Extending a garage base

[geoffbeaumont]

Need some advice from the wise ones on here - I need to replace my garage, which is delapidated and leaky. The plan was to demolish the current wooden structure, dig out the base excavate at the back and then build a new base and foundations 4x11m (the current one is 3.6x7m) with the drainage properly sorted and water supply, and then a single skin brick and tile building with insulation.

However, that's a wee bit spendy at the moment... Builders have quoted £50k inc VAT 🤯

So, I need to find a more affordable solution. I could go for an insulated steel building, which as well as being cheaper in itself, even with a fake wood finish, would only need a slab, but a lot of the cost is in removing the old slab and laying a new one.

Would extending the existing slab work? If probably have to stick at 3.6m wide, as I'm guessing adding a strip each side would be totally structurally unsound?

Our is this just a really bad idea?

With noting that we're on clay here.

[Stellaghost]

No reason why you cannot lay next to existing slab, dig it out and make sure you have plenty hardcore wacked in drill the sides of your existing slab 6 - 8 inches and knock some rebar in this will help it tie with the new slab and the old regards Stephen

[LiftedDisco]

As per the comment above, there shouldn’t be a problem to tie the new ring beam into the existing slab.

 

What quality is the current slab and is it reinforced?  What thickness?

 

Dig out for the extension / ring beam and then dowel in some U shaped re-bar into the side of the current slab with the closed part of the U extending into the new ring beam - fasten the open ends into the existing slab with resin anchor (note this cures really quickly!)

 

Install your re-bar cage or mesh for the ring beam and extension to the slab and then drill and resin anchor for your new holding down bolts - in an ideal world, I’d suggest having an above ground ring beam as this will give good water protection, preventing ingress but this would need shuttering and is a bit more involved...

 

Steel framed building of that size would be cold rolled, easy to build and far, far less than £50k!!!

[De Ranged]

It all depends on how well the original slab was done, it was common here for people to build the garage with a dirt floor (structural part was the Nib wall) then later on mix and pour there own floor 

Based off this i'd recomend doing a foundation Nib wall around the old slab so the beams of the new shed have a reliable foundation.... oh and this will let you see how good the old concrete is, if its good enough hammer drill in some rebar to tie to the new foundation if you are going to glue the rebar into the old slab 60mm deep is good enough if you just let the cement glue it then..... bugger I can't remember what the spec was, think it was a 16mm drill and 6mm bar, but it was 120mm deep and just mush the slurry in with the rod

[Retroanaconda]

Will you be over 30m² in internal floor space? If so then you need building regs and will likely need the base signed off by an engineer - particularly given your clay soil - and so you’re probably best to seek advice from one first. They may want strip foundations depending on the building construction and site conditions.

With the way building material prices are at the moment though I would be holding off on any non-essential projects as you’ll pay 25-30% more for it all than normal 

[landroversforever]

What state is the old floor in? Sister/BIL's place they've extended the garage and added ~1.5m to the length and width. The old slab was quite low so its got a full foundation on the extended sides, and then the whole lot has a 4" rebar'ed slab over the top of everything.

[landroversforever]

Also what james says... a lot of the costs at the moment are through the roof. Cement bags going from ~£4-5 some places round here they're £25-30 a bag at the moment! 😮 

[geoffbeaumont]

21 hours ago, LiftedDisco said:

Steel framed building of that size would be cold rolled, easy to build and far, far less than £50k!!!

£50k is everything, including demolition of the old structure and slab, proper drainage, etc. Basically everything bar electrics. So a fair chunk of it is the same.

Insulated steel building (just the actual building) would be about £17k.

 

21 hours ago, De Ranged said:

It all depends on how well the original slab was done, it was common here for people to build the garage with a dirt floor (structural part was the Nib wall) then later on mix and pour there own floor 

There's no nib so far as I can see - just a single row of bricks sitting on the slab with the wood frame on that.

[geoffbeaumont]

20 hours ago, landroversforever said:

Also what james says... a lot of the costs at the moment are through the roof. Cement bags going from ~£4-5 some places round here they're £25-30 a bag at the moment! 😮 

Yeah, I'd like to get it all sorted, but I think it will probably have to wait.

I can at least get the sheds sorted - should just be able to reuse the bases there, which will likely gain enough dry storage we can get rid of the storage units we're paying for at the moment.

[geoffbeaumont]

21 hours ago, LiftedDisco said:

What quality is the current slab and is it reinforced?  What thickness?

It seems pretty solid, if not terribly flat, but no idea if it's reinforced. Depth I can find out with some excavation - is currently level with the surrounding ground at best (yes, someone really did think it was a good idea to lay a concrete path up to the side of the garage - and I don't mean the base, either, it's a few inches up the wall...). Looks like it may already be two sections, but hard to tell until I clear some carp.

[LiftedDisco]

I don’t do anything that small (my last shed was 36m a 93m with 10m eaves height...) but you might want to talk to Murray Steel Buildings who offer cold-rolled steel buildings and are supposed to be decent prices...

 

They may also advise on what would be needed for ring beam or foundations...

