As we continue the process of designing and building our home, we are at the stage where we are faced with making decisions. Our first big choice is critical to the rest of the design and has a big impact on the overall cost. The building envelope, otherwise referred to as the wall construction type, is a high cost item, and can affect aesthetics significantly. One of our goals is to create a design that is sustainable, and for an exterior wall, that usually equates to energy efficiency.

Insulated concrete forms (ICF) offer a high level of energy efficiency compared to traditional ‘stick built’ wood framed walls. ICF construction is essentially a concrete and foam sandwich which is put together like a set of Legos on site. Once the foam blocks are in place, concrete is poured in the center cavity and allowed to set. This forms a sound structure with excellent thermal properties. The disadvantage of this type of construction is the overall wall thickness; ICF walls tend to be very thick, and total wall assemblies (the structure plus interior finish and exterior cladding) can be upwards of 14 inches thick. It is easy to see that choosing ICF means giving up some interior space to the wall.

insulating concrete forms

insulating concrete forms (Photo credit: Frameform)

For our design, space is at a premium. We are on a relatively tight lot, and every square foot counts. During our late night study break, we took a walk and ended up discussing ICF as it relates to cost and square footage requirements. What we discovered was that at high level, ICF demands not only a cost premium, but a space premium. Here is what we worked through:

Using basic averages for our design, the house has about 620 linear feet of walls. If we multiply that out by 12 to convert feet to inches, we get 7,440 linear inches of wall. Next, we looked at the delta between an ICF wall thickness and a SIP (structural insulated panel) wall thickness. SIPs are similar to ICF walls in that they are a sandwich of foam and sheathing; typically a wood sheet is glued to the foam, or some types use steel studs (which is the kind we are considering). Basing our numbers on the products I’ve seen, there is a difference of about 5 inches between the two product types. That means for every linear inch of wall, we give up 5 inches of depth if we choose ICF construction. Length x width reveals that we lose 37,200 square inches to ICF; breaking that back into square feet for easy reference means we give up almost 260 square feet of space if we build with insulated concrete forms. That space is eaten up by the walls, and we’ll never get to enjoy it beyond the energy we save (i.e. dollars not spent on electricity).

The next big item we looked at was the cost of the lost square footage. If you build it, you pay for it, even if you never get to ‘use it’. For us, we multiplied out the cost for an ICF house by the lost 260 square feet and realized we would be spending a whopping $41,600 on lost space! Then we had to also account for the increased cost of ICF compared to our SIP alternative. The product I’m considering boasts that it comes in at half the price of ICF, so the delta between the two wall options means we’d spend an extra $20,000 to go with ICF over SIPs. Add the two numbers together, and we’d pay over $60,000 for lost space and the same R-value (which tells us how energy efficient the wall is). The increase in cost between the two walls types alone isn’t terrible, but once we account for the lost space due to increased wall thickness and look more closely at the two products side by side, we don’t add a lot of value for the increased cost.

Residential Application - Before

Residential Application – Before (Photo credit: PorterSIPs)

Granted, we may lose out on some sound transmission advantages and additional natural disaster resistance, but conceptually, a well made and properly installed SIP wall should perform on par with an ICF wall at a much lower cost – both financially and spatially. When it comes down to energy efficiency, we wouldn’t see any kind of significant savings going with ICF compared to SIP, as the cost broken down over time would take decades or even centuries to pay back.

Finally, as our builder pointed out, we would also need to accommodate the added weight of the ICF structure on the foundation. That means a costlier foundation design that requires more engineering and more material (concrete, re-bar, deeper form work, deeper excavation, etc.). One decision quickly affects a host of other components.

Now that we’ve taken a high level look at the hidden costs of ICF, we can start to see that paying a lot more for lost space doesn’t make much sense for us. The premium we pay for space in the city only compounds this figure. We’ll be taking a closer look at these wall type choices and doing more research on the pros and cons of each before settling on a final choice; maybe we’ll find something that surprises us. Do you have experience with an ICF or SIP home? Let us know in the comments!

