Spray foam insulating
I have a home that is approx 800 sq ft in size not counting the attic.
I’d like to spray foam it.
It is about 70 years old built with 2×4’s.
Crawl space, no bsmt.
A little over 8′ walls on main floor ( 100″)
I was planning on doing 3″ of closed cell 2LB spray foam from a professional.
Also, as well in the rafters since it is a sloped roof but I’d like the attic finished since it is 7ft high, I would have some nice, temp regulated storage and I am planning to install the furnace there too.
I was then made aware of certain concerns.
1, I was told was that I am not going to achieve the proper R value.
2. I will have thermal bridging issues.
I have had a home before that I had spray foamed with only 2 inches on the walls, and 3″ in the sloped ceiling on 2×4 walls and roof rafters. I did not fill with any extra insulation. I simply closed it with drywall. I did this due to reading this chart in 2014. http://www.dwyersspecialty.com/images/rfairygraph.jpg
From my experience, in the 2 years there, it has been great. My monthly heating bills for this past winter averaged $60 a month. However, it was a very mild winter, and the home is only 600 sq ft.
But, comfort wise, it is really good. I can’t comment on cooling since it has no A/C.
I did 2″ of foam on the outer walls because I read after that the efficiency barely goes up past 2″ with spray foam even though you get more R value on paper, and with the 2″ I achieved a vapour barrier.
Speaking from real world experience, this seems to have been the case and worked well for me.
As well, thermal bridging does not seem to be a problem with my bills or with the comfort level I have there.
Here is a nice article that sums up what I read about before, and after, I had this actual experience.
If I were to equate the R value of the spray foam, I would triple it in real world comparison to fibre insulation from my actual hands on experience.
http://sprayfoams.info/the-r-value-myth/
Now, with this house I am discussing here, I’m willing to spend a little more and do 3″ throughout the entire house.
When I read up on thermal bridging, I figure, doesn’t that apply to standard insulation as well??
Considering how well my previous home has done with spray foam, or so I think according to my comfort level and energy bills, would a similar plan on this house be a good way to go?
Or is there something I’m not seeing?
I am also going to get a couple HVAC quotes this weekend/week.
From a couple phone calls with some HVAC contractors, they mention that I do not need a modulating furnace for such a small home and a 2 stage variable with ECM motor is more than fine and less problematic. ( goodman furnace) I personally would like a York LX. I will compare prices I guess. Would like a quiet one since I’m planning a horizontal attic install above a bedroom and am going to finish the attic for storage and maybe a kid(s) to hang out up there one day. Was thinking on placing it on 2″ XPS foam as well to dampen some noise.
60K btu furnace with approx 15 runs for the home over the phone call. But will give me the real numbers once they see it in person.
Any advice is appreciated to help me make more wise/informed decisions.
Thank you.
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Replies
Mic,
It's hard to give you advice unless you tell us your location or climate zone.
Whatever you decide to do, you have to meet local building codes. Your local code official may inform you that there are no regulations relating to renovation work; if that's so, fine. Otherwise, you may need to consider local regulations that apply.
Assuming that there are no building codes that interfere with your plan, you can do anything you want. It's your house.
The first graph you linked to is deceptive, because it compares heat loss in a spray-foamed house with heat loss in a tent (that is, a structure with no R-value at all). It would be less deceptive to make all comparisons with a code-minimum house -- that is, the worst house that can legally be built. It is not legal to insulate a new house to the level of a tent.
The second item you linked to is a self-serving piece of fluffery designed to sell spray foam by spreading half-truths: "The R-value is a modern fairy tale. It’s a fairy tale that has been so touted to the American consumer that it now has a chiseled in-stone status. But the saddest part of this fairy tale is that the R-value by itself is almost a worthless number."
For more accurate information, see these two articles:
Understanding R-Value
It’s OK to Skimp On Insulation, Icynene Says
From a scientific perspective, here are important points to remember:
1. GBA recommends that homeowners aim to install insulation that at least meets minimum code requirements.
2. No matter what type of insulation you install, it's important that you try to reduce air leakage through your floors, walls, and ceilings.
3. Every time you double the R-value of your wall assembly or ceiling assembly, you cut the rate of heat flow through that assembly in half. Heat will flow through an R-20 assembly at half the rate that it flows through an R-10 assembly. That's physics.
Martin answered the key questions very well.. Here's a little more on some other aspects, while we wait to find out your climate zone.
Thermal bridging affects any insulation installed inside a conventional stud wall. Ways around it include varying the wall construction or installing insulation on the outside surface, rather than inside the wall--rigid board insulation that can be foam or mineral wool.
