Gavin’s isoquick foundation on clay soil

[gavztheouch]

About to start my isoquick foundation about 110m2. My soil is sticky clay, the top layer of clay about 1.5 meters is quite stiff then it turns to a watery jelly consistency. The plan is to keep the foundations shallow to bear down on the stiff clay. 
 

The isoquick should be arriving this week. I was hoping to get the slab finished before the end of October but the more I research the more work I find and details/levels to be found for the underground pipe work/ septic tank and rebar. It’s going to be a challenge I think. If I can get close to the end of October I’ll be happy, it would be helpful to not be pouring concrete in very cold weather.

[gavztheouch]

First job was building a road down the side of the farm sheds for access of heavy traffic. Tractor’s long term, concrete Lorries in the short term.

[gavztheouch]

 

Isoquick insulation arrived today.

[Duncan62]

Any reason you used isoquick over others? Interested as we're having a raft like this...

 

P.s. wish I had access to machinery like that, must make it easy!

Edited October 4, 2023 by Duncan62

[Declan52]

Did you dig any trail pits to see the depth of the jelly strata???

 

[gavztheouch]

  On 04/10/2023 at 20:24, Duncan62 said:

Any reason you used isoquick over others? Interested as we're having a raft like this...

 

P.s. wish I had access to machinery like that, must make it easy!

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No big reasons, the architect had used a few different companies and this was their preferred system. Personally I like the fact they had been around for a while and also the egg crate mechanism and dovetail joints on the blocks is pretty cool to lock all the insulation together.

 

Yes having machines and shed storage space is blessing and a privilege. 

 

  On 04/10/2023 at 20:47, Declan52 said:

Did you dig any trail pits to see the depth of the jelly strata???

 

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We dug a few trial pits. The engineer reckons there is at least 1m to 1.5m of stiff clay before it starts to get jelly like. For the foundations we need to strip back only the top soil which is about 150mm plus only 50mm of clay for a total depth of 200mm. Into this pit we fill back in 100mm of Type 3 with 50mm of angular gravel. This means the bed for the foundation is only 50mm below the existing ground level. The isoquick is 250mm of insulation and 250mm of concrete so 500mm in total meaning the top of the slab will be 450mm above the ground. The house is going to be sitting quite high in the field so Im going to have to blend the soil/garden heights with the rest of the field so it doesn't look weird. Good to be high out of the ground though.

[gavztheouch]

j

 

Edited October 15, 2023 by gavztheouch

[gavztheouch]

Click on picture for higher resolution,

 

Trying to work out my soli pipe runs, the architect has run them like shown in the pic, reduces the number of inspection chambers but means running a lot more pipe under the slab. For repairability in the future would it make sense to bring all the 110mm soil pipes straight out of the slab, it would mean more inspection chambers as there would be a lot more changes of direction. I especially don't like the run on the left side of the house that picks up the three soil pipes, one from upstairs, toilet and bathroom. What would you do?

 

Edited October 15, 2023 by gavztheouch

[saveasteading]

I agree. I think all foul drains should go a short route out of the house, but also square to the building as it makes construction easier.  A shorter run at a steeper grade is best.

ICs aren't very expensive as long as away from vehicle loading.

 

Where does the rainwater go? If it is to a big soakaway or pond on your land , then OK. 

Having a French drain all  around the house is OK if there is a problem,  but it should not drain your ground to mains or water courses,  which would be the opposite of flood mitigation.

[gavztheouch]

The French drain will go into the river forth. Because I’m close to the river I shouldn’t be causing any flooding Issues other than raising the height of the river forth itself. I don’t know if that’s an issue. Do people build houses without French drains? If so what are the alternatives. My dads house about 200-300 years old goes not have drainage like this. My 1930 flat does not have a French drain. It might have a gravel drain.

 

The 110mm soil pipes need a 90 bend to pop up through the slab. I assume I don’t need a slow bend here and a normal 90 rest bend will be ok here? A slow bend will increase the depth of the pipe a lot more. A rest bend needs about 300mm to go from horizontal to vertical. It needs to be vertical before going through the Iso quick slab.

Edited October 15, 2023 by gavztheouch

[saveasteading]

  On 15/10/2023 at 18:39, gavztheouch said:

French drain will go into the river forth

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Direct on your land?

All flooding is a combination of raindrops, so It all counts. Of course you could be at the trickle end of thd river or as it becomes an estuary, which woukd make a huge difference.

If your water could end up in someone's street or playing field, then its a bad thing to hurry it.  French drains and soakawsys are more often used to hold back water.

 

What is the reason for the French drain? 

This is a common solution as a retrofit to resolve a wetness problem. But in your case, if that iis x the worry, then it's probably better to raise the building.

I can't say more without knowing why this has been shown.

 

My current feeling is that it is a misunderstanding of drainage and attenuation.

 

 

[saveasteading]

Normal 90° bends are fine.

