Just got a plan for a “cottage” that has 2700 sq. ft. The plan calls for the exterior walls to be ICF which is not too common ’round here. I prefer to build the cottage “conventionally” as labour is more plentiful etc. What I mean by conventional is 2 x 6 (R20) @ 16″ O.C. plus insulating sheathing (R5 or so). The exterior of the home willl be brick veneer with the foundation being slab on grade. So I was wondering if anyone had CURRENT price evaluations (by the sq. ft.) for these 2 construction techniques including labour
THe HO is building this project as a retirement home and I think that the payback will greatly exceed their lifetime if they use the ICF and not significantly add to re-sale. I am hoping someone has this info readily available. Current costs in your area would probably be reasonably close for my area IMHO…..
Thanks in advance
Joe
First we get good- then we get fast !
Replies
SIPs are a great alternative to ICF and can be built with fairly unskilled labor if you have someone on the crew who knows a little about what's going on.
Kevin Halliburton
"Do you see a man skilled in his work? He will serve before kings; he will not serve before obscure men." - Solomon
I agree with Kevin. ICFs compared to the simplicity of Sips is pretty much insanity....A Sip house will go up (esp the size of the house you're looking at) quicker than stacking the forms, bracing the crap out of them, dealing with blowouts, then when youre done the pour, looking for something to nail to.....
I just dont get the Icf whole house deal at all. S
I don't get the ICF house thing either.
I think that ICFs and SIPs get thrown into the same
category because they both use integral foam
insulation. But they belong in different categories.
Wood vs. reinforced concrete.
ICFs buildings are really more in a class with the
red iron plus SIPs combination. You can build
stronger and taller buildings.
In my area, if I wanted to build a four story
or higher building, I would have to use steel or
concrete by law, and in that case I think ICFs
would be a good choice.
Thanks for the info- I had not considered SIP as an alternative. I guess I still have the same questions as per my original post- what might the cost comparison be for an SIP wall vs a conventional wall as described. Would the SIP be 2X the cost? . (recognizing there are benefits too!) I am concerned that the HO is going to invest too much $ in a retirement home and not see a return or that the re-sale value will be less than the investment cost.
Thanks again
Joe
P.S. That picture of your son- I hope that he hasn't eaten you out of house and home yet.....<G>First we get good- then we get fast !
Buy the Michael Morley Structural Insulated Panels (ISP) book for sale here on this site.
Worth to have it even if you decide against them.
The cost here last June, when I inquired about building with them, was only 5% more than regular stick built houses (I had bids for both). The builder that quoted that was also the fabricator of the panels and trying to promote them. The price included adding borox to the foam to protect against insects.
Like all things, cost is going to largely depend on your location but here in Texas Rubie's 5% seems to be pretty consistant. 5% can be made up in energy savings pretty quick.Kevin Halliburton
"Do you see a man skilled in his work? He will serve before kings; he will not serve before obscure men." - Solomon
I am a huge fan of ICFs, but there is a hidden cost to those thick walls depending on your area. Many property tax appraisers and building departments calculate square footage based on outside dimensions rather than inside. That drives up permit fees and annual property taxes for the same amount of living space.
Appraisers and assessors use the outside square footage because that's the correct method. It's called the architectural square footage. I believe it's to the outside of the foundation, but, in any case it's spelled out precisely in law. It's done the same way for everyone so the statistics are correct and can be compared fairly.
The method of calculating square footage for tax purposes varies by county in most states. The method of calculating for advertising real estate varies all over the map — to the point that realtors in my area include a disclaimer that they got the square footage number from the owner and aren’t responsible. Realtors have been trying to get an ANSI specification for years with little success. See: http://www.nahbrc.org/tertiaryR.asp?TrackID=&CategoryID=1708&DocumentID=1408
It would be very misleading for a buyer of a rammed earth or Adobe home to expect to be able to get their furniture into a house they expected to be comparable in living area to a stick frame home with the same outside dimensions.
