Workshop floor

[Mole]

Just had prices in for new workshop floor.. I was hoping for around £3k.. dimensions are 6.2*12.2m going to put one course of engineering bricks then wooden structure on top.

Will use for storage and working on Westy plus storage of ride on mower plus general workshop.

Going on good dry ground..

Quote from local decent builder £5900 plus vat including £900 for insulation under Vs £3450 from another guy with out insulation.

Builder including £550 worth of steel reinforcement other only quoting fibre reinforced.

Does the slab need mesh for the intended use?  Have worked on 150 mm of concrete more round edge, plus 100mm of hardcore.

Do the prices seem to be ok? One high one low? Which spec?

Thanks

[Mark (smokey mow)]

What's the subsoil? 

Are there any trees within 20m?

Is site access resonable?

Do the quotes include muck away?

What reinforcement are they proposing A142, A253 or A393? And in how many layers?

 

A building of 75m2 will also need building regulations approval and I'm afraid to say that neither of those specifications will currently comply with that.

 

 

[Mole]

Thanks Mark

Good access no trees subsoil not sandy or clay.. 

Muck away included on high price on other includes spreading on field..

Cheap cost just fibres added don't have details of steel in the other but the builder was confident it would easily meet regs with the steel he has allowed for

 

Yes I have been in contact with building control ... But am getting costs together so I can weigh up what size to go for..

A friend just did 60 M2 including a lot of muck away no reinforcing and no building control for 3k... 

So trying to understand the pricing..

So I guess you will suggest getting in touch with BC and agree spec...

[Oliver1]

My approach would be employ a Structural Engineer to do a very quick design. Will not be expensive and can be used to acheive Building Regulation approval. You can then get appples for apples prices.

Better value could be achieved from splitting the works down ie excavation (driver and excavator), concrete and brickwork.

 

[Mark (smokey mow)]

1 hour ago, Mole said:

Thanks Mark

Good access no trees subsoil not sandy or clay.. 

What is it if it's not sand or clay? 

Unfortunately you cannot even begin to correctly design a foundation or the reinforcement within it until you know how cohesive the subsoil is and what it's ground bearing capacity is.

[Mole]

I guess I was seeing it as a slab for putting a light weight building on it.. and appreciate the size..if it was under 30m2 then under building regs and realistically a simple proposition.. there are enough slabs around here which are put down with hardcore and then the slab..

I will take further advice and as you said Oliver get a structural Beng to draw up... It is looking more complicated than the foundations for a similar size extension to my house! Thanks both of you.

[Mark (smokey mow)]

Taking further advice from an engineer would be very wise. 

Its not so much the weight of the building that would be a factor in determining the adequacy of the foundation but the soil type and the potential of ground movement , the forces from which would far exceed that of the imposed load of the building on it.

Subsoils in east anglia would typically be either sands, clay, chalk or a mixture there off. Pure sands and chalk are non-cohesive and do not change volume seasonally or with moisture.  However clay will both shrink and heave seasonally. Certain areas of norfolk particularly around thetford are suspetable to sink holes due to the underlying chalk being eroded by water in the ground which causes the surface of the ground to collapse into the void left by the eroded chalk.  

On a building of the size you're building if the foundation slab is cast onto anything other than a sandy subsoils there is potential for differential movement where the subsoils on one side may move more than the soil over the opposite side of the building. If the design of the slab and the reinforcement within it hasn't given consideration to this pontenial movement then the slab will crack and fail, as the groud pressure tries to bend it. With a timber building this isn't so much of an issue as the structure is flexible and would be more able to accomodate failure of its foundations unlike masonry which is inflexible and where a foundation failure would also be transferred to the sturture of the building.

[Mole]

Thanks Mark.. Shame you aren't local..sounds like you could have helped me out!

Thanks again

[Steve (sdh2903)]

I went through the process about 3 years ago. Although for only around 25 sq/m but not straightforward as joined to the house and a build over a sewer.

I got in contact with the local building control early and they were a great help but the spec was ultimately decided by the water board who were a nightmare. 

Anyway I digress. I had half a dozen quotes and the price differences was almost as though they were quoting  for totally different jobs. Anywhere from 2k up to 8.5k for the exact same spec. So id keep getting more quotes.

Did your mate who did the 60m slab do it himself as that seems very cheap for a slab that size? 

[Mole]

Thanks Steve.. my mate got some one in..and the 3k included 60 tonnes of muck away.. he is going to price for me too...

For a slab with hardcore under materials are around 2k so it's doable for 3k...

[pistonbroke]

I would have thought 150mm of concrete on 100mm hardcore would be more than enough for a westy and a ride on mower .

My home build garage was completely DIY (except for the concrete base mix ) the build was single breeze block with 2 supporting colums on the concrete base , thickend at the edges . The substrata is clay and this area riddled with old mining works from the lancashire coal field . I had the plans drawn up and got these approved by local planing depot .  It took me 2 years to complete , that was over 50  years ago , its still there and in use daily , tere has been some slight settlement over the years but has not needed any remedial repair apart from the roof being replaced about 10 yrs ago .

[Mole]

That's what I was hoping.. now in process of drawing up plan and then discussing with building control...

Fingers crossed..