If thermal bridging affects any insulation type inside a stud wall, you might think that it shouldn't factor into your decision about what insulation to use there. But in fact, thermal bridging means spray foam doesn't make much sense inside a wall cavity. It is really expensive, both in terms of $ and in terms of environmental impact. But the performance is limited not by the insulation, but by the bridging. Even with the cavity filled 100% with spray foam, the overall wall assembly heat flow is barely any lower with spray foam than with fluffy insulation, installed well.
Another thing to consider is that although spray foam almost always works well, when something goes wrong in its application, the result has a nasty lingering odor. In that rare cases that that happens, it's nightmare.
Finally, the gas used to blow the bubbles in conventional closed-cell spray foam ... and also in XPS "blueboard" is a potent greenhouse gas, with 1400X times higher climate change impact than CO2. So if part of your goal is to reduce your environmental impact, it's much better to use other types of foam (polyiso or EPS beadboard), or fluffy insulation. There are spray foams without this problem--open cell foam and a new "4G" foam from Lapolla--but they are still expensive and thus don't make a lot of sense to use between studs.
Oh, sorry.
I am in Hamilton, ON. Canada.
The building code is a min R20 I believe for outer walls at the time I did that house in spray foam back in 2014.
The 2" did not meet that on paper (r12.5 or so of spray foam)
However, the inspector passed it since it met vapour barrier it satisfied him.
From reading, when insulation gets a little damp, wet, or wind is blowing by it, its R value decreases greatly. From hands on experience, this holds true for me.
For example, blown in attic. Humid hot days. Attic is pumped with R60 worth of insulation.
The moisture makes it damp. Decreases real world attic insulation properties 10 fold. r60, now feels like r10.
Spray foam. 3". R value 19
HOT and humid on the outside of the spray foam it is VERY hot humid. However, the 3" hold its true R19 value and vapour barrier with no breaks so no hot cold meets to condensate unlike poly #6 that is punctured the odd spot with a nail or screw, etc...
So when I say foam feels at least 3 times the standard rating of its R value of approx 6.5 per inch, this is why.
I did not get this from a chart. Just an example off my head with inaccurate numbers.
However, please note that I have been in a house like this for 2 whole years now. I am no expert, nor do I pretend to be. If I was, I probably would not have done the min 2" spray foam just to meet vapour barrier standards and call it a day. But I am a real person, in that home, that sees the bills, pays them, and feels the climate, and I can tell you, it is amazing and easily comparable if not better than the new homes I work in after they are finished with standard fibre insulation.
As for the chart.
The chart compares R value of spray foam to nothing? Umm.. well... unless specifically compared side by side to another (insulating) product, I would figure that is a given??? I'm confused.
Yes, no insulation, vs xx amount of insulation on the chart.
When they chart out, say, Roxul, and say R 14, I figure they also mean, as if it had nothing and you add that insulation. But like I mentioned, when wind and or moisture/humidity gets involved, I don't think it'll hold close to R14 unlike sprayed foam from personal experience.
I'm mainly wondering, if I am missing any issues with humidity/condensation issues. Things that can damage my structure, or cause mould down the road, etc...
ie: do I need some kind of poly wrap anywhere since I am doing 3" of foam to blanket the house with I figure I do not. ?
oh, do note that the previous home I was in since 2014 was 100 years old with 2x4 studs. Even if I wanted to, I could not meet OBC code as the studs were not big enough to fill with fibre insulation to meet OBC.
edit:
Oh, Mr Sullivan, thanks for your response.
I have seen it after I posted this.
I plan on doing the siding in the next 1-2 years. So I was thinking of addressing thermal bridging then with foam board.
However, I cannot do much about the roof unless I shrink the attic on the inside. Maybe use some 2" foam board I have and strap that for drywall to be placed.
Yes I've read the environmental impact about spray foam.
It is a real shame, however, I am stuck between a rock and a hard place. I've seen the performance of spray foam vs insulation (properly) installed, and I've felt the bill difference. With costs continually going up, it is hard to ignore.
That number of 1400x is a great cause of concern though.
With such a high initial impact, I wonder why it was approved in the first place?!
Mic,
Hamilton, Ontario gets cold. If you are satisfied with the performance of R-12 walls and an R-19 ceiling, as I said -- go right ahead and insulate to those standards. It's your house.
(And by the way, your walls aren't really R-12, because of thermal bridging.)
You should realize, however, that an R-12 wall will leak heat at twice the rate of an R-24 wall. Similarly, an R-19 ceiling will leak heat at twice the rate of an R-38 ceiling.
