Raft foundation drawing query

[Paul84]

Hi everyone, I seen this forum when searching about raft foundations. Who knew how expensive they would be, I've been quoted £9k and £7.5k so far so I've looked at doing some myself and splitting it down to individual jobs, e.g pay a guy to dig it out, get someone in to show me how to build the metal work, get someone in to do the concrete. 

Obviously all checked at stages by building control. 

What are your thoughts on this people? Raft is 8.5m x 4m. 600 wide edging down to 1.2m, slab is 200. 

It's for a single storey extension on my house.

Or if anyone is based in North East England give me a shout. 

[Mr Punter]

If you have not done this before it will be much less painful just to get a price.  £7,500 works out at £220 per metre.  Is that price all inclusive labour, materials and muckaway?

[Paul84]

Hi Mr. Punter.

Yes that's all inclusive price. 

I've not done this before no, I just wasn't expecting these prices. Got another quote coming this weekend. 

 

[Bitpipe]

Most here who have used a raft have done it as an insulated raft, with high strength EPS under the concrete and UFH embedded directly in the slab so no need for insulation or screed on top.

 

This looks like an extension though so maybe not appropriate.

[Paul84]

Hi Bitpipe. Yes it's for an extension. I plan on putting UFH in but the images are what my SE has done and I'm not wanting to change it now really. Unless others can really recommend what your saying.

[PeterW]

You can’t use that design for UFH - there is no insulation under the slab and it also seems to show an additional layer on top. How low has the SEng drawn the top of the concrete in relation to the finished floor of the existing house ..?

 

And why a raft for such a small extension ..? What are the ground conditions ..??

[Mr Punter]

It may be good to dig a pit and expose the existing foundation.  Unless you have experienced subsidence the single storey extension foundations could be made the same. 

[Paul84]

Hi Peter, thanks for your comprehensive reply. I didn't know about that for UFH.. 

Top of concrete to current finished floor is approx 200mm. 

 

I said the same to the SE but my neighbor has conifers 1.5m to one small section. Crazy but he said I have to do a raft. 

Ground is my back garden, currently lawn. 

[Paul84]

Hi Mr. Punter. 

SE said I had to use raft.

[Paul84]

Question; what are the dimensions of the Z bars, any recommendations for companies to supply steelwork. 

 

 

[Russell griffiths]

Your dimensions of steel will be in the BAR BENDING SCHEDULE  this is produced by the engineer, you send it to the steel stockholders and they produce a quote for you. 

£7-9 grand I would just pay it, the time you pay for all the separate elements you will be lucky to save £1500 for weeks of agro. 

 

Foundations is not a place for you for you to try and make savings. 

Fitting plasterboard, door linings doors, skirting and painting are the things you can do unless you have done it before. 

 

now im all for everyone having a go, I did all my own steel work and ringbeam and saved £5000 but I’ve been involved in the building game for nearly 40 years. 

 

What about drainage, do you have drainage going under the raft?  

[Venkat]

Hi Guys, I also need a help in finding a contractor for my raft foundation, I got the design from my structural engineer, m looking for a contractor , if you guys know please help. I am living in Slough, mine is 6.8 X 3.5 metre single storey extension.

Attached raft design

520 - Dashwood Close-A3.pdf

[Paul84]

Hi Russell,

Thanks for the reply. 

I definitely have 1 drain which will need checked for route but until we get down there I don't know. 

When the building inspector signs each stage off surely it doesn't matter what it cost it's done to the same standard otherwise it wouldn't be passed. 

 

 

[Venkat]

Sorry Russel to post my comment this thread, I found your message matching my requirement :), Hope it is ok

[Venkat]

I mean Paul84

[Paul84]

Hi Venkat.

I used mybuilder website before coming on here and suggest that's a good place to start. 

[Venkat]

Thanks Paul, will check

[Paul84]

Can someone check for me the previously posted NHBC depth calculation. I've got the type as a moderate water demand and they don't go deeper than 2.5m even if 1m from foundation. 

I'll look again tomorrow and measure the distance again to see if I do need this raft. 

Other second views appreciated. 

[Makeitstop]

If you can tolerate it, I'd pay it, as was suggested above. Savings can be made elsewhere.

 

As a comparison, I'm trying to organise an extension, but have to have piled foundations. On a structure of approx 6.5 x 3.5 metres, it's looking like £8400 just for six piles, with the ringbeam extra, so your raft doesn't seem quite so bad from where I'm sat.

Edited March 20, 2021 by Makeitstop