ICF and Foundation design

[Renegade105]

Hi guys,

 

in need of help!

 

due to clay ground conditions and nearby roots, been informed piled foundation will be more economical then strip (as they will be crazy deep and wide)

 

fair play, but now my ground beam engineer and my ground worker are very very worried at the huge Dead Loads and Live Loads on the external walls and ground worker is basically saying it is going to cost an absolute bomb to put 600wide cages for the ground beams.

 

we have a ground floor foot print of appx 250sqm, so daily big around 22x10 sqm 

 

I am going to reduce some of this loading by building an internal load bearing wall to take some of the load of the attic trusses, and thus reduce the load on external walls.

 

can anyone recommend a ground worker in Bucks area or around that won’t try to pull a fast one and is able to work to a reasonable price?

 

I was praying for less then £40k tbh, at this rate it’s going to be far more!

 

thanks,

 

 

[JohnMo]

I would be speaking to the structural engineer first, all respect to the ground workers but they are not qualified to make engineering design changes.

[Mr Punter]

+1 The pile and ground beam design need to be done by an engineer.

[Simon R]

Our ICF build is on clay and we looked at piled but ended up with and insulated raft. We had to get soil testing done but the structural engineer was happy with an mot base for the raft. A raft also has better thermal performance and is a good match for ICF.

[freshy]

On 27/08/2022 at 12:44, Renegade105 said:

 

 

due to clay ground conditions and nearby roots, been informed piled foundation will be more economical then strip (as they will be crazy deep and wide)

 

 

In a similar size ground floor & soil situation with clay, roots, etc.. I'm going for an insulated raft.

 

Which ICF are you planning to use?

[Renegade105]

Hi,

 

planning a Nudura build., 260m ground floor area, 600m total.

 

medium volume change potential CLAY.

 

ok guys, so quote for 41 piles to circa 19m are £28k

 

ground beams mix of 600x600 and 450x450 cages is a whopping £62k!!

 

None of this includes Drainage, Soak-away, Beam/block etc.

 

I was thinking if an insulated raft might help. I think I will still need piles due to the close

proximity of a tree 7m away and a 3m tall hedge which is 2.5m away.

 

thanks all!!

[JohnMo]

It's great getting all these prices, but where is the structural design.  If the structural engineer says no your back to square one.

[markc]

600x600 beams is in the realms of multi story car park simply supported main beams, let alone ground beams.

SE first, don’t build in problems and big overspends

[Mr Punter]

We have some 600w x 900d ground beams with a huge amount of reinforcing on 25m deep 300mm dia piles.  Total overkill but we were too far forward with the SE to change and the project was complicated.

[Renegade105]

Hi @Russell griffiths and @Mr Punter, any advice here?

 

essentially to get to DPC with Beam & Block we’re looking at least another £10k on top of the £62.

 

I have asked KORE and Tannards ( not my current SE) to finally let me know if an insulated raft is feasible or not, even paying SE charges again, if it saves me ££ then it’s worth it. I do have trees nearby so that’s the only thing that concerns me, and a hedge where the stumps are 1.5m away from the outside wall of my house…and I have to fit Inspection Chamber in between here.

 

my current SE reckons a raft is not feasible as might have to excavate 700mm of ground and then backfill with MOT, so that is a huge amount of muck away.

 

will keep you posted but anybody with experience with an insulated raft and associated costs then your help would be much appreciated.

 

 

[Gus Potter]

On 27/08/2022 at 12:44, Renegade105 said:

in need of help!

Hope this give you a few pointers and encourages further discussion on BH. Great to see folk posting about founds and so on as it's a big worry when you are trying to do a self build. Putting a price on the founds is like chasing cats.

 

On 27/08/2022 at 12:44, Renegade105 said:

we have a ground floor foot print of appx 250sqm, so daily big around 22x10 sqm

But how many stories is the house? and what is the construction?

 

21 hours ago, Renegade105 said:

ok guys, so quote for 41 piles to circa 19m are £28k

 

ground beams mix of 600x600 and 450x450 cages is a whopping £62k!!

The bit that I'm looking at first is your pile depth. I think there is something else going on here.

 

21 hours ago, Renegade105 said:

medium volume change potential CLAY.

Ok could be worse.

 

On 27/08/2022 at 12:44, Renegade105 said:

but now my ground beam engineer

 

Have you had a good site investigation done?

 

For all there are two kinds of generic site investigation report. The first is what we call a factual report. Here the Geotechnical Investigation company comes; maybe drills holes (could be a shell and auger rig, maybe window sampling, excavate trial pits, measure / monitor water levels, maybe some gas monotoring (if you are unlucky).. there are many "tests".  A key one is to determine what is in the soil.. is it contaminated, is it acidic or alkalie. Is it going to shrink and swell? What they then do is report the facts only.Thus a factual report.