If you can afford more insulation, you'll cut your energy bills. (And if affordability is an issue, you should realize that you get more R-value per dollar from cellulose than spray foam.)
You're right that you don't want fluffy insulation like fiberglass or cellulose to get damp. No one advises details that lead to damp insulation, though. Design your house well, and your insulation won't get damp.
The thermal bridging with 2"/R13 of closed cell foam is nearly twice that of R13 fiberglass. In an air-tight assembly the R13 fiberglass will indeed outperform it.
The reason is that for the more thermally conductive path through the framing is only 2" instead of 3.5", and the cold wood extends into the warm side of the cavity as a heat-sink, with more surface area than a stud edge flush with the depth of the insulation. With a species that runs ~R1.2/inch (most structural pine, hemlock & fir, douglass fir is lower, spruce a bit higher) the performance of the framing fraction with 2" of closed cell foam is about R2, less than the R1.2 x 2 - R2.4 due to the heat sink effect, whereas with an R13 fiber fill it's about R4.2.
In numerous design analysis surveys the framing fraction is is typically 25% of the total wall area with 2x4 construction, after you factor in the headers, bottom plates, window framing, jack studs etc., about 30% in areas where code requires mid-cavity fire stops or seismic reinforcement.
With typical sheathing & siding options, adding in the inteior & exterior air films an R13 fiberglass or cellulose wall comes in at about R10 "whole wall", with all thermal bridging and layers accounted for, or about U0.10 BTU per hour per square foot per degree-F difference.
The same wall with 2" of R6.5/inch foam for an R13 center-cavity R comes in at about R8 whole wall, due to the higher thermal bridging. You would get literally the same whole wall performance with less foam by installing a continuous layer of 1" foam over the exterior, and empty cavities.
In your climate you'd be fine with a 1" flash-foam of closed cell, which would air & vapor seal the sheathing with a ~1 perm non-wicking condensing surface, protecting the sheathing, then filling the remaining 2.5" of space with a compressed fiberglass batt. An R13 batt performs at about R10 when compressed to 2.5", so you'd have about R16-R17 center cavity and about R11 whole wall performance. The R value of the materials exterior to the foam/fiber boundary are sufficient to keep the average temp at the foam/fiber boundary above the dew point of the interior air- it won't accumulate moisture over the winter even without interior vapor retarders.
A 1" flash-foam is a pretty expensive ~10% reduction in heat loss but you can do that if you like, and it's cheaper & greener than 2".
A 3" cavity fill of closed cell brings it up to about R12 whole-wall, and has to be done in two lifts of no more than 2" each with a cooling off period between lifts for fire safety during curing and a high quality no-shrinkage installation.
If you're planning to do exterior foam in 1-2 years, the best bang/buck is to air seal the sheathing to the framing in every stud bay and insulate with R15 rock wool/fiberglass or R13 cellulose/fiberglass/open cell solution with a 2-mil nylon vapor retarder on the interior. The 2-mil nylon meets NBC definition for a vapour barrier, but becomes vapor open should moisture inside the cavity rise to rot/mold levels, allowing it to dry into the interior. When you re-side, as little as R5 foam or rigid rock wool on the exterior would be sufficient dew point control at the sheathing, at which point the 2-mil nylon wouldn't be needed, but is fine, since it doesn't create a moisture trap.
The notion that slightly humid feeling fiber insulation loses much R-value is simply bunk. It has to be visibly wet before that's true.
[edited to add]
To air seal a plank sheathed antique wall to be able to use fiber insulation can be done a number of ways. Using a continuous sheet of housewrap that loosely wraps the studs and stapled to the sheathing at the stud/sheathing boundary often works well, and you'd then only have to detail where it intersects the top/bottom plates & window framing, etc.
If it's full dimension studs batts designed for milled lumber framing don't fully fill the void, but as long as it's 16" on center you can usually make it work compression R19-R23 batts designed for 2x6 framing. Cellulose or fiberglass blown in netting works just fine at any stud depth & spacing, and it's possible to do a decent job of it with a single stage box store rental blower if you take your time and read up on how to dense pack. You won't be able to hit 3.5lbs density, but with persistence you'll be able to hit 3+, and it'll rise a bit when you roller out the pillowing/bulge before adding the 2-mil nylon and wallboard.
