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Understanding R-Values / Building with ICF

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Understanding R-Values / Building with ICF

Posted 04 Jul '09 06:51 AM

Hi all,

We are about to start building a new house shortly and I'm trying to get my head around a couple of things.

We have decided to build with ICF as we are in a very high wind zone where horizontal rain is quite common (Do I need to say "Wellington" at all?) ;-)

We are looking at both the 200mm Eco block and the 200mm block from Ambionse. The Ambionce block has a r-value or 3.0 and the ecoblock, an r value of 3.5. I believe the difference is due to the width of the poly. The poly on the ecoblock is 65mm thick and I believe the ambionse block is less (i don't know the thickness)

I know the R value increases when gib is installed. Eco block state a r-value of 3.5, rising to 3.78 when the gib is installed, so I am assuming gib has an r value of 0.28. I can't find similar information for Ambionse.

I know a higher r value means more insulation. I'm having trouble working out what the actual difference will be when we are living in the house. Will the extra cost in using eco-blocks will translate to lower heating bills (and how much) or the general ambient temperature in the room?? Or something else??

I'd appreciate your feedback :-)

Re: Understanding R-Values / Building with ICF

Posted 04 Jul '09 08:16 AM

Hello Anon, Are you using a 200mm core for structural, sound (DB) or additional thermal mass requirements? If only for thermal mass, I suggest you reconsider the alternative option of 150mm core for a decent cost saving. Now spend the saving on one or both of these options: As you know, a little less than half the internal energy is lost via the ceiling and just under a quarter via the walls so boost your ceiling insulation rather than trying to gain an additional R0.5 value in the walls. You will not be able to discern the difference. Further, economical wall insulation gains can be achieved by using 50mm timber battens at 600 centres fixed though the 65mm insulation into the concrete core, additional insulation added into the cavity or maybe foil (check manufacturers approval) with 12-5mm or 16mm Gib. Bd linings. Approximately +R1.0 can be gained for little additional cost. The R value for Gib. Bd. is the same for both block suppliers so if the cost is similar then the 65mm ICF block is the better value. Rex

Re: Understanding R-Values / Building with ICF

Posted 04 Jul '09 08:29 AM

What R-value did you have in mind for you windows ?

Re: Understanding R-Values / Building with ICF

Posted 04 Jul '09 09:24 AM

I believe Ambionce has 50 mm poly blocks, the R-value being in the poly, not in the concrete. Will be interested to find out what the difference (in %) will be between the two systems. I am about to choose polyblock for a steep Wellington site, using 200mm core for foundation/retaining walls and 150 mm cores above, My choice for IFC is lightweight meterials for a difficult access, good insulation, strng construction and good air tight construction with PVC windows. Cheers, Marcel

Re: Understanding R-Values / Building with ICF

Posted 05 Jul '09 12:05 AM

i think it is going to be 0.48. The windows units are double glazed, Low E and argon filled. We have also chosen upvc as well and are importing the units.

Re: Understanding R-Values / Building with ICF

Posted 05 Jul '09 12:52 AM

I don't know what kind of upvc you are going to get but with low E and argon you should be somewhere around R 0.7

Re: Understanding R-Values / Building with ICF

Posted 15 Jul '09 05:13 AM

Understanding the R value is basically how long a product can resist thermal movement and retaining an ambient indoor temperature, whether it be cold or hot external conditions. The higher the R value the better the ability for the dwelling to maintain ambient temperature without energy input. For testimonials, you might like to take a look at the Cornerstone Building system http://www.4-cornerstone , as their R value is far higher with the 200mm panels being 4.3 and the 250mm being 5.75, because they concrete post and beam structure poured much the same as the poly blocks. BRANZ rated R value which when calculated out the "concrete and steel" in the system lowered the value. Therefore less concrete higher R value... The other significant difference is that the Cornerstone building system goes together much faster than the block. The poly block is the better option for any retaining required. Cornerstone pricewise is quite a bit cheaper. It also has a high bracing rating twice that of timber frame and is a flexible system but not as flexible as timber. Back to R values. With solid wall construction the requirement is for an R value in the roof area. You may need to spend a little extra on plastic window joinery and double glazing so that you don't have any leaking mitre joints as has been common with aluminium and thermal properties. take a look at and