 

The interpetive report means they (soil investigation company) take the findings of their tests and provide a more in depth report that tells you things like.. how much weight you can put on the soil and at what depth, how aggressive the ground is in terms of it attacking your concrete and the rebar in it. To get a good interpertive report the superstructure / piling  SE needs to be involved early so they can tell the investigation team what you are thinking of building and where you may want to put load. This is the most efficient way of doing this. Yes it will cost you more in professional fees on the outset but not that much when you consider the savings that could be made and most importantly justified.

 

But there is a difference in price here as if you provide an interpretive report as a site investigation company you carry much more liability, thus you need to charge more.. and often folk don't want to pay for that at an early stage.. they wait until their back is against the wall..

 

At some point the buck has to stop. I get factual goetechnical reports and have to interpret them. Thus I take on the liability and charge accordingly. If a Client has got an interpertive report then I can use these values directly and my fee goes down.

 

Again for all. It is really difficult to compare piling costs in particular. Roughly it's common to think of piles as a vertical column that transfers the weight of your building down to something solid. But from time to time the piles are subject to other loads. Say you have 10m of really soft clay on hard rock and a two storey house on top. Now often you'll find that if you install say a 150mm dia pile and just socket it into the rock (200mm say) you can put a lot of load down it. The socket is often required as the rock will have a bit of a weathered surface / a few fractures due to ice ageing. All good until you realise that you need to stop the house from blowing sideways on a windy day. The pile will just move sideways as it pivots at the bottom and the clay etc up the side just compresses.

 

To stop this happening you commonly make a series of flat portal frames (like B & Q roofs but just a but flatter). Here we make a stiff connection between the top of the pile and the ground beam. All of a sudden the ground beam is doing two things: acting as a beam to transfer the vertical loads to the piles and acting in conjunction with the piles to stop the building moving sideways. You can then see how the ground beam may need to increase in size. There is a balance to be struck here.. is it cheeper to make the ground beam much larger.. almost on first glance too large or do we increase the pile size and make the ground beam a bit smaller? Where lies the most economic design?

 

Last but not least if you have clay that can shrink and swell. When it shrinks it can still grip the pile so the piles has to carry not just the load from the building but a bit of the "hanging on clay" When the clay swells is can really grip the pile and tends to lift it up. Often swelling is not uniform and this too can push the pile sideways.

 

I hope the above give you a bit of insight into the "life of a pile"!

 

@Renegade105

 

Post the info you have and know about the site. The trees.. often this can be mitigated and if you are talking about 19m piles then I think (guessing) this is not critical to the design.

 

It may well be that the raft is an option but before you embark on this you need to know a lot about the soil, ground water flows, topography of the site etc. Also there are other options available, ground improvement and so on.

 

Post the info you have.. you'll get plenty suggestions here on BH, can be helpfull if even to rule things out.

 

 

 

 

 

 

 

 

 

 

 

[Gus Potter]

28 minutes ago, Renegade105 said:

will keep you posted but anybody with experience with an insulated raft and associated costs then your help would be much appreciated.

Happy to chip in with what I know. But I / BH folk need to know more about the ground before I / we could be of any real help on the nitty gritty.

 

Funnily once you get a handle on it an insulated raft is pretty simple to design. We have been designing insulated raftes for many decades in the commercial sector so it's nothing new.

 

With a good set of drawings you should be able to russle up a few quotes from contractors.. also approach the folk that do high end farm sheds.. they will also quote you. It's bread and butter stuff for them. Check them out on the farming forum, if they get the thumbs up from the farmers they have passed a test.

 

 

 

 

 

 

 

 

 

 

 

 

Edited September 7, 2022 by Gus Potter

[saveasteading]

2 hours ago, Gus Potter said:

to circa 19m

That is very deep, and suggests very thick peat or silt. What is the ground, and maybe you can get more soecific advice?

 

2 hours ago, Gus Potter said:

Client has got an interpretive report then I can use these values directly and my fee goes down

I wouldn't count on that. I'm pretty sure there is legal precedent for the investigation company taking no blame. 

I had a project where the client provided a comprehensive  report for tender, from a ground investigation company.  Tarmac on stone on clay supposedly. Contract won on that basis. As soon as we started digging we hit a reinforced concrete slab, which 6 boreholes had failed to identify.

We minimised the extra cost by redesigning,  but the client paid and the G I co and PM got away with it.

Either the supervisor was not paying attention x 6.. or they didn't do boreholes and guessed.

[Renegade105]

Update…. Went for insulated raft…the only PITA was the land drain as it follows the deepest part of the dig circa 1.1 m deep.

 

site is a tapered dig so we’re moving on full steam

 

Edited November 13, 2022 by Renegade105