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  • http://blog.SLS-Construction.com/ SLS Construction

    Pretty fair round up of pros & cons for your project – the only thing I didn’t see mentioned is issues caused when the webs don’t line up with interior walls, & trim outs – those can cause some interesting issues for someone not used to them.
    SIPS & ICF’s – expect increased estimates from sparky’s & plumbers – both add a time factor & a new way of doing things
    For my place, it will be ICF’s with a possibility of SIPS for the roof though I will definitely have an integrated slab between my first floor & basement for disaster reasons

    • http://www.architangent.com Brinn Miracle

      Another great point – for anyone who is unfamiliar with a product, it usually means an up-charge. Although the product we are considering has the option for pre-cut raceways and chases, it can still be an issue for those unfamiliar with it. Thanks for stopping by!

      • Les

        I’m a mechanical engineer, and also looking hard at building methods–energy, cost, and space consumption. Two things we keep running into–builders have made lots of stick homes, they are comfortable there–low risk for them–and they often have trouble selecting the ideal ICF block. In your case (like mine) the 4″ concrete with total of 9″ wall thickness might make a big difference in space loss. The second thing–and to me biggest thing is the blind (perhaps) following of R value. This isn’t the only variable, and maybe even a variable of low importance in a wall. Heat transfer thru a wall isn’t a big driver (like the roof,) rather it is thermal mass. In the days the heat goes way up in FL (and TX) but at night it cools off some bit. The mass of concrete is like momentum. It keeps the temperature stable resisting big swings in temperature. A smaller AC running longer easily keeps the slowly eroding cool from the previous night intact, then when the next night begins, again you get a “free” recharge of cool that carries you into the next day again. If it doesn’t make sense, consider air versus water–water has much more thermal mass. Big swings in temperature effect the water much less than air. Foam insulation is mostly air. It changes temperature easily, though doesnt transfer heat easily; concrete and foam both resists the transfer of heat AND resists change in temperature. This is the real engineering value in icf. Without that understanding, icf would make no sense.

        I hope your home is wonderful and exceeds your hopes in all ways. Sorry for my soap box, but too many builders don’t understand the physics here, and their fear of different can cost us big if we don’t understand. Thermal mass, not R value is the point of ICF over stick for an energy/value discussion. Peace–LV

        • http://www.architangent.com Brinn Miracle

          Hi Les, Thanks for your insightful comment. I agree that we have to fight against ‘the way it has always been’. In regards to thermal mass, it is definitely a consideration that all of us should make. You’re right – a big thick concrete wall will retain heat and slowly release it over time, helping to maintain temperature. For our project (in the sweltering heat of Texas, where ‘winter’ is about 40 degrees on a bad day), I was inclined to think that a large mass of concrete would prove detrimental to indoor comfort, since the retained heat would be slowly dissipating inside over time. If a south facing concrete wall is heated all day, I’m not sure that our night time temperatures would be low enough to help ‘even out’ the heat gain on the wall. What are your thoughts on a large thermal mass in hot-humid areas like Florida and Texas? We are pursuing a rainscreen system that will create natural convection and lessen the heat’s effect on the building. The roof choice is next on my list – likely a paver/deck system on top of the structure. Thanks for stopping by!

          • Refer-Engineer

            Hello
            Im getting to pull the trigger on how I build my house in Central Wa. Looking at ICF real close ,But SIP may be the way?
            Im in a fire prone area,I have ton of rock (Big Ones) a few hundreds on a cliff behind me.
            It gets very hot and cold ,so heating and cooling is a issue,
            But electricity is cheap,2.7 cents a k,w, yes 2.7.
            I have not seen much information on SIP. Are they Energy star rated ?
            Will ASHRAE have anything on SIP?

