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For those interested in ICF construction

Posted by ICFgreen (My Page) on
Thu, Feb 23, 12 at 9:50

As an FYI to people interested in building with ICF (Insulated Concrete Forms)...

We just moved into our newly constructed house. We build using ICF partially for sound-proofing and its inherit solid construction, but also for energy efficiency.

Until yesterday we didn't really know how efficient the construction was - we had a modeling done before - but we just received the outcome of our actual Home Energy Rating and here is our number: HERS Score of 41.

This is for a house with a conditioned space of > 5000 sq.ft and without the use geothermal or solar assistance.

While it will be pretty expensive to change the building envelop of house, we still have the option to add solar assistance in a couple years (if and when the prices come down a bit more).

However, the extra price for a geo unit - even after a 30% tax break - combined with the low energy cost of a low HERS score house puts the pay-back period for geo into the 20 yr plus realm meaning that for us that's not an option.

Here is a link that might be useful: HERS Score post on our blog


Follow-Up Postings:

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RE: For those interested in ICF construction

........and just to be fair, more efficient, higher insulated homes can be constructed with sticks and SIPs for a lower cost. For example, you rarely see any net zero, super insulated homes made from ICF. If so, they typically have to add extra EPS foam on the exterior to increase the r value from a typical r24 range of the standard forms.
However they do not come with some of the other advantage of ICF, which is sound dampening, fire and storm protection, bugs, etc. There are disadvantages to the system, as with any. Such as not easily modified later as wood would be. And of course the higher cost of construction.

But its great to see your efficient home (I have been following) is turning out exactly as you were hoping, and more! It is still more efficient then most new homes (especially on this site). Thanks for sharing with the community as usual.

Great HERS score btw! Do you have any blower door test results?!


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RE: For those interested in ICF construction

Good to hear ICFGreen. We have been building our 5000 sqft ICF home ourselves for almost 3 years now. DH got sick (cancer) during the build, but now with a clean bill of health things are moving along and we are into the finishing details. We loved the product. It was great to see when we were doing the drywall and mudding we rented a heater (Canada climate) to regulate the temp. upstairs as we commissioned the radiant floor for the basement. Our electrical bill was high I thought (almost $200 bucks) but then some friends of ours whom are building a standard house had a bill 4 times that amount. Some factors because he needed more than one heater where as our one heater handled the load and then some (we have some 15 foot vaulted ceilings). I really have been impressed with ICF building glad we chose it! Sound dampening alone is a deciding factor for me as the house we live in now is horrible, the kids next-door sound like their playing right in my bedroom!!!

Your home is beautiful! I've been following along your process. Thanks for the review!


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RE: For those interested in ICF construction

lzerarc - I would venture to say that homes on this site are actually more efficient than the "average new home". Since people have more control, more money and do more research than average. As you know, a lot of new homes are built in the South where your idea of home building is pretty foreign (for good reason).

While I understand the sound dampening, I just don't get the need. Seems like brick or stone does a good enough job that windows are your big entry points anyway. I suspect a lzerarc style double wall is also good enough that windows are the big problem.


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RE: For those interested in ICF construction

in highly insulated homes (I will say the bidding starts around r-25 in heating climates and up) depending on the window type and orientation, you are correct. The window will be the bigger loss of heat. However with fiberglass triple pane prices nearing the price of a standard window such as an Andersen 400, it is a way to get a higher performance out of the glass. Also selecting high SHG glass on the south can make the window a heat gain net positive, depending.
The last couple of energy models I have done showed the double pane u .28 windows losing about half the heat load for the exterior walls, the r-30 insulated walls losing the other half. Windows are approximately 5-15% of the shell on most homes, so yes, a large part of the heating bill.

The straight up r value of ICF is not really contributing to the energy savings, and in a heating climate, especially the mass. In heating climates, your r value of your EPS is basically the whole wall r value. "Mass effect" in climates with non-diurnal temps is negligible, as proven by several case studies. The true efficiency of ICF relies on the next to 0 air infiltration, especially when used from footing to roof like the OP is. The air loss details now shift from the walls to around the windows, doors and roof. Seal these areas, and it will dramatically reduce the in and ex-filtration.


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RE: For those interested in ICF construction

It appears our house is actually even more efficient than we originally thought. The 41 was the worst-case scenario our ResNet rater was able to tell us from the actual numbers. Now that all the calculations are done (just waiting on the physical certificate) we are proud to announce our official HERS score: 38.

To give you an indication what that means in real life: our March gas bill was $7.38 in usage charges (plus the $20 monthly fixed service charge). This is in North East Ohio but we did have a very mild March this year. Note that this is without tankless hot water, solar and geo. We do have a 17 SEER heatpump next to our Carrier ICS 96% multi-stage furnace... ;-)

Here is a link that might be useful: Official HERS score blogpost - Apr 6


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