage replacement is 3m x 6m x 5m high you need at circa £130,000. Cheaper roof finishes, windows and diy from you will reduce this and your plans might not be 90 cubic metres either. The above is an example.

If loads of other houses in the street have done it might be on the planning applications so have a look at your local council website planning department and search by address.

My planning application just had "matching brickwork" stuff on it but my building regs stuff had all the steel measurements and load info. I didn't build over a garage though, sorry. The building regs stuff isn't available online, it is stored within the council.

If you get no joy from that then you could do one of two things, put a note with an email address on through the houses that have done it to ask how they did it or book to speak to someone at planning/building control to see how this was dealt with.

You usually dig an inspection pit and go from there, there may or may not be adequate foundations but until you dig you don't know.

We are almost finished our two storey extension - our garage was knocked down and we extended out to the side by a further metre - the size is now 4m x 7m - this was enough for a master en suite and a small bedroom/study upstairs. Downstairs a reasonable sized family room, a large utility and cloakroom. Our build cost was approx £75k with an additional 10k for standard/good quality fittings. Everything done by great builder. We live in Scotland so am sure price will depend where you are.

A house near us erected a steel frame around the garage which enabled them to build larger than the garage footprint, but it would have been cheaper and quicker to knock down the existing and redo the foundations apparently.
In the grand scheme of things new foundations don't take long and at least you can build the extension to modern spec (insulation etc) and install drainage if needed.

I should of course have said that £1500 pm2 is for all 4 walls but you don’t need that! So it would be cheaper than I indicated. Apologies.

Don’t think you need to knock down and start again, couldn’t you just have foundations checked and then underpin existing. Underpinning would be cheaper.

Interesting to hear that it's not impossible - I still think I'd rather assume the worst and then be pleasantly surprised if we can do it!

£130,000 is loads though, if it's that much we'll be waiting a while

what you can do is to redo ground floor & foundations & when you can afford it do the top floor & roof (we did this)

I've attached the floorplan of the property.

I make the garage section (the office/utility behind it is a more recent extension and has proper walls) just under 11m2, so assuming we go 5m high then it will be 55m.

So that would be about 60% the size of the £130,000 example. Which comes out at around £78,000. Which feels a lot more manageable/we can get it done sooner!

Look into timber build for building above the garage. A lot lighter. May still have to rebuild the garage, but worth checking in case.

Just had something come back from their solicitor saying they didn't get a buildover agreement for the orangery and it goes over a sewer. Argh. Will indemnity policy be enough?

It was built in 2014 so post 2011 when the regulations came into force.

Don't know why it posted the plans again

Just get a contractor to look at it. Where I used to live it was common for seperate garages to be knocked down and rebuilt when extending - so it can’t be a huge problem or too high of a cost.

@sparklewater - we've just done build-over sewer extension and the first port of call was the local water company (e.g. for us it was Bristol Water). You could call them today and explain, and ask what they'd advise in terms of next steps - perhaps retrospective sign off is possible? If so you'd want the vendors to arrange it at their cost.

TBH the build-over certificate itself wasn't a big issue, under £500 IIRC and they just came over and put a camera down the manhole to check the sewer was sound.

The main point of the permissions hss to do with foundations and putting strong lintels over the sewer - if the weight of the extension is resting on the sewer then it can easily crack and you'd end up with raw sewage leaking into the ground under your home - NOT GOOD! :)

But my bigger question is if they didn't do build-over, did they even have building regs sign off? Or is it a general DIY maverick "chuck up a building" affair, in which case you might be in real trouble...?

Thanks @WoolyMammoth55, that's really helpful.

It's a one-storey orangery so comes under permitted development and doesn't need building regs.

Next door have a complete two-storey extension along the length of their property and it runs along the same part of theirs property as well. So I figure they would have had to have building regs to ensure it was all ok.

I don't know about foundations though, of course. Annoying!

Would an indemnity policy cover us for all of this? From what I can see retrospective build over would be no good if there was an actual problem in the future..

Hi OP - our extension is under PD but we still have building regs sign off the quality of the work.

I'm no expert but my understanding is that planning approval is building control, but quality of work is building regs? They check for things like are beams correctly fireproofed, are extensions deep enough, etc. It's nothing to do with planning.

I believe that they should have had building regs sign off the orangery regardless of PD, and if they haven't, it's likely not compliant with building safety regs and you may have trouble insuring your home - general insurances, not specific to the build-over.

I've no clue about the indemnity I'm afraid, but FWIW we viewed a few properties with illegal extensions when we bought last year and they all would have been impossible to insure (and to re-sell, IMO). Good luck! xx

We had a single storey brick garage where we wanted a 2 storey side extension, and yes, it had to be demolished. We did manage to re-use the roof tiles though. £1500 to £2k per sq m is a fair price to work it out to, as a pp has said.

Oh thank you @WoolyMammoth55 - that has scared me.

Just frantically googling building regs now and found this:

"Orangeries are slightly different from a conservatory by using more brick in the construction and are usually an open-plan design leading from the main house.

Unless it has the same exemption as a conservatory, an orangery usually DOES need building regulation approval."

Right then, back I go!

Thank you @reedwarbler. Did it cost much more to have the original knocked down?

No, the knocking down amazed me with its speed! 2 men, a lot of bashing and drilling up of the original concrete floor and it was gone within 5 days - and loaded onto the back of a grab lorry the Monday after the demolition started. I don't know exactly how much it cost, but it's not a difficult or expensive thing to do. There's not much skill to it. The extension was considerably larger than the garage ( new bit is 42 feet by 11 feet), and also included a whole house refurbishment, (new doors, windows, boiler etc) a further extension at the front, all bits and pieces (kitchen, bathroom) and landscaping and it came in at around £140k in total all finished, which I think was a fair price, and it was 5 years ago now. If you are just doing the side bit I would expect it to be well under that, depending on size of course.
BTW, the disruption and mess is terrible!