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(is this an ICF question or a foundation question ? both really ?

 

Ok, so 2 options under consideration 

 

1 - Insulated slab , KORE or Jackon or similar. Then off we go with ICF ... 

 

2 - Standard trench with insulated slab prob with UFH in the slab, ICF coming off the concrete strip. (as per Nudura drawing)

 

option 2 is simpler and therefore cheaper. Will I get a cold bridge issue ? Are the benefits of using insulated slab worth the extra cost ? other things to consider ? 

 

SE is steering towards 2 to save me costs, but am I compromising heat and insulation areas too much

 

 

 

B6A02_1.pdf

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What's not shown is the DPM, DPC, this needs to be shown.  I would be tempted to have a 50mm service void then plasterboard and dry line.

 

Overall there doesn't appear to be much insulation in the wall or the floor.  If you are going UFH heating your floor really needs a u value of 0.1 or better, in my option, otherwise a lot of the heat will travel downwards.

 

Not really seeing a thermal bridge with option 2, as you have continuity of insulation from the internal wall and around the underfloor areas.

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Yes missing DPM etc there. Also on the outer there’s a membrane but would that go below ground ? (Backfill) to the top of the trench. 
 

I know this bit is basics but I’m trying to gauge the cost/ value of the insulated system vs standard. Surely if the slab had enough EPS below and butts into the internal ICF the heat has nowhere to run away ?

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You are looking for continuity of insulation, which what I am seeing.

 

A lot also depends on who you get to do the work, we had no other choice than strip foundations and a structural slab, which was then insulated and further slab of concrete on top.

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Our house is long and not very deep, so the worst case for good u values, we achieved a floor u value  of 0.09 (200mm of PIR).  Had to do a lot of detailing on the sub walls below dpc, with thermolite blocks an loads of insulation, to get rid of thermal bridging, the structural engineer and architect introduced.

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4 hours ago, IanMcP said:

(is this an ICF question or a foundation question ? both really ?

 

Ok, so 2 options under consideration 

 

1 - Insulated slab , KORE or Jackon or similar. Then off we go with ICF ... 

 

2 - Standard trench with insulated slab prob with UFH in the slab, ICF coming off the concrete strip. (as per Nudura drawing)

 

option 2 is simpler and therefore cheaper. Will I get a cold bridge issue ? Are the benefits of using insulated slab worth the extra cost ? other things to consider ? 

 

SE is steering towards 2 to save me costs, but am I compromising heat and insulation areas too much

 

 

 

B6A02_1.pdf 64.66 kB · 12 downloads

How much do you expect to save? 

 

If you go for an insulated slab your main costs are 

Groundworks

Insulation 

Rebar

Concrete 

Labour 

 

A lot depends on your ground conditions, but you are going to need a digger, likely a dumper and either a whacker plate or a roller regardless. So if you plan to have a comparable amount of insulation where will the savings come from? Rebar? Labour? Not saying there is none, just wondering. 

 

The only reason I commented is I expect a quote from the groundworker for the 63m2 Insulated slab. 

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1 minute ago, oldkettle said:

How much do you expect to save? 

 

If you go for an insulated slab your main costs are 

Groundworks

Insulation 

Rebar

Concrete 

Labour 

 

A lot depends on your ground conditions, but you are going to need a digger, likely a dumper and either a whacker plate or a roller regardless. So if you plan to have a comparable amount of insulation where will the savings come from? Rebar? Labour? Not saying there is none, just wondering. 

 

The only reason I commented is I expect a quote from the groundworker for the 63m2 Insulated slab. 

 

kind of what I'm asking ... there's a savings question and a thermal target. 

Until reports prove different ground is ok for a strip foundation. 

 

Opt 2 - much simpler. dig a trench and concrete. that takes the wall load. less steel. (££) lay the ground slab , no steel. (££) Much less plant etc also. (££)

Opt 1 - lots more work to do to get ground prepped. More plant. More steel. Plus costs of system. 

 

Labour is me and what I can get away with plus skills if I'm failing. 

