This was our second self-build; the first was on the Isle of Man over 10 years ago.
The Isle of Man house had a reinforced concrete basement constructed using the Perry formwork system and a factory-built timber frame by Potton on top. The latest one is on the Isle of Wight, but has similarities in that it is on a steeply sloping site on the edge of a village and once again, it has a basement. One of the problems with the Perry formwork and the timber frame on a sloping site is that a crane is required for the duration of the construction, which is expensive. This led us to investigate using ICF for the construction. No crane is required; just a concrete pump for the pours.
After researching the market, we decided that Nudura appeared to have a well thought-out and developed product. Our nearest supplier was ICF Southern who not only supply the product but provide a full quotation from the plans, run training courses, deliver the product and provide advice and support during the construction phase.
Interested in working with ICF Southern
My first bit of advice is to ensure the architect has drawn plans to work with the product dimensions. This can save a lot of time and effort by having window and door openings on aligning with the product’s cut lines and can also eliminate vertical stack joints.
I used a concrete formwork company for the construction. Although they had never worked with ICF before, they went on the course and were very enthusiastic about the product. The system is very straightforward to assemble, as long as the rules are followed, which are clearly explained on the course. I’m an experienced DIY’er and was able to construct the majority of the walls (having also done the course) whilst the team were working on other things. It is vital to carefully check that all the clips are installed on each course.
Having watched several ICF concrete blowouts on Grand Designs, I was naturally concerned about the pour. This is where the experience of the formwork lads came
1. Apparently timber formwork is just as likely to blow out as EPS if you get it wrong.
We simply followed the rules and advice paying particular attention to the corners and the openings. Plenty of 18mm shutter ply for reinforcement is money well spent.
The steel reinforcement system for Nudura is cleverly thought out. The horizontal rebar requires no wire tying, it just clips into the webs. The vertical rebar doesn’t have to be tied, but my team thought it better to put a tie at the top just to make sure the concrete didn’t move them.
Another tip is to make sure you have all your wall penetrations for cables and pipes in place before pouring. Small holes aren’t difficult to drill afterwards (as long as you don’t hit rebar, but core drilling a 110mm soil pipe hole is no fun at all. We had ventilation ductwork up to 200mm and drilling that afterwards doesn’t bear thinking about.
Nudura has a clever wall alignment system that also acts as a walkway for the concrete pour. This was hired from ICF Southern who also checked our construction and reinforcing by video call prior to pouring. We had three pours and they all went perfectly. I left this job to the experts; handling the hose of a concrete pump is like wrestling with a live python but my team were used to it. I just went round checking for any signs of a blow-out, but I’m please to say I was redundant.
We used standard forms with a 200mm core for the basement and XR35 with a 150mm core for the house on top. The details of this junction are not in the construction rules, so we had to use a little ingenuity. The basic rule is to line up the exterior face of the core between the form types which then allows the external faces of the Nudura to lock together. The rest is sorted out with timber and steel straps.
So how does the ICF perform in the finished house? The XR35 has 100mm of EPS on each side of the core, so the insulation level is excellent. Where it does score over our previous timber frame house is thermal mass. Once heated up, the house loses heat more slowly due to the heat stored within the concrete walls (and floor). This means we can “charge” the house up with the heat pump and underfloor heating in the early hours on cheap electricity and the temperature will only slowly decline during the day. It’s almost the old night storage heater principle, only much better. We might need a little boost to the living areas around teatime if it’s really cold outside.
Would I recommend Nudura for house construction? If you want an airtight house that’s economical to heat, very strong and with no chance of rot, then it’s a definite yes. Would I ask ICF Southern to supply again? I certainly would.
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