 

[geoffbeaumont]

16 hours ago, LiftedDisco said:

you might want to talk to Murray Steel Buildings who offer cold-rolled steel buildings and are supposed to be decent prices...

I've looked at their site, but I think they only do fairly industrial looking finishes? This needs to fit in so either brick or wood finish.

[FridgeFreezer]

I expanded an existing slab and put up a steel garage at my old place. Worked lovely - it was a bit warehousey from the outside but that's because it was quite large / tall so anything would have looked big.

I dug it out and then got a readymix truck to come and pour it, saves a lot of labour and doesn't cost much at all.

 

Garage from Premier Steel Buildings, delivered as a flat-pack:

 

Going up:

 

Inside when there was room to swing a cat:

 

Added some trellis and grew climbers up it to break it up a bit:

 

 

 

[Arjan]

That looks nice !

[FridgeFreezer]

14 minutes ago, Arjan said:

That looks nice !

It's come out OK, the height was a compromise due to the back alley forcing the door size... basically if I could've driven straight into the thing and used a roller sectional door I could probably lop 2-3 feet off the roof height

As it is, the alley runs parallel to the door so I had to have a very wide door, which necessitated a large roller shutter diameter, which meant I had to push the roof line up to fit it underneath... annoyingly if I'd gone up another 6 inches I could've gotten the ambulance in  although I didn't own it back then - as it stands I might just be able to squeak a sectional door in and get the ambulance under the door, but whether it would be possible to park the damn thing in the space is another question 127's not being the easiest thing to manoeuvre.

 

Having walls / fence panels along 3 sides breaks it up, and the plants and trellis really help on the garden side. I don't know if brown rather than green panels would've been better or worse visually.

[geoffbeaumont]

Mine doesn't need to be particularly high (access is along the side of the house under a car port, so that limits the height of anything that can reach it anyway, and the vehicle door will be in the end). However, it's in full view of our patio doors so I won't get away with the industrial look.

Not that the current garage is exactly a thing of beauty...

[smallfry]

£50 k ? 😲 WTF

DIY I reckon £7 to £8k tops. Be generous and say £10k

3 blokes 3 weeks, OK again be generous say 4 weeks on £1k a week each.

Nice profit margin.

[landroversforever]

Digger/dumper hire, muckaway/skip, materials.... its all expensive and soon adds up. Garage extension I mentioned above was 2.5 8-leg grab lorries. and that was with one wall using the original foundation. 

[Bowie69]

Have you looked at self assembly log cabin style garages?

Just need the pad, and knock the rest together yourself with a big mallet. 

Lots of options, some do custom buildings: 

https://www.simplylogcabins.co.uk/wooden-garages-c49

 

[geoffbeaumont]

12 hours ago, Bowie69 said:

Have you looked at self assembly log cabin style garages?

Just need the pad, and knock the rest together yourself with a big mallet. 

Lots of options, some do custom buildings: 

https://www.simplylogcabins.co.uk/wooden-garages-c49

 

Not much cheaper than a wood finish insulated steel building for a similar size (in fact, given the steel one included assembly, not cheaper at all). The excavation and slab is where a lot of the cost is, especially at the moment.

[RedLineMike]

@FridgeFreezer what size / cost was that shed you put up?

[FridgeFreezer]

On 7/13/2021 at 7:06 PM, RedLineMike said:

@FridgeFreezer what size / cost was that shed you put up?

It's a long time ago now but it's 8m x 5m by about 3.5m ish, roller door is about 3.5m wide. Can't remember the exact money, but very roughly 5k delivered.

[Ed Poore]

£50k seems a little ridiculous, I've been pricing up doing my garage build and regretting not doing it last year because it would have been half the cost.

It's going to be roughly 28x28ft, 4m tall on the ground floor and then a double pitched roof above that. It's sunk into a bank so the initial plan (probably more expensive) was shuttered concrete walls on three sides and slab underneath. That was a 300mm deep footings in C35 with the rest of the slab 150mm deep, the walls were going to be 300mm thick. All with a ridiculous amount of rebar as per structural engineers arse-covering calculations.

Ball-park cost was going to be £25-30k at current prices, bearing in mind strutural steel has gone from ~£4-500 / tonne this time last year to over £1k / tonne and I paid £76/cube for C40 concrete September last year and C35 is now up to £120 / cube down here.

 

What about going a silage / farm building style - steel structure with blockwork or poured concrete between I beams. Once the brickwork / concrete is done then you can paint / render to whatever your desired finish.

[Bowie69]

That sounds about right for the concrete down this way too, had 1.2 cum a few weeks back and was £138.

Last year would have been £80.

For ground works, can you get a dedicated contractor/agri chap to come in? Probably cheaper than getting the building contractor to do it...

[geoffbeaumont]

Maybe, but parking it for now. Extending the slab and using a steel structure would have been okay, but the existing slab looks like it's already been extended, and if building control turned round and insisted we dug it out after we started we'd be in a sizable financial hole. I doubt we could prove to their satisfaction that the slab is good enough.