Opinions please - normal garage foundation or seriously over-engineered?

[kingandy2nd]

**Sorry for the rubbish pictures, but I’m leaving my house before sunrise and getting back after dark at the moment.**

I’m having my garage and utility room demolished at the moment, and it seems to have become a bigger job than expected for the chaps doing the demolition.

I posted the job on one of these trader websites, got 3 quotes and picked the middle priced one who also had plenty of good feedback. The guy quoted based on pictures alone without visiting.

The walls and roof was demolished without issue on day 1, but ...

...then the garage floor slab has become a nightmare for them.2 uncessful days with the breaker, and day 3 (today) they’ve had a digger with a spike and they’ve got about one third of the way across. The guy says he’s never seen anything like this slab, depth of concrete or the thickness of the rebar.

I don’t have any experience of garage foundations so don’t have a view of whether he’s right or this is just a normal garage floor?

Price for the job was £1.8k for demolition and waste removal. I’ve agreed an extra £300 to account for the extra waste from this thicker than expected garage floor.

The guys are nice blokes, a dad and son outfit, not some big firm. I’m not hard nosed and I wouldn’t expect them to make a loss doing the job, but equally I don’t know what should have been expected by them and what is really extraordinarily in terms of a garage floor.

Therefore I’d welcome the forums view on whether if this garage slab is really as unusual as suggested? Thanks

Before:

 

[John D v2.0]

It could well be that since it is attached to the house it was built off the same Foundation. And it could be that is a raft Foundation due to the ground conditions.
Raft is very thick with rebar because the ground may provide uneven support.
I would say a normal garage Foundation would be either a strip going down half a metre or a concrete slab thickened at the edge perhaps with some mesh in it.
Someone more knowledgeable would be along soon

 

[wessex101]

I agree, looks like a raft foundation and probably supports the entire house. You need to consult a structural engineer to make sure you can actually remove that corner of the raft or whether it will weaken the remainder.

When the "builder" hit that thick reinforcement it really should have rung alarm bells and they should have stopped work.

 

[kingandy2nd]

Thanks guys. The area is all sand so most of the houses are built on piles. The garage was built after the original house.

The garage has to come down to make way for the new extension which will be piles and ring beam.

 

[wessex101]

So you knew the house was built on special foundations and never thought to share that little snippet with us or your builder? I hope you've got deep pockets.

 

[kingandy2nd]

So you knew the house was built on special foundations and never thought to share that little snippet with us or your builder? I hope you've got deep pockets.

I'm sorry, as a non-builder I don't know what's important and what isn't. And I'm not sure there's any way to know how the garage was built without digging it up.

At the end of the day, the garage needs to be removed whatever it's going to cost.

 

[wessex101]

The builder probably based his quote on the garage having a standard concrete slab, so 1-2 days to break it up.

If he'd known the house was piled he should have allowed for a reinforced concrete suspended slab and ground beams. Now he can charge for an extra 2 or 3 weeks chipping away at it with a small breaker. Probably best to sit down and agree the extra cost now before it racks up anymore.

 

[kingandy2nd]

Thanks. Exactly why I was looking for views from people more knowledgable than myself. He's got the digger with a breaker on it now and making progress. As I said before I want to make sure I pay a fair price for the work and not hold them over a barrel based on the original quote.

 

[Leofric]

If you know the new extension will be built off piles and ring beams you have presumably already involved a structural engineer on the Building Regulations application. What was specified on the plans regarding the removal of the existing garage floor ? I would have a word with Building Control or your engineer before any more of the reinforced concrete is broken up or you might risk destabilising the house.

 

[OvertonPlumber]

Lets hope its not a cantilevered raft foundation. Possible the right wall of house was too near to a sewer?

 

[ivixor]

If that rebar continues through under the house, you have your answer. And you should start getting worried. You might want to check that before you go any further.

If it doesn't, then that's good news for you, and it means the garage was built on a raft, where rebar is standard. The SE doing your extension should have checked the existing foundation and determined if it could be reused.

 

[Notch7]

Im worried: the OP hasnt come back -has his house fallen down

 

[John D v2.0]

If that rebar continues through under the house, you have your answer

The garage was built after the original house.

The op has clarified earlier

 

[kingandy2nd]

Apologies for the slow response...been a bit busy lately!

We got there in the end - the old slab was removed over a period of nearly 2 weeks, but that's really because the demo guy was disorganised with diggers not showing up, other tools failing etc.

14 piles were input, some going down to 12m and then the ring beam and concrete done. All signed off by BC. All in all we've spent £12k to get this far.