ICF performance by zones
Burly
| Posted in Energy Efficiency and Durability on
So I am looking into ICF panels. Currently looking at Amvic systems. My concern is I live on the boarder of zone 5 & 6. It can get really cold -0 and really hot +100. There isn’t much information that I have found that explains where these ICF walls will work well and when they won’t. I have considered SIP panels as well but I think ICF walls will be cheaper and then I’ll put sip ceilings.
Can someone give me any sources to find more info? Or at least your experience in Zone 5 & 6 climates?
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Replies
Matt,
According to the 2012 IRC, a so-called "mass wall" (a controversial category that includes ICF walls), above-grade, needs to have a minimum R-value of R-13 in Climate Zone 5 or R-15 in Zone 6.
If these walls weren't "mass walls," the requirements would be R-20 in Zone 5 or "R-20+5" in Zone 6.
It looks like an Amvic 11-inch wall consists of 6 inches of concrete and 5 inches of EPS. That wall would be rated at about R-20, although Amvic's calculation assume a high R-value per inch for the EPS, and also adds up the air films and assumes a (small) R-value for the concrete, ending up with what they call an R-24.7 wall. Here is the link:
http://www.amvicsystem.com/wp-content/uploads/2010/05/icftesting/RValue%2011in%20Wall%20without%20Finishing.pdf
I'm pretty sure that there are less expensive ways to create a wall with an R-value that is somewhere between R-20 and R-24.
For more information on walls with lots of thermal mass, see All About Thermal Mass. Here's the short version: in your climate, don't expect the concrete layer to contribute to your wall's thermal performance.
http://www.amvicsystem.com/wp-content/uploads/2013/01/Report-ITL-053012-12130-R-Charts-4.pdf
This shows a little higher R-value. Which actually seems pretty good to me. Howeve don't sips have r-values in the r-40 to r-50 range?
I feel like in extreme climates thermal mass would actually work against you? Like you said it's kind of a controversial topic. As much as I have searched just haven't found a good answer to where I feel is solid info. Not just someone's opinion or they have an agenda. Like they are selling the product.
My assumption is that due to the wall being more air tight that gives it a higher effective r-value.... Atleast I think that's what they call it. However in zone 5-7 it might be a better option looking at SIPs?
Matt,
The R-value of a wall assembly is independent of the wall assembly's air leakage rate. While it's true that low rates of air leakage improve the thermal performance of the house, low rates of air leakage do not affect R-value.
Here is a link to an article on this topic: Understanding R-Value.
Matt,
Q. "I feel like in extreme climates thermal mass would actually work against you?... As much as I have searched just haven't found a good answer to where I feel is solid info."
A. In a cold climate, thermal mass provides no benefit. For "solid info" on this issue, read the article I linked to: All About Thermal Mass.
Thanks for the info guys. I'll do some reading! It's just hard to find good info when it comes to my zone and how those building materials effects the efficiency of the home...... I'll keep reading....
The benefit of thermal mass is primarily a benefit in climates with high daily temperature fluctuations. If you're in a high desert, insulated mass walls are a good match. High yearly temperature fluctuations can only be harvested with a complicated concept called "passive annual heat storage" which is a whole different kettle of fish and puts you squarely in experimental territory.
That said, most ICFs in their stock configuration that have mass sandwiched between two insulation layers don't count as mass walls, since the building code definition states that greater than 50% of the insulation must be on the outside. To meet that definition, you'd need an ICF that has 1 or 2 inches of insulation on the inside and 3+ inches on the outside.
Yes. Southern Idaho is in a high dessert. I'm doing a lot of research trying to make a very efficient home. Starting with the shell then working towards everything else.
Matt,
You are getting consistent advice. ICFs and SIPs are expensive ways to build an above-grade wall, and they don't provide any benefit compared to less expensive options.
