Good news, I got clearance from my wife to start designing a house for us. Turns out that designing a house is hard, especially since all my work is commercial or govt. We want to do a highly insulated, low cost, modern home. Not necessarily passive house level, but certainly far better than code.
Can anyone recommend a good source for passive house type wall assemblies?
Thanks
tduds
Aug 2, 18 2:01 pm
inb4 "Hire an Architect"
http://www.phius.org/phius-cer... has some basic data for certified PassiveHaus projects. I think if you get PHIUS certified you get access to construction details, which is a pretty invaluable resource.
It might be worth pursuing certification, just to get a knowledge baseline for your own future. Otherwise I'd suggest looking up a local consultant and taking them out for drinks.
https://www.sips.org/ I believe also has some assembly details. Obviously SIPs are pretty restrictive, but with single family construction it's not too hard to start with a simple geometry that can accommodate SIP construction.
Good luck! I'm hoping to live that dream in 5-10 years.
randomised
Aug 2, 18 3:04 pm
Consulting starts at ... an hour!
just kidding
It all depends on the climate and local conditions, will it be freestanding, can you organise the house with the path of the sun, etc. it might require some math though...
Miles Jaffe
Aug 2, 18 4:21 pm
Fotget SIPS: too expensive, hard to mech, not particularly flexible. Climate dictates insulation. Tight is good but too tight is bad. Control solar exposure, you can passively heat and cool (or assist) with thermal mass, overhangs, and ventilation.
As awful as it is, closed cell spray foam pretty much eliminates infiltration - which is by far the biggest source of loss.
#1 cost control is size. Keep it small to keep it cheap. Master plan the site and think build-out over time.
Coming from residential the biggest lesson on the first highrise was scale. You may have a similar lesson in the opposite direction.
Keep it simple, resist the urge to upgrade all the materials. Stick to a simple palette, sweat every detail and spend a bit more on a single focus feature (kitchen, stair, whatever) that will serve to bring the whole project up.
Ask a res arch you respect to crit your design. A builder, too. Listen carefully.
wurdan freo
Aug 2, 18 4:39 pm
you think it's hard now... wait until your first review with the client... you'll be living... in a van down by the river :)
Keep reading until you're confused or fall asleep.
tduds
Aug 6, 18 12:25 pm
Lstiburek is my homeboy.
Wood Guy
Aug 2, 18 5:58 pm
Shellarchitect, there are lots of wall assembly details available at greenbuildingadvisor.com, and foursevenfive.com has several good assemblies. JLC and FHB regularly show creative new assemblies. Building Science Corp has some new ones as well.
This forum is also a good place to discuss the topic. What are your criteria? My go-to is double stud with cellulose, with caveats, but I've used a lot of different assemblies for different situations.
shellarchitect
Aug 3, 18 5:25 pm
What r value do you shoot for in the walls and roof? I was thinking 2x8'
with exterior rigid ins....
Wood Guy
Aug 4, 18 9:51 am
It depends on the situation. For walls, with double studs and cellulose, at least R-40, because once you're building two walls, spacing them farther apart doesn't cost much extra. The lowest cost way to get reasonably high performance is 2x6 walls (with any fibrous insulation) and, in zone 6, 2" of polyiso on the outside of the sheathing. I've been thinking a lot about 2x8 walls as well; their whole-wall R-value is in the mid-20's, which isn't bad. If you add exterior insulation, though, be very careful about the proportion of R-value of interior to exterior, so you don't end up with a dewpoint problem. The building code has some potentially dangerous, confusing language when it comes to dewpoint control.
In roofs, for new construction in zone 6 I like R-60 loose-blown cellulose, but again it depends on the situation. In a cathedral ceiling the cost to go above code-minimum R-49 has quickly diminishing returns.
Wood Guy
Aug 4, 18 9:58 am
There is absolutely no reason to resort to spray foam in new construction. The easiest way to control infiltration is by identifying the airtight layer and keeping it continuous around the building; I've found that taping the sheathing is an easy way to get extremely low infiltration numbers. (We've had as low as 0.12 ACH50 on my projects using that method--5X lower than the Passive House standard.) There are various ways to handle airtightness at the ceiling plane, depending on several factors.
