Ballpark slab costs: 12mx9m?

[Pabbles]

I'm struggling a bit here and hoping for some rule of thumb guidance.

 

I've had 5 formal quotes for a steel outbuilding (for a private workshop not for sleeping accommodation), which are OK. But only one company included a price for laying a slab and it seems bonkers - the rest want me to arrange it in advance.

 

I'm not quite ready to go to a groundworks company for a formal quote (there's a load of unrelated work to do on the site and I'd want them to quote for the lot in one go) so wondered if anyone could give me a rough guide as to what to expect on the slab laying in isolation?

 

The slab will be 12mx9m. 200mm thick C20/25 concrete with steel mesh (there's a vehicle lift going on it). The ground is untouched, perfectly flat lawn and there is >2.5m of free space all around. It is accessible for heavy plant and a mixer can back right up to it (over the grass).

 

I know I'll need about 27m3 of concrete (plus wastage) and I had one price (haven't tried to get competitive yet) of £3225+VAT. I know there'll be the costs of the hardcore and mesh, shuttering, etc and that the labour involves digging out, disposal, hardcore base, compacting, shuttering, laying and float.

 

I wouldn't expect anyone to try and work it out exactly but was hoping that someone with relevant experience could give me a very quick steer as to the sort of prices I should expect for the whole lot in NW England? Even if its only accurate to the tune of +/- 25% it would give me a good jumping off point while I do these early costings.

 

Thank you.

 

 

[Conor]

Similar size and spec to our floor slab, ground works, drainaged, stoning etc were 4k... But that was a lot of digging...

Shuttering and mesh laying was two guys for nearly a week. I think you'd be looking at £8-£10k.

[PeterW]

12x9 at 200mm is 21 cubic metres of concrete, if you then said you wanted to dig down a further 150mm for hardcore then it’s 40 cubic metres to dig out. Adding bulk up that is probably 60 cubic metres of muck away.

 

Using spons or a cost guide, you’d be 2 days of a machine (5T or 4CX) and operator so around the £750 for that. 4 loads of muck away, £1k round here on a grab wagon.

 

MOT 1 is £8/m² laid, so that’s another £1k. 

 

Adding in mesh, chairs and shuttering is probably 2 days for 2 guys assuming single layer and nothing clever so £1k labour and £1k of A252 and chairs etc

 

Concrete - you can’t just drop 21

cube of RC25 in and let it flow so you probably need a team of 3 for the day - it will need floating so it’s probably £800 labour plus float hire. You should be able to get the concrete at around £100/cube so £2200 would cover it.

 

All in, you’re at the £8k or so mark which isn’t too bad. 
 

You could trim this as tbh I think the mesh is overkill in this, and I’d use fibres instead but also thicken the edges of the slab to 400x400 so the portal frame is bolted to it. That would remove the mesh and add 3 cube of concrete. Add an extra day for digging out (£375) and fibres (£100) then it’s taking about £1200 off the pricing

 

What sort of pricing have you been given..? 

 

 

[Pabbles]

Connor/Peter - thank you both very much indeed for that - especially for the breakdown, that's just what I needed.

 

Peter - you're quite right 21m3 not 27m3. I had been debating between 200 and 250mm thick as the info from the lift manufacturer specifies 200 for up to 4.2T or 250mm for 5T or higher, I think I'd worked out 27m3 based off the (unnecessary) 5T loading.

 

The stage I'm at is:

 

1) decide between block built and steel for the building. Steel is coming in a bit cheaper (I think at the moment), with the cheapest supply-only quotes (ex.VAT) being between £17,250 (no insulation) and £21,785 (with walls and roof 40mm insulated) - excluding erection costs at circa £5k ex VAT. Done.

2) finalise/sharpen the best quotes and get drawings - in progress, pending rationalisation of all the quotes.

3) submit to Planning Authority for Lawful Development Certificate - not started

4) get the certificate and get formalised groundworks quotes - not started

5) pay for the building -not started

6) get groundworks done - not started

7) put up building - not started

 

So far, the only pricing I've had back for the slab/groundworks is from two sources:

• One of the steel building suppliers included it on their quote at £19,440 plus VAT (that's the one I thought was bonkers)
• I've just called one local (larger) groundworks company to get a rough guide and he said £13,800.

 

The insight from yourselves is invaluable as it already tells me that my gut was right and £19k+VAT is indeed nuts but that the quick quote from the local firm is probably at the upper end of what I might expect.

 

For info the building is 12mx9m with a 4m ridge and 2.5m eaves (keeping it under PD regs). The span is 12m rather than 9m (the only way to fit my vehicle lift into the roof space).

Edited January 13, 2023 by Pabbles

[PeterW]

2 minutes ago, Pabbles said:

3) submit to Planning Authority for Lawful Development Certificate - not started

how is it lawful ..? It’s very big to be under PD..!

 

And you need building regulations for that size so factor that in.

[Kelvin]

My 10.5mx6m is £6k for all the groundworks for a similar steel garage/workshop. The SE did a foundation design for us but that was part of the overall SE cost for the house etc. 