Most builders in search of a high-R wall choose one of these two approaches:
(a) A double-stud wall insulated with dense-packed cellulose insulation. This type of wall should always have a ventilated rainscreen gap between the siding and the WRB.
(b) A 2x6 wall with one or more layers of rigid foam insulation on the exterior side of the wall sheathing. This type of wall usually has vertical furring strips on the exterior side of the rigid foam to create a ventilated rainscreen gap.
@Martin -
Does your above-grade wall advice (regarding less expensive for similar benefit) apply only to the northern climate where Matt is located? Or for all climates? I'm in northern VA (zone 4).
Adam,
In Climate Zone 4, your walls can have a lower R-value than walls in a colder climate. These days, with energy prices as low as they are, it's hard to know how much money to invest in energy features for a new home. You'll have to make your own calculations and decisions, based on how long you expect to live in your house, and your best guess concerning future energy prices.
Clearly a new home has to meet the minimum R-value requirements in the building code, and it always makes sense to pay attention to airtightness during construction. If you want to delve into these issues further, I recommend this article: Payback Calculations for Energy-Efficiency Improvements.
In zone 4A new construction it's hard to make a financial rationale for much more than a 24" on center 2x6/R20 + R6 continuous insulation type wall, which comes in at about R22 whole wall, counting the wallboard, sheathing, siding, and the interior & exterior air films.
At R22 whole-wall for the wall stackup if you...
...design the footprint with 6 or fewer corners (counting both interior & exterior corners)...
...put R55-R60 cellulose in an energy heel truss attic...
...use R15 continuous insulation on the foundation walls (or stemwalls, if slab on grade)...
...with 2" of EPS under the slab (either basement or slab-on-grade...
....and 0.028-0.30 windows...
... use better class and RIGHT SIZED heat pumps for heating & cooling....
...it's possible to design the house such that it's annual energy use can be entirely offset by a solar array that fits on the roof. This of course presumes that you orient the roof pitches reasonably for solar, don't cut up the south facing roof pitches with dormers, valleys, vents, skylights etc.
That R22 whole wall performance is dead-easy to achieve using 2x6 24" construction using 1.5" Huber ZIP-R sheathing , which has R6 of polyisocyanurate laminated to the OSB. The cavity insulation can either be half-pound spray polyurethane, damp sprayed cellulose, R21 fiberglass, or R23 rock wool, it'll all come in pretty close. When using fiber insulation the cavities need to be air-sealed to the sheathing with caulk prior to insulation. That stackup in a zone 4A location doesn't need an interior side vapor retarder other than standard latex paint on wallboard. Paying some attention to air tightness on the wallboard helps, but isn't as important as air sealing the cavities and the sheathing.
ZIP products are seam-sealed from the exterior using their proprietary tape, but it has a factory-applied weather resistant barrier- it needs no housewrap or #15 felt, just siding. With any siding products that aren't inherently back-ventilated (eg vinyl or aluminum) it's a good idea to build it as a rainscreen, with at least a 1/4" gap between the siding and sheathing. This can be done with 1x4 furring, or strips of OSB cut down and glued & nailed to the sheathing, hanging the siding on the furring/strips.
At the rate solar costs are falling, going any more than that on the building envelope may not have much of a return on energy costs, moisture resilience, or comfort in that climate. Leveraged by a heat pump with a HSPF of 10 or more and an SEER of 16 or more solar at $2/watt (either raw cost, or after subsidies are applied), if net -metered at retail it comes in cheaper than natural gas in most markets. Typical solar costs in 2016 are ~3-3.50/watt, installed, before any subsidies are applied. With the 30% federal tax credit that becomes $2.10- 2.45 /watt. Some states & utilities offer other incentives. By 2020 the un-subsidised cost of rooftop PV in the US should be about $2/watt or less. It already is that cheap in mature markets such as Germany or Australia, which are not cheap-labor markets, and the hardware itself is still getting cheaper year-on-year at a significant rate.