Not allowed EPS under slab!

[Chablais]

So I have had a ten ton digger pecking rock out to make way for a basement and extension. Was planning on 200mm EPS under the slab, and 200mm EPS around the exterior of the basement walls. I do have two walls against the existing house to retain the house founds, as well as creating the basement walls. SE has categorically stated he will not entertain EPS300 under the slab. We are on solid rock for almost the whole slab. It is supporting three stories above. Some pics showing existing founds etc. Was going to use Jackodur system as it also creates the former to pour the concrete too. 

I was initially concerned when we exposed the existing house founds and the SE had a fit and demanded all work stop, until the house was underpinned. However I elected to continue and pecker out the rock, wether through luck or judgement the house is still standing.

So now I either accept the SE proposals or find another one for a second opinion.

 

Rebar sched2 (1).pdf

SE version2.pdf

Edited August 15, 2018 by Chablais
spelling

[Nickfromwales]

Hi and welcome. 

If not EPS then what was the suggested alternative?

 

[Jeremy Harris]

What reason has he given for not accepting EPS under a slab?

 

It's very widely used in the UK, and all over Europe, so there has to be a specific concern he has that relates to your particular set of circumstances.

 

It can't be waterlogging, as EPS has been used for decades in waterlogged foundation conditions.  Perhaps it's to do with load spreading through the underlying blinding?

 

Until he says exactly what his specific concern is it's hard to try and come up with an alternative suggestion.

[Russell griffiths]

The problem with finding another will be the time delay

unless you have already got one in mind

mine is booked for a month in advance at the moment 

it could be easier to do it how he wants and you can get your concrete in next week

 

mine has just suggested something I didn’t like and I was going to argue my point, but in the end it seemed like I could spend half a day arguing or a couple of hours work and do it how he wanted and move on to the next stage. 

[Chablais]

Hi All

His major concern is giving support to the existing foundations, he has said that he thinks the EPS will deform under loading. He also said he thinks the whole raft could slip.

I said i thought the reinforced slab would spread the load, and had suggested using EPS300. There appears to be plenty of steelwork both in the slab, which has A393 and A252 mesh, and the walls which have 12 and 16mm rebar and A393 mesh. My concern is that he may be saying this as he may not have any experience of using EPS. He is even against me using it on the exterior of the basement walls.

He is suggesting a 50mm concrete blinding to level the site and 200mm concrete on top. As it stands I will need much more material to level the site, circa 150-200mm in places.

Double whammy on finding another SE, as all very busy with at least a month wait, plus the extra costs of paying two. 

As a layman it seems at odds to argue with the proffessionals, but I was hoping to be much more thermally efficient with slab on EPS method

Not sure which way forward, architect has sided with the SE as expected.

[Triassic]

I’d suggest he doesn’t really understand how EPS raft foundations work.

 

Ive just built a basement on limestone rock. The basement sits on 200mm of EPS. There is 26m3 of concrete in the raft and 26m3 of concrete in the retaining walls, there’s also about 4 tonnes of steel  reinforcing in the whole lot. I have 170mm of insulation behind the retaining walls. The house sits on top of this lot!

 

Edited August 15, 2018 by Triassic

[Jeremy Harris]

Definitely has no understanding at all of how a raft on EPS foundation works.  Might be an idea to let the SE have a copy of this Kore report:  http://www.mayfly.eu/wp-content/uploads/2017/12/Kore-Insulated-Foundations-Report.pdf

[Russell griffiths]

As far as I understand if he is worried about slipping, you can include a trench in the center that acts like a key way 

why use concrete to level? 

Can you not use crushed stone compacted and eps on top. 

[Chablais]

Thanks all

Going to try again tomorrow and furnish JSHarris report, thanks. It seems like trying to push a river upstream, everybody in the construction trades I have spoken with regarding the build shakes their heads when I mention insulation, airtightness or U values. Done it this way for 30yrs and it will be good enough for you! Except it isn't,  and it will be me doing any extra detailing and labour, not them.

 

[Chablais]

Hi Russell

 

We are effectively in a hole, hacked out of solid rock, I find it unlikely that it would move. I also thought crushed stone was the answer to levelling the substrate. Will have to see what headway I can make tomorrow. Will also phone around some SE and see if anyone would take it on just this element as a one off.

Thanks again for the positive support.

I thought I had a bad day when we hit rock on the first day of digging!

I guess it will get a lot worse before it gets better.

 

[Jeremy Harris]

7 minutes ago, Chablais said:

Thanks all

Going to try again tomorrow and furnish JSHarris report, thanks. It seems like trying to push a river upstream, everybody in the construction trades I have spoken with regarding the build shakes their heads when I mention insulation, airtightness or U values. Done it this way for 30yrs and it will be good enough for you! Except it isn't,  and it will be me doing any extra detailing and labour, not them.

 

 

 

You are far from being alone!

 

We encountered much the same, from architects to builders, and found it extremely frustrating.  It seems that there is a general reluctance in the domestic sector of the building industry to change from doing things the way they've done them for decades, even if what they've been doing for decades is building crap!

[Triassic]

18 hours ago, Chablais said:

Will also phone around some SE and see if anyone would take it on just this element as a one off.

There is only one guy I’d recommend, his name is on the report Jeremy linked to. He did my foundation. He really knows his stuff, he’s designing insulated raft foundations every day.

Edited August 16, 2018 by Triassic

[Russell griffiths]

Instead of looking for a SE that understands what you want to do. 

Why not ask an insulated slab supplier to recomend one. 

 

I am building in ICF and am using the SE recommended by the block company, he also specialises in passive slabs. 

But he’s over a month away from doing mine, and I booked him in 6 weeks ago. 

[Alexphd1]

Your not alone, been there got the t-shirt aswell? 

100% with triassic he also sorted as out.

 

[Triassic]

You only get one chance to get this right.

 

I talked to a number of SEs locally, none of them really understood insulated foundations like Hilliard Tanner, he is the go to guy. I, like you, went with a local SE who came recommended, he like your guy, wanted to lay over site concrete on top of rock, what a waste of time! And do traditional strip foundations.

 

Realising I’d made a mistake so I went with someone who knows what he’s doing. In the end I also laid all the insulation, installed the rebar and worked with a local concrete pump guy to lay the concrete. All very satisfying and I saved money as well. One company quoted £150k for a job that cost me around £50k on a DIY basis.

 

@Chablais  I've just realised your in Cumbria, come and visit the my site, in based in Witherslack and you can take a look at my basement and a partially complete insulated raft foundation, concrete pour next week!. Message me if your interested.

 

 

Edited August 15, 2018 by Triassic

[Chablais]

Hi Triassic

 

Thanks for the info. I have  emailed Hilliard Tanner and will try calling tomorrow. I really cannot understand not wanting to insulate the foundation and basement. Did you use Ian PArker for the concrete pump?

Are you waterproofing the inside or outside of your basement

Hope I can make some progress, as you correct, only one chance. I was hoping to have a roof on by the time the clocks change!

Thanks

 

[Triassic]

I am using Ian, he’s a good hard working guy.

 

I have used ICF to construct the basement walls. Waterproofing is on the outside and is protected by a 100mm thick layer of polystyrene to stop the backfill damaging it.

 

 

Again, come and have a look.

Edited August 15, 2018 by Triassic

[Pocster]

My ‘hole’ carved out of solid rock 

Eps in the centre of the ‘raft’ ; styrofoam flooring ( kpa 500 I think ) under the edges of the ring beam .

no problems ?