Mic I won't argue the numbers posted by others above but will instead post my experience like you in living in a foam house. Zone 5 located in NW Missouri. We did 3-1/2" of closed cell in the wall assemblies, 5-1/2" closed cell in the ceiling and covered the rafters where exposed to help with thermal bridging. Insulated vinyl siding was used on the exterior. I posted my build progress from planning to move in on another website. At the time I had several posters tell me that either the foam was not thick enough, I needed exterior foam on the walls and roof for thermal bridging, or that with 3-1/2" walls and 5-1/2" roof the thermal bridging would kill my efficiency.
We moved into the house May of 2014. We have two full winters in the home now and my numbers are fantastic for heating our home, especially given the size. We have roughly 3,700 sq/ft of living space 1st and 2nd floor along with another 1,000 sq/ft of finished basement that is heated occasionally for movie nights or kids on the weekend (stays about 66 degrees year round without conditioning). Our total conditioned volume including basement is just under 52,000 cu/ft. We are running two - 2-1/2 ton geothermal units without backup heat and we are still oversized for the heat load. We could run on 3 tons total without backup heat strips easily. I think one thing most people miss about foam is how idiot proof it is for air sealing. There will still be some areas that get missed and you still need to blower door test but if you are not installing the insulation yourself or doing the sealing and testing, batt insulation ends up with a much higher air leakage almost every time.
JEREMY,
I have the exact same hands on experience like you and I did HALF the amount you did in a ZONE 2 climate and I did not address thermal bridging.
I hold the thermostat at 69-72 depending on my feeling in winter.
It is very comfortable except by the front door from open and close times since it enters right into the living space.
House is ONLY 600 sq ft though ( yes, quite small )
However, it is a gas stove, gas water heater and gas furnace.
Monthly bills this winter averaged $60!!!!
That includes the $21 or so dollar delivery charge here. All in Canadian funds. Convert that to your USD and it's even lower.
So I understand all the numbers posted by D DORSETT and how it makes sense on paper.
But I speak from real world experience.
If I spend double the money to do what is proposed, how much more can I actually save?
Would I recoup, if ever in my lifetime?
$60 a month ( only in winter this yr) vs another $10 in savings monthly?
I even use a Nest thermostat on a 2 stage variable ECM furnace which is also somewhat wrong since I should get a proper 2 stage stat. But I purchased this before I knew such things.
Now, if I can fix my hydro bill ... (darn kid!)
Would it be double the money?
In my neighborhood closed cell foam costs 17-18 US cents per R per square foot, installed. Fiberglass batts run about 6-7 cents , rock wool or HDfiberglass 9-10 cents. Dense packed cellulose about 12-13 cents R-foot (varies wider than that.)
So, if you're installing R15 rock wool instead of R13 you're looking at $1.50 is per square foot instead of $2.25 with R13 foam.
The 2-mil nylon (Certainteed MemBrain) adds about 20 cents per square foot if professionally installed (12 cents as a DIY) so now it's up to $1.70, add 75 cents per square foot for a Tyvek air-barrier detailing professionally installed (a lot cheaper as a DIY) and you're up to $2.45. That's about a 20 cents (~9%) premium over 2" of closed cell, but it's also a ~20% reduction in heat loss. It's nothing like double the money- it's practically a wash.
The result is also more moisture resilient than a 2" flash foam, and has far lower environmental impact.
With plank sheathing may be cheaper & simpler overall to go with half-pound open cell foam, which comes in at about 10-11 cents per R-foot. For milled lumber framing that would be no more than $1.40 per square foot, $1.50 with professionally installed 2-mil and would deliver the full ~R10-ish whole wall R, and it would outperform the 2" of closed cell at a significant discount. (When it's plank sheathing with big gaps and knot holes this is usually the "right" way to go.)
Adding an inch of EPS later would run about 40 cents per square foot, and with fiber or open cell cavity fill it would beat the performance of 3" of close cell foam with good measure, and STILL be at a discount from 2" of closed cell foam.
Open cell foam is blown with water, which is very low impact compared to HFC245fa. Even with full dimension 2x4 lumber a full cavity fill of half pound open cell is still only the amount of polymer in a single inch of closed cell foam, half the amount of polymer as in 2" of closed cell foam.
Anyway you slice it, installing expensive high R/inch insulation where it is thermally bridged by R1.2/inch wood is a waste. Save the high-R/inch foam budget for the exterior, where it's performance is at full measure, and not cut in half by the thermal bridging.
If foam cavity fill is favored, open cell + MemBrain will always beat partial fill closed cell on price/performance and a far greener option overall.