[Pabbles]

Peter: that's the bit I'm struggling with at the moment, we've spoken to two architects and two planning consultants and we can't get a straight answer but all have said its technically under PD but best to go for a Lawful Development Certificate to be safe.

 

Their reasoning is that:

 

1) its >2m away from any boundary (which under PD means the pitched roof can go to 4m)

2) even at that footprint it only takes up 7% of the available curtilage (its a massive garden, about half an acre and the boundaries near the building are all onto empty agricultural land)

3) The eves are at 2.5m from natural ground level

4) The ridge is at 4m or lower from natural ground level

5) its set back from the property

6) its not in any protected/greenbelt/conservation land and there are no restrictive covenants on the title.

 

I've anecdotally heard about a 30m2 limit to PD in some areas (not the 30m2 Building Regs limit, a separate one for footprint) but haven't been able to find anything in the local authorities policies.

 

That does seem to hit all the PD markers - bigger than they might expect, but that's due to the size of the garden. Unfortunately the PD Enquiries service is shut down at the local authority, so the only way to get some confirmation is an LDC otherwise its full planning, which I don't want to do due to the pressures that this particular planning authority (Cheshire East) are seeing at the moment - I suspect saying 'no' would be quicker for them to get it off the to-do list.

 

Fully recognise that Building Regs are a factor being >30m2, I should have mentioned that above - yes we're fully expecting that.

Edited January 13, 2023 by Pabbles

[Pabbles]

5 minutes ago, Kelvin said:

My 10.5mx6m is £6k for all the groundworks for a similar steel garage/workshop. The SE did a foundation design for us but that was part of the overall SE cost for the house etc. 

 

Thanks Kelvin - that's really helpful too.

 

10.5x5 is about 58% of 12x9 which would make an equivalent price about £10,300.

[joe90]

36 minutes ago, PeterW said:

how is it lawful ..? It’s very big to be under PD..!

Interesting because I am considering a garage under PD rules that’s bigger than 30 sq m but cannot find an answer. I would like to build closer than 2m from the neighbour so may go for planning (but with a caviat that if they refuse I will build it anyway under PD 2M from the neighbour 🤷‍♂️).

[Pabbles]

The 2m rule is only if you want the ridge height to be the full 4m. If you're happy with 2.5m of height then you can be closer to the boundary but as I understand it some local authorities seem to have different interpretations of the rules.

[Kelvin]

My ridge height is 4.2m with the eaves at 2.5.  The original planning permission was 5.1m for the ridge height for a timber kit garage but I ditched that due to cost. Block build was also slightly dearer. 

[joe90]

30 minutes ago, Pabbles said:

The 2m rule is only if you want the ridge height to be the full 4m. If you're happy with 2.5m of height then you can be closer to the boundary but as I understand it some local authorities seem to have different interpretations of the rules.

If it’s 2.5m height then only a flat roof will pass (which I do not want) anything over the 2.5m (if within 2 m of the boundary) requires planning, but as you say no hard and fast rules seem to appear on the website 🤷‍♂️

[nod]

1 hour ago, Pabbles said:

Connor/Peter - thank you both very much indeed for that - especially for the breakdown, that's just what I needed.

 

Peter - you're quite right 21m3 not 27m3. I had been debating between 200 and 250mm thick as the info from the lift manufacturer specifies 200 for up to 4.2T or 250mm for 5T or higher, I think I'd worked out 27m3 based off the (unnecessary) 5T loading.

 

The stage I'm at is:

 

1) decide between block built and steel for the building. Steel is coming in a bit cheaper (I think at the moment), with the cheapest supply-only quotes (ex.VAT) being between £17,250 (no insulation) and £21,785 (with walls and roof 40mm insulated) - excluding erection costs at circa £5k ex VAT. Done.

2) finalise/sharpen the best quotes and get drawings - in progress, pending rationalisation of all the quotes.

3) submit to Planning Authority for Lawful Development Certificate - not started

4) get the certificate and get formalised groundworks quotes - not started

5) pay for the building -not started

6) get groundworks done - not started

7) put up building - not started

 

So far, the only pricing I've had back for the slab/groundworks is from two sources:

• One of the steel building suppliers included it on their quote at £19,440 plus VAT (that's the one I thought was bonkers)
• I've just called one local (larger) groundworks company to get a rough guide and he said £13,800.

 

The insight from yourselves is invaluable as it already tells me that my gut was right and £19k+VAT is indeed nuts but that the quick quote from the local firm is probably at the upper end of what I might expect.

 

For info the building is 12mx9m with a 4m ridge and 2.5m eaves (keeping it under PD regs). The span is 12m rather than 9m (the only way to fit my vehicle lift into the roof space).If you can get it all done and graded around it for 13800 

Your doing ok 

Theres probably 4K in concrete 

Muck away is up to £300 per 20t wagon There’s  always more than you expect 

BR will be cheap and straightforward 

Pay a SE a few hundred for a design BC will just check that your following this 

A foundation design will help you get accurate quotes also 

 

[Pabbles]

thank you.

 

That's been really helpful everyone. Has already come in handy with challenging costs down with building suppliers (they folded immediately). Awaiting final drawings then off to formal quotation.