          • http://www.architangent.com Brinn Miracle

            Hi there, you may want to start by visiting http://www.sips.org/ for more information on SIPs and finding providers in your area. Also, you could consider metal insulated panels, which are similar to SIPs but constructed with metal instead of wood. Here are two manufacturers of metal insulated panels. http://texas.transconsteel.com/products/ultraframe/ and http://www.thermasteelcorp.com/ – In reality, SIP and ICF are both good choices, it will likely come down to cost, availability and familiarity of construction technique from your builder. There are advantages and disadvantages to both sides.

  • architectrunnerguy

    Is your anaylsis just done with the exterior wall costs or mixed in with everything else? Your $160/sf ($41,600/260SF), while very low for a whole house, would suggest the latter.

    • http://www.architangent.com Brinn Miracle

      Yes, you’re exactly right. We took the lost square footage and multiplied by the price per SF that we are using for the house to get the $41k.

  • architectrunnerguy

    Ok. Won’t let me reply to your reply so I’ll just tack my thoughts on here.

    Let me start off by saying I’m not a big fan of the thick ICF walls but your $/SF anaylsis relative to wall thickness (260 sf=$41, 600) may be slightly skewed.

    Sure, it’s convienantly easy to take the total cost of a house and divide it by the SF but in your sf/ linear wall thickness you’re still going to have expensive and fixed costs no matter how thick the walls are.

    First off…..Kitchens…expensive, bathrooms….expensive, nice interior finishes….expensive and you still have those costs irregardless if the walls are 1″ thick or 1 yard thick. Many others here too like window costs and door costs will be the same. Or roof costs or that really neat glass tile you like for the master bath. None of which are related to wall thicknessess but can add significantly to the cost of a house.

    And second, you have fixed costs that are entirely independant of the wall thickness. Grading and site work, permits, insurance, sewer and water connections, and yes, your builders fee.

    So, do your math without a kitchen cost, bathroom cost or the stuff and more that I referenced above.
    Your way of crunching the numbers is a little bit like comparing two refrigerators, one for $1000 and the other for $1200, on a 2000SF house but instead of comparing direct cost to each other you’re multiplying the costs difference by 2000SF (it would a be $400,000 “difference”). Silly I know and there’s area involved here but hopefully you get my drift.
    And as an aside, while I don’t know the building costs in Houston, $160/SF sounds very low. Far better to budget high and be pleasantly surprised than budget low and loose sleep. And that’s coming form an architect who, together with his wife, have built three houses for ourselves over 35 years. And we’re STILL MARRIED!
    Doug

    • http://www.architangent.com Brinn Miracle

      Doug, you are right – this was a very preliminary ‘high level’ comparison we did during a walk one night. We came home after discussing it, threw some numbers down and took a look at the big picture (which still remains true regardless of whether you incorporate cost per SF to build the whole house or just the isolated wall system) – ICF wall thickness takes up space that you pay for but don’t get to use. That was our main conclusion, and the delta between just the two wall types was $20k alone (not accounting for the lost space due to thickness). It started to lose appeal at that realization. It’s something that not everyone thinks of from the beginning when considering ICF.

      As for the costs per SF, we’re actually already working with a builder and we’ve gotten our preliminary estimates in at $150/SF including fees (that was also confirmed by another builder we considered). We’ve had a few meetings to date and will get into the details this summer. Most houses here that are better quality spec types can be constructed at $80-100 SF. Above average quality semi-custom comes in around $150 and high end custom usually starts around $200+ for Houston.

      We’ll have to chat more about your experiences sometime – I’m sure you have a lot to share!