Some jurisdictions allow you to adjust for extra thick walls like ICF, rammed earth, and Adobe. Some count unconditioned space at a lower rate. Some allow you to deduct all or part of stairwells leading to unconditioned spaces.
A fair comparison would be specify the amount of habitable space, machinery space, and garage and other non habitable space — like ANSI is trying to do. It makes no sense to me for the county to financially penalize for high energy efficiency or greater fire resistance.
>It would be very misleading for a buyer of a rammed earth or Adobe home to expect to be able to get their furniture into a house they expected to be comparable in living area to a stick frame home with the same outside dimensions.
Excellent points. And imagine the difficulty of calcing domes. My tax assessor had no clue where to start. He showed up with a tape measure and a quizical look on his face.
One appraiser told me that their standard is counting any space with headroom of 5' or more. There are pros and cons to that. It often lowers space counted for taxes. But it also lowers space counted for selling.
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Re ICF: The part that bugs me is the interior insulation. That actually reduces the energy effectiveness of the structure. I know it's there to hold the concrete, but it serves no other purpose and actually hurts energy usage a little bit.
Re SIPS: None of the thermal mass of ICF or other mass wall assemblies.
Everything has it's pluses and minuses...
Interior ICF insulation doesn't always lower the efficiency of the structure. Thermal mass has relatively little value where the difference between average daytime and nighttime temperatures don't vary much or when outside temperatures stay below or above inside temps for weeks at a time. Inside ICF insulation helps heating response time, but reduces the ability to store solar gains.
Houses in general are fantastically complex thermodynamics models.
http://www.buildinggreen.com/features/tm/thermal.cfm covers this kind of stuff pretty well in more detail than I got into in a short post. They've also published test results for different assemblies and different temps. It is complex, but it is also shown from the testing that an insulation-mass-insulation wall is typically not as effective as an exterior insulation-interior mass assembly. That said, ICF offer superior performance to typical stud walls. Pros and cons to each assembly. And places where the differences between assemblies are more and less exaggerated.
I'll defer to this report, be/c they study it a lot more than I do: http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/index.html
Here's an excerpt:
Figure 5 shows the relationship between wall material configurations and DBMS for ten climates. A one-story ranch house and two R- 3 m2K/W (17 hft2F/Btu) walls were considered. One wall had a concrete core with insulation placed on both sides and the second wall was built with concrete on the interior side and insulation on the exterior. The first wall exemplifies popular ICF systems used in the U.S. and Canada. The second wall could represent a concrete block wall insulated with external rigid foam sheathing. Figure 5 clearly demonstrates significant differences in energy performance between the two wall systems. The wall with external foam insulation (Intmass on Figure 5) was much more effective than the ICF wall. The most favorable climates for both wall systems were in Phoenix and Miami and the worst locations were Minneapolis and Chicago. However, even for the worst locations, the DBMS values were close to 1.5. The range of DBMS values for walls with exterior foam insulation (DBMS - from 1.4 to 2.8) is much wider than a very flat chart of DBMS values for the ICF wall system (oscillating around 1.5). This is caused by different distributions of mass and thermal insulation in these walls, generating significant differences in DBMS values for the same climate.
I have seen this study, which is based on computer models and not actual structures. There has been a great deal of criticism over the model and methodology. However, even in this analysis, the difference in overall wall performance is very small between all the insulated thermal mass systems when compared to stick frame. Practical considerations wall finishes, attachments, geometry, and solar gain are also part of the equation.
If you're saying that an ICF wall is less effective than a wall with the same amount of insulation but all on the outside, I believe that. If you're saying that removing the inside insulation on an ICF wall will improve its performance, I have a hard time with that.
I'll vote for option A. I don't know about option B, and since it's never come up as an practical alternative, I haven't seriously looked at it. The conclusions by ORNL seems to be that if you have a mass wall, insulate it to the exterior. I'll let ORNL defend themselves on their testing methodologies. Hope that's a reasonable summary.
Joe,
I've found that ICF adds about 4% to the overall cost of the house compared to 2x6. You certainly make that back in energy efficiency and comfort, how long depends upon your climate.
DRC