Mic and Jeremy,
Thank you for bringing your real-world experiences to this forum. As someone who installs sprayfoam for a living I hear similar comments from customers. Just this week I spoke to a client who reported that his normalized consumption was no greater in the house we insulated a couple of years ago than it had been in his old one, despite the new one being three times the size. Could these results have been achieved without sprayfoam? Of course, as Dana describes it above there are always options, but if you work with a good installer foam gets the job done quickly and efficiently in any kind of structure. If you are worried about the global warming potential of closed cell foam, you should look into some of the higher density water blown materials. I am in Ohio (climate zone 5) and we work extensively with a 1 pound density foam. At 3"+ we achieve a perm rating of 0.8 and R-15.
GBA readers,
Make your own decisions on these matters. But remember: code-minimum insulation levels are an excellent idea. Exceeding code minimums is even better.
Beware of spray foam installers who try to convince you that installing less than code-minimum R-values is OK.
Martin I'm not trying to suggest anyone use less than code minimum, just giving a real world opinion of closed cell foam based on 2 years of living in a closed cell home. It seems to be a lot of negative views of closed cell foam on this site with some continuing to say that thermal bridging kills its benefit. Given the efficiency of our home for the size and lack of complexity in the wall and roof design I just keep scratching my head at all of the talk of expensive double wall systems and extravagant roof designs to save very few dollars.
If I read the code correctly for zone 5 I need an R49 ceiling and R20 wall. My home meets the R20 requirement for walls but misses the R49 requirement by about 15 or so since we have 2x6 rafters with closed cell. To me when looking at the numbers it did not make sense to spend more money on roof insulation. The payback just did not seem to be there and right now my numbers have justified that decision. I've posted some details on the home in another thread about air sealing but for those who missed it here are the details.
Zone 5, NW Missouri
3750 sq/ft 1st floor + 2nd floor
1000 sq/ft finished basement
2x4 walls with closed cell spray foam and certainteed insulated vinyl siding.
2x6 rafters with closed cell spray foam
Lots of windows, Anderson 400 series mostly double hung with a some fixed
27' ceiling in great room, 10 ft ceilings.
Just under 52,000 cu/ft of conditioned volume with the finished basement included.
very complex roof line with 5 dormers plus a couple of bumpouts (pictures of front and back to show complexity of the exterior)
With spray foam I was able to seal the home very well even with all of the dormers and bumpouts. It was done quickly and easily without the addition of double walls, exterior foam, or any other extravagant building processes. Just traditional 2x4 wall framing and 2x6 rafters. My current home is more energy efficient for heating than my old 2,000 sq/ft home with a volume of 16,000 cu/ft. In fact with our house temp during the winter at 71 degrees, my energy use for heating with a combination of foam and geothermal is very close to passive house standards and exceeds it if you include the basement. That is without using the fireplace for heat. End of my rant. I'll continue to enjoy our home with spray foam and all of its downfalls.
Jeremy,
I'm not buying it.....post actual data, HDD, costs etc. There is no way your home is performing at PH standards. Study after study, with hard evidence to back it up disproves many of your statements.
Roughly 1.4Kwh per sq/ft per year correct? Im talking about heat.
We seem to have missed his attic insulation and planned furnace in the attic. 3 inches of foam in the attic will also have major thermal bridging and is far below code R value requirements.
BTW is there a permit for these upgrades?
Brad can you please enlighten me on my other "many statements" that you seem to infer I am not being truthful about?
Here is my usage for the past 12 months. I've added totals above the bar graph printed from my utility report. We have a baseline usage per day of about 62Kwh without air or heat. My totals from April 2015 through March 2016 was 28493 Kwh. Subtract my baseline usage of 22,630 and my total Kwh for air and heat is 5863 Kwh for the last 12 months.
HDD days from the last 12 months = 4683
CDD days from the last 12 months = 1419
Again Brad please let me know what "many statements" you are referring to. I'll be glad to try to correct my statements if I have stated something in error.
Jeremy
With a 62 kWh per day baseline electrical load contributing 211,000 BTUs of heat, it's not surprising that the heating system doesn't need to work that hard ;)
But lest we get into the weeds here, all camps make some good points. But to say "R-value is R-value, period" and hand-wave away the need for airtightness with some perfunctory statements like, "well, just air seal and detail your building envelope properly" is unrealistic and disingenuous in the real world, especially for a major recommended usage: attic floor insulation! Insulation piled deep on the attic floor is outside of the building envelope and exposed to outside temperatures, air currents, wind-washing, moisture, etc. Fiber insulation with air barriers on all six sides it ain't. And yet it's still continuously recommended, despite the acknowledgement that fiber insulation needs air barriers to function properly, and that attic insulation won't have them except on one side, not all six.
