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Insulated raft - ICF suppliers warnings ?!?!


BotusBuild

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My build method choice is ICF walls on an insulated raft foundation (ground conditions permitting). Talking with a supplier of a well known ICF product I have been warned that insulated rafts are susceptible to damage from vermin and oil. This particular supplier is the only one who has mentioned this.

 

This curve-ball has managed to (i) make me question the competence of this supplier as I have never come across this problem in the two year period I have been researching (ii) make me question whether this particular ICF system, by association, is any good (iii) query whether I should just go with strip foundations?

 

Anyone else heard of the "vermin/oil" problem? Anyone seen evidence of this?

 

The other comment from the same supplier was "for a basement there is no point in using insulated foundation because the ground below 1m is a constant temperature". I know that last part of that is factually correct, but I see others on BH using insulated raft for basements, so what are others opinions?

 

 

Edited by BotusBuild
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All ICF, if based on either eps or xps will susceptible to both rodents and any solvent based products. 

Get an eps icf block and chuck some acetone on it, it will melt away in front of your eyes. 

I don’t suppose that your suppliers thought to mention this as I thought it would be common knowledge. 

 

Its a bit like saying will my timberframe burn, yes it’s made of wood. 

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I think op is asking in the real world what's likelihood of these systems failing?

 

Could some contaminated ground or a spillage cause damage to the eps?

 

Is rodent damage a genuine concern once the building is finished? Can rats burrow? Are they likely to burrow and chew through eps?

 

All valid questions id have thought I'll leave it to others with the system to answer as I don't know

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Yes I’ve come across this twice 

The second was a build of three detached houses and you could see Rats coming out of the stream and burrowing in 

  

As Mike pointed out a render coat is needed 

Preferably with a steel mesh laid in 

I will try and route some pictures out that I took 

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Yes, their is a requirement to install a rodent barrier around the periphery of an insulated raft.  AFAIK, this has always been a standard requirement.  We installed a layer of heavy duty galvanised steel expanded steel mesh around the outside of our insulation upstand, with this being buried ~200mm down into the stone sub-base.  The expanded metal mesh extends up behind the lower section of cladding and the air gap along that area is filled with stretched out commercial stainless steel pan scourers, to allow air flow up behind the cavity but keep vermin and bugs out.

 

We were given this specification long before the foundations and house were built; IIRC the need for this came from all the passive slab suppliers we contacted.  I think I remember reading something in @tonyshouse blog that he'd had slight rodent damage to his wing insulation.

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We're doing an insulated raft basement. No issues. What he's talking about ground temp is nonsense. Yes, ground temp will be about 7degrees, which means you'll have a consistent temp delta and heat loss, meaning you still need to insulate!!

 

One word of warning re ICF and basements, I've had issues finding a tanking solution. As you can't check the concrete pour for completeness, and the joining webs are potential water bridges, using a waterproofer in the concrete can't be used as a reliable barrier. So if you want somebody to provide a guaranteed system, they will push you to an external barrier membrane as well as an internal cavity system. Fortunately, I've found a builder that will use a single system and is happy to provide the 5yr warranty.

Edited by Conor
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@Conor - re: the ground temp thing, this is exactly my understanding as well. thanks for clarifying that my thinking was not the self-build madness virus taking hold ?

 

Yes, shall be avoiding waterproof concrete. Seems that unless the concrete manufacturer pours and guarantees the stuff themselves, and it's not left encapsulated in something (like it is in ICF), any warranties are relatively pointless.

 

 

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Our rendering contractor said steel mesh can cause problems with adhesion of the render to the eps as well as leave the render exposed to corrosion damage to the mesh should any of the galvanising become damaged during installation.

 

We installed a fibreglass mesh which was fixed to the EPS and then rendered over. 2+ years later there is no damage whatsoever. Fibreglass apparently resists burrowing rodents.

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1 hour ago, ryder72 said:

Our rendering contractor said steel mesh can cause problems with adhesion of the render to the eps as well as leave the render exposed to corrosion damage to the mesh should any of the galvanising become damaged during installation.

 

We installed a fibreglass mesh which was fixed to the EPS and then rendered over. 2+ years later there is no damage whatsoever. Fibreglass apparently resists burrowing rodents.

If rodents gets through your render 

they will make quick work of the fibreglass 

Though I can see where he’s coming from with the steel mesh 

Much easier to lay fibre mesh on 

 

 

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Not sure about fibreglass, but one of the things I looked into when thinking about a rodent barrier around the slab was using buried crushed glass.  Our borehole has bags of crushed glass poured in around the outside of the lower section of perforated pipe, and one of the borehole chaps mentioned that it was good for stopping things digging.  Also works to keep slugs at bay, apparently.  They don't like crawling over it.

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2 hours ago, BotusBuild said:

Yes, shall be avoiding waterproof concrete.

If you need a house warranty (peace of mind, mortgage, re-sale in < 10yrs) then you may want to check with your warranty company. In my experience (limited to my current project) they will not warranty below ground waterproofing so if you are thinking to get a warranty then you may need to use a waterproofing co that can provide a suitable warranty for the product + workmanship. If using EPS (or XPS of course) this limits your options. Some (Sika from what they told me) don't warranty ICF any more - my guess is some early bad installs led to too many claims. Some others will provide a warranty (insurance backed for 10 yrs) as long as you use their range of products and an approved installer. As part of this I would strongly expect you to be using waterproof concrete + an external barrier or an internal cavity drain (hate the idea but is an option). However, a warranty is not something you will ever want to use of course so avoidance of problems is #1, though if the waterproof co both test the concrete and supervises other aspects of the install then you will be on your way to a quality waterproof solution so there is maybe some upside to this approach even if you don't care about getting a warranty.

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12 minutes ago, Adam2 said:

If you need a house warranty (peace of mind, mortgage, re-sale in < 10yrs) then you may want to check with your warranty company. In my experience (limited to my current project) they will not warranty below ground waterproofing so if you are thinking to get a warranty then you may need to use a waterproofing co that can provide a suitable warranty for the product + workmanship. If using EPS (or XPS of course) this limits your options. Some (Sika from what they told me) don't warranty ICF any more - my guess is some early bad installs led to too many claims. Some others will provide a warranty (insurance backed for 10 yrs) as long as you use their range of products and an approved installer. As part of this I would strongly expect you to be using waterproof concrete + an external barrier or an internal cavity drain (hate the idea but is an option). However, a warranty is not something you will ever want to use of course so avoidance of problems is #1, though if the waterproof co both test the concrete and supervises other aspects of the install then you will be on your way to a quality waterproof solution so there is maybe some upside to this approach even if you don't care about getting a warranty.

I concur. I've spoken to pretty much every warranty provider I could find in the UK and none of them will cover water ingress (i.e. basements).

 

I spoke to a few tanking companies and they would provide a guarantee provided their contractors carry out the work, was designed, supervised etc by the company.. One company wanted £1k up front to review my drawings and propose a solution.

 

I've found a builder that will do the tanking himself and include a guarantee as part of the job. Only way I can see of doing it. DIY just isn't an option if you wan to get a mortgage or sell.

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I wonder whether you're allowed to use that method in the UK? Can you combine two of the three defined types (A, B and C in NHBC design document) on the same side of the wall? I'm guessing so as I can't see anything in the NHBC guide to say you can't

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