Planning to construct a certified PassivHaus just north of Toronto, Ontario, Canada.
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Currently live in a 2 storey ICF house with a full basement that I built 16 years ago. Really believe that ICF is the only way to build. After doing some research, I haven’t found any passive houses that have been built with an ICF building envelope. Almost all houses have been built with various wood framing systems combined with cellulose or other insulation products. Is there a problem with an ICF building envelope?
Thanks in advance,
Andy Voura
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Replies
Andreas,
There's nothing wrong with an ICF wall, except for the fact that most ICF walls have a low R-value. While ICF walls are typically rated at R-17 to R-23, many Passivhaus homes have R-40 walls.
A few ICF manufacturers make high-R forms, however. You might consider the XRV line from Logix, a manufacturer of ICFs. These ICFs are available with EPS that is up to 8 inches thick. For more information, see New Green Building Products — January 2009.
Martin,
I have been looking at Quad Lock .They have an ICF system that can achieve R-43 and R-59.
Will look into the Logix ICF.
Thanks for your response.
Andy
Andreas,
Make sure that the ICF manufacturer is not exaggerating. The Quad-Lock web site seems to report that the maximum available thickness of EPS is 4.25 inches. If there are two layers of EPS (one on each side of the concrete wall), that makes 8.5 inches of EPS, which results in an R-value of about R-34. I'm not sure how Quad Lock calculates that its ICFs achieve R-59.
Martin,
Looked into Logix and the problem I have discovered is that when using their thickest ICF the webs do not extend far enough to the exterior to facilitate the fastening of the siding.
Quad Lock can increase their R-value to R-43 and R-59 by adding thicker panels of EPS and connecting the panels with various widths of their web system that could accommodate the fastening of the exterior siding. This is what appeals to me even though the ICF must be assembled on site.
Also still trying to figure out how to add enough insulation on the end wall openings for the windows and doors that will not create a fastening issue.
Thanks,
Andy
Andreas,
It looks like you are beginning to realize why few (if any) Passivhaus designers specify ICF walls.
What kind of R values would you need to build this house, i can't imagine it being anywhere near cost effective (though i could be wrong)
Sheet EPS costs about 10 cents per R per square foot (installed). Dense packed cellulose is a bit more than half that. ICFs are more expensive than sheet EPS.
ICFs can sometimes make sense on it's other aspects (structural capacity in tornado alley, "time is money" calendar time, etc.) but rarely on a price/thermal-performance basis.
Beware the common R-value exaggerations of the ICF industry, which often cites a dynamic number based on the thermal mass, which even when the circumstances are accurate, are more important for the peak loads than energy use or average loads. The other commonly found thumb on the scale is to use it's R-value at a mean temp of 40F of R4.5/inch or even 25F of R4.7/inch, which would not be anywhere near your seasonal average conditions. To have a mean temp through the foam of 25F/-4C with an interior temp of 68F/20C would require an average outdoor temp of -18F/-28C. That's a peak low temperature you may experience in the Toronto area once every 50 years or so, but it's not your wintertime average.
It's easier to hit Net Zero Energy with a fatter-than average ICF than PassiveHouse. In Toronto you could probably get to Net Zero with a PV array that fits on the house using a 2.5"+ 2.5" ICF with another 2" - 2.5" of EPS on the exterior, provided you build the rest of the components of sufficiently high performance. It'll be a lot harder to get to PassiveHouse levels of energy use.
The "Passive House in the Woods" in Hudson, WI (just east of St Paul, MN) was built using ICFS--and another 11" of foam on the outside!! http://www.passivehouseinthewoods.com/ http://testudio.com/projects/passive-house-in-the-woods/
An awful lot of foam to get R70 walls. I think the house cost about $500k in 2010.
@Jiim
Thats a bloody expensive house insulation, solar panels would be much cheaper
R70 walls
R8 Windows and doors high solar heat gain (64%), triple pane low-E coated glazings
R60 Slab 12” of extruded polystyrene
R95! Flat roof averages 14” of polyisocyanurate