[jamieled]

I was under the impression that perimeter, french drains are a standard detail for all insulated raft type foundations, partly to reduce the risk that the angular gravel that the foundation sits on doesn't  become waterlogged.

[saveasteading]

Angular 'gravel 'doesn't get waterlogged, it just fills with water and I can't see how that is a problem. Wet stone.

If a properly graded stone  is used, that is then compacted, the amount of water would be tiny. Even an eps base won't float a concrete slab.

I remain to be convinced of the value of kit rafts anyway (other than easy diy), so would be interested to hear more on this subject.

[IanR]

  On 15/10/2023 at 21:25, jamieled said:

I was under the impression that perimeter, french drains are a standard detail for all insulated raft type foundations, partly to reduce the risk that the angular gravel that the foundation sits on doesn't  become waterlogged.

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The "no fines" pea shingle or granite chippings are there to be free draining and the French drain is to lower the water table so the bed the EPS is sitting on is kept dry. If the EPS is sitting in water (up to the DPM) then its been thermally bypassed. ie. if you have 3 layers of 100mm thick EPS and the DPM is between the bottom two, with the water table above the lower layer, then you've effectively only got 200mm EPS.

[saveasteading]

  On 16/10/2023 at 12:54, IanR said:

no fines" pea shingle or granite chippings are there to be free draining

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But if you put down a solid sub base, then no water flows through it.

Sounds to me like standard details to overcome problems that aren't necessary.

Perhaps assuming the worst combination of circumstances and applying excessive solutions regardless of necessity. 

 

Water table us not usually near the surface.

 

Use proper sub base, raise the building above ground level. Too simple?

[IanR]

  On 16/10/2023 at 14:58, saveasteading said:

But if you put down a solid sub base, then no water flows through it.

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If there's either water moving through seams in the clay, (after rain) or a high water table, which brings the water up to the EPS level, then water would move between the sub-base and the EPS and in between the EPS layers (below the DPM).

 

The EPS under the ring beams will likely be around 500mm - 600mm below FFL, and for the majority of the floor area around 400mm below FFL.

 

There are quite a few companies now Engineering these insulated rafts, and (at least when I looked) they were all using a similar build-up.

[saveasteading]

  On 16/10/2023 at 15:07, IanR said:

If there's water moving through seams in the clay,

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I don't think that happens. Try a soakaway test and notice how the water doesn't drain on clay.

 

  On 16/10/2023 at 15:07, IanR said:

or a high water table,

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Must be incredibly high. 

 

  On 16/10/2023 at 15:07, IanR said:

water would move between the sub-base and the EPS and in between the EPS layers (below the DPM).

 

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That seems to be the problem...of the system...so isn't there a dpm under and around the eps?

£100 Solution instead of £2,000 for single sized gravel with 1/3 air for water to flow through, and a land drain, dewatering the land (a bad thing).

 

Anyway, how does the water get under the footings and then up to the slab? Ahh yes, because of the loose gravel.

 

  On 16/10/2023 at 15:07, IanR said:

they were all using a similar build-up.

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I would put it differently. They are assuming lots of challenges occur on every site. They are not Civil Engineers and are being ultra cautious, spending their  clients' money.

And they are copy catting.

 

 

 

 

  On 16/10/2023 at 15:07, IanR said:

around 400mm below FFL.

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But that is how far below outside GL.? 200mm?  That's not a water table, it's a flood.

 

I'm not disparaging these systems. I 

can see that this utracautious design saves worry, and maybe problems,  with amateur builders and architects who don't do drainage.

 

Anybody setting out on this method has a choice though. Ask away.

[IanR]

  On 16/10/2023 at 17:37, saveasteading said:

I would put it differently. They are assuming lots of challenges occur on every site. They are not Civil Engineers and are being ultra cautious, spending their  clients' money.

And they are copy catting.

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I appreciate you do not understand this system. It's disappointing that your lack of experience with it would have you challenging the knowledge of the Structural Engineers designing the system, rather than considering your knowledge is incomplete.

 

  On 16/10/2023 at 17:37, saveasteading said:

I don't think that happens. Try a soakaway test and notice how the water doesn't drain on clay.

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It does. Seen it with my own eyes. Had I not been sure I would have caveated my response.

 

  On 16/10/2023 at 17:37, saveasteading said:

That seems to be the problem...of the system...so isn't there a dpm under and around the eps?

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No, that would put the DPM at risk.

 

  On 16/10/2023 at 17:37, saveasteading said:

But that is how far below outside GL.? 200mm?  That's not a water table, it's a flood.

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FFL would typically be 150mm above GL, so 350mm - 450mm

 

The water table at my old house was 100mm below the garden level, unless it had recently rained.

 

  On 16/10/2023 at 17:37, saveasteading said:

I'm not disparaging these systems. I 

can see that this utracautious design saves worry, and maybe problems,  with amateur builders and architects who don't do drainage.

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You are coming across as if you are. "Ultra-cautious" would be opting for a 250mm reinforced raft with loads of steel, and spending a client's money on unrequired concrete & steel and extra dig depth. If you take some time to look into insulated rafts you'll actually find that they are, in most cases, Engineered for the actual loads they take and the ground they are sitting on.