Re: Understanding R-Values / Building with ICF

Posted 15 Jul '09 05:21 AM

Hi Anon I meant to say that the R value required for solid construction calls for 3.6 in the roof space. and miss guided you on the website for Cornerstone Building system. it is I beleive they won the Master Builders Award for Department of building and Housing under $500,000 award for sustainability and the Pink Batts Energy efficiency award which is in the DBH Codewords newsletter and on Cornerstones own newsletter section.

Re: Understanding R-Values / Building with ICF

Posted 31 Jul '09 02:29 AM

have build with cornerstone in the past and have also joined the long queue of victims taking this company to court...firstly the r value of these buildings might be higher than average, but the material itself does not allow for any moisture to escape out of your house. the result is a very damp enviroment (ideal for mould growth) which is near impossible to heat. we had 42kw of heating in a 170sqm house and still didn't manage to get the place warm in winter! and of course secondly-the price we were quoted by cornerstone was a country mile from what this company tried to charge us towards the end of the project. and last but not least-cornerstone never finished the project so we could not get a code of compliance for our house. we had to pay an independent builder to mop up cornerstones mistakes and in the process found out how many shortcuts this company took. also be weary of using polystyrene building products, as this requires special insulated wiring which will increase your building cost. good luck with your project

Re: Understanding R-Values / Building with ICF

Posted 31 Jul '09 02:48 AM

Should have been obvious that building with a product that provided a sealed environment, would also require correct extra external controlled ventilation. This should have been installed when the house was build and brought to your attention by your architect or the company building the house.

Re: Understanding R-Values / Building with ICF

Posted 31 Jul '09 10:17 AM

To anon @ 2 posts above

As someone who is almost at the build stage using the cornerstone system, I find you post somewhat alarming.

For what reason are you taking them to court? As the poster 1 above says - surely your architect should have known about ventilation. The NZ regs demand 0.35 changes per hour. How did you expect to achieve this, just by opening all the windows?

Can you point to evidence of "the long queue of victims taking this company to court"? If not, be careful what you post as forums do fall under the libel laws.

Regardless - the simple fact is that people need to be much more involved/engaged with the house design/building process. The costs involved are high so it pays to invest time to get things right. Would you buy a modern car without heating or air con? probably not. What if it had no way to ventilate the cab at all? So why do people put up with houses that are designed and built this way?

As my own plans are held up at council at the moment until more bracing information is supplied, my opinion is that NZ building code is very skewed toward strength and rigidity of the structure. There is a very good reason for this, we live in a windy and wobbly country. BUT we also live in a damp, temperate-to-cold country. So until the code focuses more on constructing warm and healthy homes like the Europeans do, then we don't get the standards up and people like yourself have the unfortunate task of picking up the pieces when it all turns to custard.


Re: Understanding R-Values / Building with ICF

Posted 04 Aug '09 02:16 PM

Interesting??? "Cornerstone building system" is not a building company but rather a product, a structural wall system requiring cladding just like timber frame construction to weatherproof it. Polystyrene also breaths so allows internal moisture out. Be careful comments of this nature, the question was about R values wasn't it?

Re: Understanding R-Values / Building with ICF

Posted 06 Sep '09 09:12 AM

Hi I cannot answer your question but I also live in Wellington and have become very interested in building in ICF. There only seems to be the two products, Ambionse and Eco-block, on the NZ market. Ambionse seems to have been around longer and more builders understand it, butEco-block seems to have the advantage in that it can be used for an insulated first floor, something that is of interest to us. It's not the question you asked, so this could be hijacking your post (in which case I apolgise and will do my own post), but I would be interested in understanding the pros and cons of the two systems. I have no idea of the price difference between the two items. I would be very happy to shout a coffee in the Wellingtn innner city area and compare notes.

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