I have an R-50+ attic floor on paper, with a combination of mineral wool, cellulose, and fiberglass in multiple layers. In the real world, the cooling performance has been extremely disappointing (heating performance is what I expect), and last summer I spent more $ per cooling degree-day than I did the previous summer with only R-20 attic floor. This is documented. Probably I will this summer as well; I plan to measure and document it again. When I bring this kind of information up here I am generally assailed with reasons why what I report cannot be true because it violates the laws of physics, and insinuations that I'm an idiot who doesn't know how to read an infrared thermometer. When I press on, I get grudging acknowledgment from some of the more open-minded folks here that yes, air movement can be a problem for attic floor insulation in certain situations, that radiant heat blocking performance might be worse than the rated R-value indicates, that reduced nighttime cooling in a high-diurnal-temperature-range climate may be noticeable, etc. These are big deals! But they're rarely if ever brought up without pulling some teeth.
Nate we have two 60 gal water heaters and both a chest freezer and upright freezer outside of the conditioned space (garage and utility room) along with all of our outside and accent lighting so not all is contributing to our heat load.
Mic sorry for hijacking your thread, it was not my intention. My only intention was to post my experience with closed cell. I did not expect to be called a liar. I'll bow out now and hopefully you can get some continued help with your questions.
Jeremy,
I, for one, am not calling you a liar. Congratulations on your low energy bills.
Your energy bills are quite low (although not quite as low as those of a Passivhaus, according to my calculations). If you used 6,863 kWh to heat your house in one year, and your house measures 441 square meters, that's 15.56 kWh/square meter -- a little bit over the Passivhaus target of 15 kWh per square meter.
There are a few wrinkles, though: one is that the Passivhaus criteria calculate area differently than Americans, so your heating budget was higher per square meter than my calculation implies. Another wrinkle is that the 5862 kWh of electricity you used for heating wasn't the amount of heat that your building needed -- it was electricity, not heating energy. Assuming a COP of 3.0, the heating energy was 46.7 kWh per square meter.
Finally, the Passivhas standard requires that the total primary energy (source energy for electricity and etc.) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year. In your case, your house used 28,493 kWh for the year, or 64.6 kWh site energy per square meter. Assuming a source-to-site ratio of 3.34, that means that your house used 215.7 kWh per square meter of source energy, quite a bit more than the 120 kWh per square meter target.
I invite certified Passivhaus consultants to inform me if my calculations are wrong.
All that said, I'm not calling you a liar, by any means. Your house performs well, and everyone involved -- the designer, the builder, and you -- deserve congratulations.
Concerning air leakage through cellulose-insulated attics: You're right that many U.S. homes have leaky ceilings. But I don't think that you can fault GBA, since our site has been beating the drum in favor of air sealing since the day we began publication.
Concerning cost-effectiveness: It's certainly true that anyone who chooses to install spray foam insulation will find it hard to justify an R-49 roof assembly. Spray foam insulation is so expensive that the last R-15 is hard to justify, as you accurately report. Homeowners who install cellulose insulation, however (a much more affordable choice) will find it much easier to justify the expense of R-49 insulation than homeowners who choose to install spray foam.
Mic,
Concerning your furnace comments, you say that you would prefer a modulating furnace. As far as I am aware, the smallest modulating furnace offered by any mainstream U.S. manufacturer is 60K btu/hr and has a minimum modulation of 40%. That is great if your design heat load approaches 60K. However, if your heat load is less than 24K, it will perform like a single stage 24K furnace most of the time. Some of the manufacturers offer 2 stage furnaces at 40k capacity with a first stage of 70%. That would operate like a 28K single stage for cheaper than the 60K modulating furnace.
As a Canadian, you should look into the Chinook furnaces from Dettson. They offer modulating furnaces as small as 15K. I considered one of these for my home in Michigan, but decided that having something my local contractors could easily service was too important. (I find it ironic that the only company that seems to be offering small furnaces is mostly serving a cold climate.)
Martin I was not referring to you in my post. I have a lot of respect for your posts and expertise and in fact think your idea of what I think you call a "pretty good house" makes a lot more sense than trying to meet passive house standards. Also in my prior post it was my not my intention to state that our home meets passive house standards overall. My statement was very specific in talking about my energy use for heating. I had not looked at the standard for primary energy use and had no reason to. With a house of 5 that is lit up like a Christmas tree most of the time, two water heaters, and two extra deep freeze appliances, and a washer/dryer that never stops there is no way it would ever meet PH primary energy use standards. However in regards to heating and cooling, with a southwest facing envelope, it comes very close or meets PH standards for heating and cooling if I cheat a little and add my basement sq/footage. I say cheat because our basement maintains about 67 degrees year round without conditioning. It takes very little energy use. Since you did check my numbers for me I took a look at them and am coming up with something slightly different. Here are my calcs and please correct me where I am mistaken. In fairness it was a milder winter than normal, however I don't think my numbers would change drastically from this year to next.