      • architectrunnerguy

        BTW, I like your house but I think I’d work to get more identity for the front door. If you have Christopher Alexanders “Pattern Language” he talks about the importance of that in pattern 110: “Place the main entrance of the building at a point where it can be seen from the main avenues of approach……..” (pages 540-544 is the full description)

        • http://www.architangent.com Brinn Miracle

          You’ve pin pointed the element that has bothered us since the beginning. :) We really wanted to have the front door be on the tall stair volume facing the street, but the stairs will not work any other way and must be placed where the door would go. I’ve looked at it over and over, and my only last scheme to try is to make discontinuous stairs between the first level and second to try to squeeze in a straight run portion on the first floor and have it still end in the same place with enough headroom. It was the one program element we couldn’t accommodate without sacrificing other more important pieces. If you have any ideas, I’m all ears.

  • CW

    Wouldn’t merely extending the design of the house out 5 inches solve all the handwringing over “lost space”? Also, I’m told that there are other benefits with regards to hanging drywall etc that should be factored in and why would you not subtract energy savings from your projected costs? I hear the concrete helps keep houses significantly cooler in climates like your… I am getting ready to build and am leaning towards ICF !

    • http://www.architangent.com Brinn Miracle

      Hi CW,

      Great questions. For our situation, we are in a small city lot, and that means we are literally building to the limits of the property. We do not have any ‘extra room’ to extend the house into, so the only direction our walls will go is inward. Space is at a premium in our case, and so eating away ‘just 5 inches’ adds up to losing almost an entire room of our house in square feet. If you are planning to build on a large lot, then it would not be as much of an issue for space, but you still pay for ‘space you don’t use’. There is a value attached to that lost space that we have to consider, and for our situation the value is very high. We asked ourselves, “Would I rather have an extra room in the house or thick walls that perform the same as thinner walls?” When you ask it like that, it makes sense to try something other than ICF. As for energy savings, ICF and SIPs construction are very comparable. I have found that SIPs may even give us a greater energy efficiency than ICF (Remember: Each product is different, and installation is a big part too!). The marginal difference in utility savings between ICF and SIP construction would take decades or even centuries to pay back the added cost of ICF. Both are very efficient, so really either one would be a good choice.

  • lynda

    I suggest reading the Building Science (Joseph Lstiburek) opinions on Thermal Mass. A lot of folklore has been passed around by the Concrete Industry. Don’t get me wrong, the building system is still good, but there are multiple layers of costs. All “thick wall” building costs extra in property tax, too.

    (Be careful with a 4″ core of concrete, Les, it is extremely hard to consolidate the concrete, and it’s easy to end up with voids. A lot of ICF contractors use substandard techniques to overcome the problem)

    • http://www.architangent.com Brinn Miracle

      Our builder mentioned the same issue with the 4″ cores. He typically recommends 6″ or larger for that reason. I’ll look into the reading you suggested. Thanks!

  • Laura

    Thanks for your article! I have a question… I read in the second paragraph “Once the foam blocks are in place, concrete is poured in the center cavity and allowed to set.” Then later in the article you wrote “Finally, as our builder pointed out, we would also need to accommodate the added weight of the ICF structure on the foundation. ” So I am wondering if the concrete is poured in the cavity, why would the ICF weigh on the foundation? I must be missing something here. Thanks!

    • http://www.architangent.com Brinn Miracle

      Hi Laura, in ICF construction, much like other wall types, the foundation will fully support the footprint of the wall. That means the entire wall width will rest on the foundation, and the foundation will need to support the weight of the wall. In this case, concrete is poured in between two vertical panels of foam, and that entire ‘sandwich’ is sitting on top of the foundation. As a comparison, we could do the same wall out of wood framing, but since wood is so much lighter than concrete, the foundation would support much less weight. ICF walls will naturally be heavier than other types of construction, and the foundation design must accommodate that extra weight – typically through implementing a deeper foundation with more reinforcing steel (which add cost). Hope that answers your question!

  • Albert

    Has anyone considered the cost impact of using ICF regarding
    property tax assessment?