 

Opt 2 should hit thermal target, but will Opt 1 miss it !? 

 

Jackon provide a nice solution for slab and walls. looks lovely but costs. 

Want to put the £ where it's most effective. 

Doing it myself makes quoting that much harder as 1- new to me. 2 - don't know what I don't know ! :) 

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I am pretty much in the same position. Mine is on a slope and the groundworker admitted there is no problem losing the spoil in the garden. So in theory digging it is not a problem (I hired a digger once already), I am getting comfortable with a green laser level and surely driving a dumper is not scary, but - I don't know what I am doing ? so will likely pay somebody. Had a quote around 12K last year but this was before I had full SE drawings. And everything is way more expensive now, 20%+. Insulation is around 3.5K inc. VAT if I shop around. MOT3 is probably 600, filling clean stone is less, rebar seems to be maybe 2K including starter bars but I didn't search properly yet. 

 

Yes, sounds like you can save quite a bit - but please don't trust my word on this. 

Edited by oldkettle
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Pound for pound an uninsulated slab/raft and a high performance wall will give you more benefit than an insulated raft and high performing walls.

 

A correct sap assessment using supplier details rather than standard shows u values of walls isn't the be all and end all and a normal raft can be protected to afford some of the insulated raft benefits.

 

Based on experience from 40+ units of various designs.

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I have a major issue with icf onto an insulated slab, having built a house on a raft foundation we included a step at the edge, but seeing first hand how these are being built at the moment I really do not like the method of the flat slab with the icf sitting directly on the slab. 

There is a direct route for moisture to pass into the building at floor level. 

 

image.thumb.jpg.bc58151f5964fb1edd6fcc3310a9f2cc.jpg

see rough sketch. 

@IanMcP you need to be a bit careful using Nudura standard details, as it’s all a bit Canadian and needs adapting to suit your site. 

Edited by Russell griffiths
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@Russell griffiths

 

thanks , I'm leaning heavily towards standard strip foundation (and load bearing internals), some frost insulation on the outer side (could be overkill but cheap considering) , ICF & waterproof concrete coming from the top to above ground level, then ICF away we go... insulated ground bearing slab with UFH butting up to the ICF above what would be damp level. 

 

Could be any ICF in that config. front runners are Nudura and Polarwall (Alan is great!)

 

oh and that drawing looks angry !! ?

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41 minutes ago, Russell griffiths said:

There is a direct route for moisture to pass into the building at floor level. 

 

 

Do Nudura specify a swellable water bar at the junction?

 

I was told this was essential

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39 minutes ago, willbish said:

Do Nudura specify a swellable water bar at the junction?

 

I was told this was essential

Not essential.  Depends on warranty provider, architect, design etc.  Tend to stay away from to the waterbars that swell.  You need a dry day to install and then want keeping dry until covered with concrete.  Sika do a physical stop.  More practicable.

 

Get your outside done right and nothing else should be tested.

 

Waterproof concrete is a waste of money.  Something outside and something maintainable inside gives lowest cost option and satisfies most conditions.

 

 

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4 hours ago, willbish said:

Do Nudura specify a swellable water bar at the junction?

 

I was told this was essential

As above, warranty provider is key. Ours (Nudura) on a concrete slab with raised section under walls to help restrict water ingress and also helps keep water bar above any standing water. Just keep scaffold boards or something else in top of walls and maybe a few drainage holes if you think needed at wall base and don't forget to fill later ?. Also used waterproof concrete all from BASF. Seems to work so far ? 

I don't think Sika will warranty for ICF any more.

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45 minutes ago, Adam2 said:

As above, warranty provider is key. Ours (Nudura) on a concrete slab with raised section under walls to help restrict water ingress and also helps keep water bar above any standing water. Just keep scaffold boards or something else in top of walls and maybe a few drainage holes if you think needed at wall base and don't forget to fill later ?. Also used waterproof concrete all from BASF. Seems to work so far ? 

I don't think Sika will warranty for ICF any more.

I heard about sika......it's site and setting specific and, reading between the lines, depends on the ICF being used and who is installing it.  Sika, like others seem to like selling you every in the catalogue!  No brand bentonite works well but needs total protection until filled.

