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Infiltration rating of ICF

user-1012653 | Posted in Energy Efficiency and Durability on

I am working on a design using ICF for a new building. I am wanting to run some performance testing on the wall assembly, however I am not exactly sure what to put for the infiltration numbers. Knowing PH is .6, I have been using 1.5 for tight framed construction (hoping and assuming it can test lower), but what is a good number to use for ICF construction from footing to roof? All the rave is about the tightness, so is 1.5 safe or too high? I am also using the r value for the EPS for my number and not any “thermal mass” fluff as they like to claim.

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  1. GBA Editor
    Martin Holladay | | #1

    You can use any number you want for your design, but the number you choose won't reflect reality unless you have a builder who can achieve your specifications.

    It's possible to build a very leaky ICF building, or a very tight ICF building. If you want the builder to achieve 0.6 ach50, put it in the specs -- and choose a builder who has already achieved that number on a previous project.

  2. user-788447 | | #2

    Walls are only one of the many components of the complete air barrier. Using ICF makes it easier to achieve air tightness in the field of wall but in the field of the wall is one of the easiest components to detail. Your window selection, how you detail protrusions, your roof to wall connection, etc all will be important.

    Based on some recent experiences I don't think it is too difficult to achieve 1.5 or lower. Most of the responsibility first is on you the designer of the details. The builder can only accomplish good air tightness with good details. General building practices probably aren't enough to rely on to get down to 1.5 ACH.

  3. user-1012653 | | #3

    This is an old thread, but I figured I would bump it up. I have completed my ICF home and have lived in it for nearly 1 year. The air tightness tested out at 1.02. I have been documenting the years weather in my zone 6. The winter last year was one of the coldest in the last 20 years, so it was a good test to see how the solar tempered home would perform. I am quite pleased.

  4. Pascalli2 | | #4

    Jesse - thank you for posting a follow-up to this original posting. So many times, I have found myself reading through a forum post or Q&A, and wondering how things turned out.

  5. jackofalltrades777 | | #5

    Being that the walls are R-23 due to the EPS, has the concrete thermal mass contributed to any of the good results? An R-23 wall in a Zone 6 climate is OK but you stated that you are "quite pleased" with the results. I would assume a wood frame R-23 wall vs an ICF R-23 wall have two different results in the real world.

  6. user-1012653 | | #6

    First off, despite living in an ICF home, thermal mass in zone 6 has very little impact. There are plenty of studies and tests floating around to prove that, which is something I never bought into with company marketing hype for ICF. Warmer climates? maybe a slightly better story. The ICF I used is actually an r28 whole wall average. More foam than usual, and less concrete. During building design I calculated using that number in relation to other frame wall alternatives ranging from SIPs, double stud, thick foam, etc. Strength, quiet, fire, mold and rot resistant, speed, and inheritingly tighter were my reasons for selecting it. While I can not compare the performance to similarly built higher r and tight homes, I can compare it to my neighbors homes that are built barely code min 2x6 w/ batts. Most at least upgrade to blown. They are starting to put a thick 3/4" iso on the exterior of them now too around gas last winter would 50-60% less than theirs was. The home did receive a HERs rating of 37.

    1. Dustin_7022224 | | #8


      Did you consider adding any additional exterior insulation to your walls? Based upon Dana's comments, it doesn't seem like it would have added any appreciable benefit. I'm building with ICF in zone 5 and am thinking more now about passing on adding any exterior insulation over the ICF.

  7. Expert Member
    Dana Dorsett | | #7

    PeterL wrote:

    >Being that the walls are R-23 due to the EPS, has the concrete thermal mass contributed
    >to any of the good results?

    How do you come up with R23?

    ICF vendors are fond of specifying Type-II EPS at it's 40F temp performance which is about R4.5 per inch, compared to R4.2/inch @ 75F. But with the temperature being a center-depth temp, not the surface temp, that R4.5/inch is only close to being valid when the interior is say +70F, and the outdoor temp is +10F (and the concrete in the middle is about 40F.) A typical ICF is 2.5" + 2.5", for 5" total of Type-II EPS, with a rated R of R21, not R22.5 rounded up to R23. You can legitimately add another R1 for the concrete + gypsum, ending up at R22 for a "whole wall" R you'd have to make the temperature up-rating argument for specific average outdoor temps to hit R23.

    Jesse Lizer's neighbors with 2x6 16" o.c. batt insulated wall with 3/4" of iso comes in at about R 18-R19 whole-wall when you factor in the thermal bridging/sheathing/siding, etc., and using the labeled R-value of the iso (about R4.5-5). But in cold climates like US climate zone 6 or colder the iso needs to be derated to about R3- it's performance sinks fast at a lower center-foam temp less than 35F. That brings the whole-wall performance down to about R17 whole-wall in a zone 6 climate, provided the batts are installed perfectly, and the sheathing is air-tight.

    A more comparable stick-build to the minimal 2.5" + 2.5" ICF would be 2" of EPS sheathing insulation on 2x6 cellulose or blown fiberglass wall. Unlike polyiso which de-rates with falling temperatures, the EPS will perform at or above it's rated R during cold weather. But of course, an R17 wall will always underperform an R22 wall by quite a bit in a cold climate, and an R28 wall will have a significant edge. The R28 ICF will have half the wall losses of a 2x6 wall with no exterior insulation, but the wall losses won't dominate the total heat load numbers once you're over R20 or so.

    The mass effects are still relevant to the peak heating loads in zone 6, since the diurnal swings in temperature of the concrete are severely damped, relative to the outdoor air temp. While R20+ walls are no super-insulation, in most homes with ~R20-R23 whole-wall performance the window losses will exceed wall losses unless you spring for very high performance windows, making the wall loss numbers a smaller fraction of the heat loss even without the mass effect, but the mass doesn't hurt.

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