    Because an ICF wall is thicker and square footage for
    property assessment is calculated using exterior dimensions. If we look at the ICF
    home vs 2×4 walled home and both have exactly the same interior square footage
    (all the rooms are the same size), the ICF home will have a larger total square
    footage when it comes to tax assessment calculations.

    I am having a very tuff time understanding why I would want
    to use ICF now. I understand all the claims
    made regarding the cost savings over time using ICF. Regardless of all those claimed cost savings,
    the bottom line the increased square footage also means increased property
    taxes. With one home using ICF and
    another using 2×4 walls, and both with identical interior square footages. In this scenario, I have not read much
    regarding the cost penalty due to increase property taxes as a result of the
    increased square footage when it comes to property tax assessments Does anyone have thoughts around this topic?

    • http://www.architangent.com Brinn Miracle

      Albert, the increase in square footage from an ICF wall in terms of taxation would be minimal. Imagine a 40×60 house with traditional studs – 2400 SF house total. Let’s say we increase the thickness of the wall by a foot. That means you would be in a 2500 SF house with the added thickness. Not a lot, especially when you consider the tax rate is likely around 3%. 3% on an additional 100 SF is rather inconsequential. However, the benefits of ICF are often comparable to those of a SIP or MIP (structural insulated panels with OSB or metal studs).

  • Cameron Ware

    Interesting article and well written. Since I have completed over one million square feet of ICF in Texas I would like to add some thoughts:
    600 plus linear feet of walls is a large house probably with many rooms and furnishings – basically a non-trivial investment. Thus the disaster advantages of the ICF would be significant since it is several times stronger than your typical SIP and up to 9 times stronger than stick construction. If you are in a hurricane area this fact would matter to most folks.
    The 4 hour UL fire rating of ICF vs. 1-2 hour rating for typical SIPs was not mentioned.
    Superior STC characteristics of ICF 50-60 out of the box were not mentioned. Most SIP STC ratings are similar to stick with foam construction. Higher end SIPs are available that have similar STC characteristics.
    SIPs have done a good job in the market claiming they are half the price of ICF. This have not been my experience. The truth is that your better SIPs cost more than ICF and your typical SIP costs only slightly less than ICF. I know this because I bid against them occasionally. Most of our homes increase the overall cost of the house by a few percentage points when compared to stick construction.
    Rarely do the SIPs have equivalent or equal R-value to ICFs. This is because (particularly for the thinner SIP varieties that your considering) they typically take the cavity R-value and use that for the wall assembly R-value. Actually, most SIPs (except the high end) are short circuited by wood just like an open or closed cell foamed stick-house. Stick builders make the same claim — advertising they have an R-value of 20 when they actually have a R-value of 13 due to the wood. Wood typically has an R-value of 1 per inch of thickness.
    The first net-zero school in the United States is in Kentucky is built out of ICF.
    You might consider talking to a builder who has done both. Regards.

    • http://www.architangent.com Brinn Miracle

      Hi Cameron, thanks for the comment. You have many great points, and I think ICF is still a great product for the right projects. In our case, we simply cannot give up the additional inches of wall thickness and still have a comfortable interior proportion. We’re building to the limits of our tiny infill lot, so we need to make our walls as thin as possible. If we had more room, I would definitely consider ICF in another light for the hurricane resistance and STC values that you mention. In our case, we’re pursing a steel and Expanded polystyrene structural panel that is produced by a steel fabrication company. The quote we got on the wall system, all the interior partitions and all of the joists was quite good and keeps us on track for our budget. I haven’t bid our project to ICF to see the actual difference since we know we can’t use it (space concerns), but I’d be curious to see an actual quote come in for a true comparison. I’ll be learning more about the metal SIP product next week when we meet the manufacturer, and I’m hoping to see more information to validate the claims on STC, R-values and the like. Thanks for weighing in!