 

Physical step and properly pokered concrete is all you really need most mass poured ICFs everything else is just a failsafe

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We recently done trenchfill, then a course of ICF to GFL. 1st course filled with waterproof concrete as our DPC. Others are correct in that Sika won't warranty their admix in ICF method. I spoke to them directly and that's what they said. However, they also said that's not to mean it won't work. The only reason they won't warranty it was because they can't check it hence eluding not to the ICF itself per se but the quality control of the installation which they can't check like normal formwork which is removed and can expose any honeycombing. So we paid particular attention to ensure the mix was delivered per the spec along with careful pokering. That still leaves the detail at the top of foundation/bottom of ICF as @Russell griffiths mentions to deal with - in our case we've used an external waterproofing membrane up to ground level on the ICF and lapped over the top of the trenchfill to take any groundwater away from that junction into the land drain. Overkill possibly but for £500 of materials I'll rest a little easier.

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Really with just 1 course of ICF below ground you have some options to ensure all is ok with no dramas and I expect with no warranty issues. All compared to those with a basement or 2 that have bigger risk. 

You'll be fine ?

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Sika and others found out that for some icfs, the self builder is getting a warranty by the back door and then, when anything goes wrong, the warranty provider goes looking for someone to blame.

 

For example, one product essentially lets you be a qualified installer after two pours.  That's gf and FF.  Get your product sign off, sign your own warranty, still not knowing top from bottom. And then expect the warranty provider to play ball.  It's all good until it goes wrong.  Similar to the responsibilities under the h&s for all those labour only self build jobs.  Great until something goes wrong.

A peruse of the HSE website and legal gazetteers shows this to be the case.

 

Sika just got fed up with it and required extra back up.  Fair enough if you're going to get sued all the time.

 

Building control, engineer and the local environment will determine footing depth and rising wall height.  

 

@Tosh you get your cube samples assessed?  Pretty sure that's the only way to confirm specification.  Another reason why sika et al have restricted warranties.

 

 

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We have a 200mm waterproof concrete raft with a waterbar where the ICF is. The first pour into the ICF was also waterproof concrete. 

 

As with many ICF's it was almost impossible to poker the concrete inside the ICF so we used hammer drills on a thick ply board 6 inch square and vibrated the sides of the ICF. Worked superbly as you could see the concrete dropping when looking from above.

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1 hour ago, FM2015 said:

you get your cube samples assessed?

yes we're fortunate that we're really close to the quarry and I used to work there as well so know the lab staff. They pulled some samples from the batching and tested them for me which was all good. We were using a 200mm core ICF and, along with the right mix e.g. 10mm agg etc, could get good flow around all the nooks and crannies. Its been interesting as we've had to cut back the EPS to do some fixings that the SE insisted had to go direct onto the concrete and we've not seen any honeycombing anywhere.

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2 hours ago, Tosh said:

yes we're fortunate that we're really close to the quarry and I used to work there as well so know the lab staff. They pulled some samples from the batching and tested them for me which was all good. We were using a 200mm core ICF and, along with the right mix e.g. 10mm agg etc, could get good flow around all the nooks and crannies. Its been interesting as we've had to cut back the EPS to do some fixings that the SE insisted had to go direct onto the concrete and we've not seen any honeycombing anywhere.

The paradox is always the 200mm of pokered 10mm c35 is waterproof!  Just an excuse to relieve people of money!

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46 minutes ago, FM2015 said:

Just an excuse to relieve people of money!

yes there's been plenty of those..............unfortunately some have been successful! ? Hindsight a wonderful thing.

 

I pondered whether to use it, in the end had to come up with something to appease the BCO. Uplift of a couple hundred quid to the 1st load of concrete achieved that so seemed a good idea rather than some other solution for DPC. I did contemplate just black jacking the top of the 1st course but that would mean changing the approach i.e. 2 x visits to 1st FL rather than 1 x visit. Pump/labour etc which would have gone close to extra £1k.

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