 

The one system that does follow more of a "one-size fits all" approach is the Isoquick system that is the subject of this thread, but it still out performs traditional foundations and is comparable in price (when apples are compared with apples).

[joe90]

  On 16/10/2023 at 17:37, saveasteading said:

That's not a water table, it's a flood.

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Well on my last build which was on solid yellow clay in winter the water table was only just under the ground level (50 - 100mm), not a flood but a consistent level.

 

  On 16/10/2023 at 18:01, IanR said:

  On 16/10/2023 at 17:37, saveasteading said:

I don't think that happens. Try a soakaway test and notice how the water doesn't drain on clay.

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It does. Seen it with my own eyes. Had I not been sure I would have caveated my response.

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I disagree, on solid clay water will not drain away unless on a slope. Although I used strip foundations we backfilled the trench outside with 50mm stone to create a French drain and I extended it to a nearby ditch which worked perfectly at keeping the water table lower.

Edited October 16, 2023 by joe90

[saveasteading]

I am reminded of a competitor. They were successful and their buildings were good. But their skills were more in marketing than construction.

They had several big technical issues over the years. Each time, they commissioned a process so that it could never happen again. One was crazy and a building collapsed. The others were very expensive ways of working, idiot proofing I suppose, for a single problem where the issue may never reoccur.

Their prices rose, and they fizzled away. Then people told me all this stuff.

 

They were designing a completely standard method of construction assuming that all their previous problems would reoccur on every project. The client paid.

 

It feels as if the procedures discussed above are similar. Solutions but to be applied regardless of the need. 

Mostly it will do no harm. Although dewatering to a stream is the opposite of sustainability.

[saveasteading]

  On 16/10/2023 at 18:29, joe90 said:

solid clay water will not drain away

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That's what i said , or implied.

 

  On 16/10/2023 at 18:29, joe90 said:

a nearby ditch which worked perfectly at keeping the water table lower.

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Clever enough if there was a problem to overcome, but aiding flooding downstream.  Should not be a standard process.

But why? As long as the water table is below the dpm, or kept out by a perimeter membrane, it does no harm.

[IanR]

  On 16/10/2023 at 18:29, joe90 said:

I disagree, on solid clay water will not drain away unless on a slope. Although I used strip foundations we backfilled the trench outside with 50mm stone to create a French drain and I extended it to a nearby ditch which worked perfectly.

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Is the trench with 50mm stone not capturing the ground water and taking it away to the nearby ditch? If it was only taking away the surface water then a surface drain would haven been sufficient.

 

If ground water doesn't move through clay then French drains would not work in clay (apart from removing surface water).

 

The biggest yield improvement we saw on our arable farm, which is/was on Essex clay, was when we started mole draining in the late eighties. That wouldn't work either, if ground water didn't move through clay.

Edited October 16, 2023 by IanR

[saveasteading]

  On 16/10/2023 at 18:01, IanR said:

and is comparable in price

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I'd have to see details, but it seems very unlikely to me.  NB me building it   ( 300 + projects) is not the same as self build. I am challenging the assumptions for the potential benefit of the poster who can be persuaded by me or not.  It's his money that is being spent.

 

You are right that I don't know the system. But I have been optimising construction for decades.

Onmone project i designed and costed 6 methods of construction.( Eps block being one.) 

 

So I do want to know if I'm wrong. By challenging I clearly get a response.

 

I'd love someone to explain why a traditional graded sub base and dpm are not better in performance and cost.

 

 

 

"out performs traditional foundations.

Says the manufacturer?

In strength? Cost? 

 

If I'm coming over too heavy then I apologise.

 

[IanR]

  On 16/10/2023 at 19:04, saveasteading said:

I'd have to see details, but it seems very unlikely to me. 

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And if you are coming to that conclusion without costing both on the same job, then that's quite possibly confirmation bias.

 

For you, maybe traditional founds would be more cost effective, maybe you have a network in place that helps deliver that cost effectively.  Without a network in place, I costed both options for bringing in the required trades and materials.

If you think about it though, like for like, an insulated raft is going to be cost effective, unless someone's adding on a big margin. There's less dig, less concrete (and or no block and beam), maybe more steel, but nothing exotic, cheaper insulation (EPS in lieu of PIR/PUR) and no screed. But, you do need to pay an SE to Engineer the foundation system.

 

  On 16/10/2023 at 19:04, saveasteading said:

"out performs traditional foundations.

Says the manufacturer?

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Yep, all the manufacturers do of course say their product is better performing, but I'm talking about calculating the thermal performance for PHPP. There's a lot to do to a traditional foundation to get it close to being thermal bridge free, but for an insulated raft it's inherent in the design. ie. the exterior walls are sitting on the raft, which is insulated from the ground.

 

While insulated rafts remain niche in the UK, they are more-or-less standard in Sweden. It's a well proven technology.