Total sq meters 1st & 2nd floor = 348
Total sq meters basement = 93
Basement 60% rule = 56
Total calculated sq meters = 404
HVAC energy use = 5863/404 = 14.512 per sq/meter
Jeremy,
That's kWh of electricity, not kWh of heat energy. Converting your 14.5 kWh of electricity to heat energy (assuming a COP of 3.0), the result is 43.5 kWh/m2*year.
Assuming a COP of 4.0, the result is 58 kWh/m2*year.
Comparing the performance of an old 2000' house of unknown construction and air leakage to a new 3750' house is silly.
Comparing it to a NEW code min 2000' house with code-max 3ACH/50 air tightness would be more relevant, but still not completely. Larger houses have less exterior surface area per square foot of conditioned space than smaller houses. Comparing the volume of the houses is also an irrelevant metric (except when comparing blower door test numbers.) Heat loss is a function of exterior surface area, not volume. Performance standards at different subsidy levels in some programs in my area rightly use leakage per square foot of exterior surface at 50 pascals, not ACH/50.
There are many ways to air seal a house. Expanding foam insulation helps, but it doesn't seal the air leak between the bottom plate of the studs or between doubled up top plates etc. There are many ICF houses that should be inherently air tight (the walls CERTAINLY are) that test at 5ACH/50 or higher.
With the high number of bump outs corners and dormers in Jeremy's house air sealing with spray foam took a lot of detailing labor out of it, trading labor against a high cost insulation.
Open cell foam air seals at least as well as closed cell foam.
Thermal performance gained by the modestly higher R/inch of 0.7lb or 1.0lb water blown foam between thermally bridging framing is hard to rationalize against the higher cost. The 1lb foams are nearly 2x the polymer per R. It has a more favorable vapor permeance at ~R16 in a 2x4 cavity than 2lb foam though, but isn't as useful as a (much cheaper) smart vapor retarder solution.
Thank you Martin
Martin is right, PassiveHouse counts only site used kwh energy, not what's leveraged by heat pumps between the meter and the load.
They only advantage in PassiveHouse terms you get from heat pumps is for the reduced source-energy carbon. (But PassiveHouse methods of carbon accounting are so crudely apportioned and so seldom updated as to be nearly meaningless IMHO.) PassiveHouse doesn't even credit net-metered solar on the house unless it's at Net Zero.
Dana you wrote "With the high number of bump outs corners and dormers in Jeremy's house air sealing with spray foam took a lot of detailing labor out of it, trading labor against a high cost insulation."
This is my entire point about spray foam. It is fast and much easier to get good air sealing results. Even with the complexity of our home and number of doors/windows we blower door tested at 1.9Ach50. After my latest air sealing efforts in the garage to prevent duct leakage into the conditioned space my guess is we are probably at 1.5 or less given the amount of leakage I had. My cost for closed cell in 2013 was .85 per sq/ft per inch of foam.
There is R49 on paper and there is R49 in application. I have no doubt if you were the homeowner having a house built using your alternative methods of insulation, your home would be extremely well performing. In reality most homeowners are not as involved or detailed as we may be. Most builders in our area are building multiple houses at a time and attention to detail, especially in regards to air sealing and insulation is not one of there strong points. As long as the exterior looks good the house sells and the homeowner rarely is around to see what's underneath the pretty stuff. A friend of mine had his home built at the same time as ours. 3,200 sq/ft single level ranch with 8' ceilings. 2x6 walls and batt insulation all done by the contractor. When I visit in the winter they are all sitting in sweatshirts with the heat at 68 degrees because their heating bills are so high. They were shocked when I showed them a comparison of what I was using.
Jeremy: Code max is 3ACH/50. Any house that meets that would get the performance out of any type of insulation. Any house that DOESN'T meet that is substandard, and a code violation.
Unless your friend's house actually meets code and is heating with a comparable heat pumps the size of their heating bills relative to yours isn't a good measure of anything. Also the fact that it's a 3200' single story already makes his an inefficient building shape relative to most 2-story homes. The ways this is NOT an apples-to-apples comparisons of the insulation type are significant. What is your friend's ACH/50 number?
A 1.9 ACH/50 is decent, but also fairly easy to hit using just about any air sealing method. With a messy framing design like yours air sealing the cavities with foam makes that easier. But the foam on it's own is neither sufficient nor necessary.