  • John Mcguire

    Just a couple of notes from someone who had an ICF home built and from someone who has lived in one for the past 5 years

    THICKNESS – Yes your right the windows are thicker….. but you get a free window seat with every window :)

    FOUNDATION – Arent you doing an ICF foundation ? Most ICF homes are the same wall from the foundation up to the roof

    ENERGY EFFICIENCY – I would in general “ignore” ratings …. they don’t seem to always measure reality very well…and as professional sales and ad man I usually ignore most “HYPE” around efficiency claims.. I have an ICF home , 2800 sq feet…. sits on 20 acres of OPEN farm ground south of Chicago………. I spend about the same to heat and cool this home as I did for an 1100 sq foot home built just 10 years earlier….. and this is even more impressive considering that the ICF home is heated via Propane, vs the nat gas on my previous home…. propane costs 2 to 3 times more than nat gas

    A few things i found out being in an ICF house

    1 – Put in a service panel for small utilities….. a lot of utility companies cant drill thru the walls… for me I had them basically build in a tiny window open near some of the other utilities…..and just finished it over with brick and drywall and foam…… Most phone companies and such can drill thru ICF walls…. unless they hit the rebar then good luck :)

    2- Expect to hear some big POPs in the house……. I’m use to a house settling….. but what i have found with this home is that the outer walls and inner walls seem to settle at different rates….. not so bad that I’m getting cracking in the walls…. but this house will pop really loud sometimes :)

    3 : Local code – My home has some of the foundation exposed above grade…. and in Illinois we had to get a special permit for a poured wall over a certain height…. and since my ICF goes all the way up to the roof I’m almost 2 and a half stories above grade… wasnt hard to get… but the arhitect had to have an engineer sign off and modify the plan slightly

    4 : INSURANCE SAVINGS – In Illinois you get ZERO insurance discount for an ICF home….. I have 8” concrete walls with full brick on the outside…… my walls are almost 12 inches of solid concrete, rebar and brick…. but the insurance companies don’t care…. the only ICF discount you can get is if you are in a hurricane zone… if your lucky they will treat it like brick construction

    5 : QUIET – This house is QUIET – Again I’m on 20 acres of open farm ground….. when its windy as heck out or a big storm is going on I can hardly tell…….. also you cant hear cars pull up to your house…. so get a good doorbell cuz you wont hear them driving up unless your windows are open

    All in all I’m happy with ICF…. it cost me a little more, but not a crazy amount more… and the house is efficient, quiet and well it feels like a real building… and during the big storms we’ve had recently I feel very secure

    • http://www.architangent.com Brinn Miracle

      Hi John, thanks for the great tips/pointers. The foundations in Texas are typically some variation of a slab on grade since we have clay soils and a high water table. No basements or crawlspaces, typically.

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  • Matthew

    Sorry if this seems rude, but your linear feet analysis strikes me as very large. Forgive me if these seem like condescending questions but I just can’t seem to wrap my head around the numbers. I’m assuming that you’re only using icf on the exterior walls yes? And that you didn’t count the basement because that would require poured concrete and insulation anyway? I can see you arriving at your numbers if you counted all the interior walls of your house (i.e the perimeter of each room) but not if you just counted the outside wall.
    600 linear feet of outside wall would be 2 floors of a 50′ x 100′ house, or if you counted the basement 3 floors of a 50′ x 50′ house. Again, I’m not trying to pick apart your very real point about the lost space, but… 260 sq/ft and $41,000 seems bonkers.

    • matthew

      Oh wow (I’m a dummy), I just realized that this is BLOG and visited the previous post that included the schematics of your house and answered all my questions on my own. Disregard the above post. Beautiful house by the way.

    • http://www.architangent.com Brinn Miracle

      Hi Matthew, our house footprint is approximately 32′ x 58′ and it is 3 stories tall, even 4 stories at the staircase up to the roof decks. We have several places where walls jog in and out to break up the massing, adding up the linear footage quickly. We live in Houston, so we don’t have basements typically. You can see the floor plans on previous posts to get a feel for where the walls are.