Dana I get it. You don't like foam. Go out in the real world and compare houses to houses with the same r-value using foam or alternative methods. Not houses that are high end built by energy conscious builders because this makes up few of the houses out there. Compare your average builders who are building in mass. The house that used foam will outperform almost every time.
Jeremy,
I'm sure neither Brad nor any one else considers you a liar. The disagreement is over the building science, and if people express doubts it is because they worry that if your house performs in a way that goes against what they understand about insulation, we just lost a lot of what we considered settled facts about R value and air sealing.
As a designer, with a quite tenuous grasp of most of the numbers involved, I'd prefer to spend some time in your outdoor covered patio. It looks like a nice place to hang out.
That's just it, really. This site is an amazing resource for how to do things "right." But "right" is often expensive and infrequent and unrealistic in the real world. When you actually get out there and try to build or renovate something, you run into endless problems: nobody's heard of dense-packed cellulose or has confidence that it works; you can't get a conventional furnace rated below 40,000 BTUs; code officials demanding 6 mil poly everywhere; incredible resistance to installing ducts, furnaces, or water heaters anywhere but the attic or garage; ants and termites really like foam, especially moist underground foam. Etc. The difference between the impeccably-designed, scrupulously-detailed masterpieces showcased on this site and the poor quality of most U.S. housing stock and construction conventions is simply stunning.
I think the point is that spray foam does a lot of jobs and does them pretty well, with a minimum level of understanding and knowledge of building science on the part of the applicators. Maybe in an ideal world more tradesmen and GCs would have masters degrees in building science and would be able to design and build a wall on the fly with perfectly ordered and detailed control layers, but we don't live in that world and honestly we probably never will.
Nate,
I agree with most of your points.
Although GBA often showcases Passivhaus buildings, my own preference is for the "pretty good house." Figuring out what a pretty good house means is up to the builder and the homeowner, and the answer will vary depending on your climate zone.
Concerning the difficulties that homeowners have in locating conscientious builders: this is a real problem. In some areas of the country, it's easier to find energy-conscious builders than in other areas.
As the home building industry makes its slow transition from fast-and-crappy to high-performance, GBA has a role to play: we want to highlight best practices, holding these practices up to our industry in hopes that these models will help nudge the industry in the right direction.
Jeremy: "Dana I get it. You don't like foam. Go out in the real world and compare houses to houses with the same r-value using foam or alternative methods."
Out here in the real world I've done just that, in multiple ways. The premium paid for 2lb foam over half pound foam just isn't buying much, and can create problematic less moisture resilient stack-ups. Homes insulated with cellulose run about as tight in blower door tests as houses with half-pound foam, and have about the same energy use performance even without extra air sealing detailing. Sometimes when bid as half-pound foam it comes in cheaper than with cellulose.
The perception that I "...don't like foam" is simply not the case- I've used it in my own house. A more accurate reading would be that I don't like spending more money and taking a higher environmental hit when it doesn't buy anything. The difference in whole-wall performance between 2x6 with 5.5" of half pound foam and 5" of 2lb foam can be made up at lower installed cost and at lower environmental impact with 3/8" fan-fold XPS siding underlayment.
Save the 2lb foam budget for where it's low vapor permeance & high R/inch properties are actually buying something, such as foundation walls. Between wall or roof framing it's pretty much wasted. There's an argument for some amounts of 2lb foam in some unvented roof assemblies, but in new construction it's still usually cheaper to go with rigid foam above the roof deck with open cell under the roof deck. But with roof lines as cut up as yours that might not be the case. Still, in a zone 5 climate it's both cheaper and better to go with 3" of closed cell on the roof deck, with 8" of open cell below that to hit R49-ish, for both better drying rate and less thermal bridging, not to mention lower cost. That neatly fits into a standard 2x12 milled rafter, and can be safely done in four lifts (two closed cell, two open cell).
If you've read many of my discussions about unvented roof assemblies on this forum you would find MANY instances where I've recommended 2lb foam under the roof deck sufficient for dew point control with either fiber or open cell foam below that, and many many instances of recommending rigid foam sheathing on both walls and roofs. That should be sufficient evidence contrary to the notion that I "...don't like foam". I like foam well enough when appropriately applied. The mere fact that I'm not a foam-chauvinist doesn't mean I don't like foam. Just because a hammer is the perfect tool for some applications doesn't mean it's the only tool, or the best tool that can/should be applied universally. Sprayed polyurethane foam has no special performance or other high ground to stand on, despite it's often useful properties.