Miles Jaffe
Aug 4, 18 10:14 am
What tape on which sheathing? Some of those boards are just as bad as spray foam.
Wood Guy
Aug 4, 18 12:18 pm
Miles, we're just finishing one now that has CDX sheathing with 3M 8067 All Weather Flashing Tape on the walls, Pro Clima Intello on the ceiling, that's the one that air tested at 0.12 ACH50. I've done several with Zip sheathing and Zip tape. One is about to start that will have Zip sheathing and their liquid flashing.
At my former place of employment we had trouble with conventional OSB, couldn't get below 1.0 ACH50, but once we switched to Zip sheathing we routinely got below 0.4 ACH50.
I've used Henry Blueskin self-adhered WRB on a couple of projects with good results, but it's not usually necessary.
My first project with Huber's Zip-R sheathing is about to start. It has polyiso foam adhered to one side. The pentane-based blowing agents in polyiso are relatively benign, compared to those in XPS or closed cell spray foam.
Very few building materials have the negative environmental impact of conventional closed cell spray foam. The new type with the HFO blowing agent is much less bad, but still orders of magnitude worse than cellulose or mineral wool.
won and done williams
Aug 2, 18 6:42 pm
Unless technical detailing is really your thing, I'd choose a simple system that most any decent contractor can construct. If you come up with something too complex, your pool of contractors will dry up fast, and you'll spend far more on a complex enclosure system than you would on other parts of the project - the parts your wife will care about.
I would look at this as an opportunity to design to your unique lifestyle. I've looked at countless old and beautiful houses, but very few, if any, match what I would like for my family at this point in our lives. You have a rare opportunity. Take advantage of it.
mightyaa
Aug 2, 18 8:14 pm
"Good news, I got clearance from my wife to start designing a house for us"
Poor guy. Been there, done that, nearly killed the marriage, and bought something else. The hardest part isn't the details, it is reigning in the design to fit within your budget and getting that to align with your spouse's (and your own) expectations of all those glossy pictures you've probably been showing them over the years and those stacks of architectural magazines to corrupt their (and your) idea of "acceptable". Quality comes with a price tag.
As others have said; KISS (Keep it simple & stupid). You'll get better pricing. For my walls, I'd do a simple 2x6 with batt, and add a continuous insulation barrier over the sheathing with a rain barrier type cladding (my preference is real stone slats, my budget is probably higher end fiber cement or wood). Real masonry or stone with a real air cavity still works fantastic.
Roofs have become a major pain lately in forensics. Keep it reasonably simple as well and make sure you ventilate OR ensure you have a bombproof, uninterrupted vapor barrier system (no recessed lights, speakers, etc. Don't install the ceiling gyp to the bottom of roof joist directly, but instead use a hat channel to provide something of an air break.
Oh... and don't put a deck over occupied space unless you really know what you are doing. I'm tired of looking at rotting things.
shellarchitect
Aug 6, 18 9:44 am
Can you expand on the hat channel between the gyp and bottom chord of the truss joist? I've never really understood why is sometimes included or not included.
shellarchitect
Aug 3, 18 5:28 pm
Looks like the land that I wanted but thought was overpriced has sold after just a couple weeks on the market, may have to adjust my expectations, stupid economy....
wurdan freo
Aug 3, 18 7:43 pm
yeah good luck... I've been looking at 1000 sf hovels that are listed at 400k... pretty depressing...
JLC-1
Aug 3, 18 11:48 pm
Let me guess, denver....
wurdan freo
Aug 4, 18 3:33 am
Ding ding ding
shellarchitect
Aug 4, 18 10:21 am
Teardowns?
JLC-1
Aug 6, 18 10:15 am
I lived for 6 years in a 1969 single wide on a 2500 sq.ft. lot for which I paid 230K - built a bedroom and bath and sold it for 300K. trailer park 15 minutes from aspen. frozen pipes in december. If you can afford to tear it down, that's the move, but most of the time you are better off remodeling, even if you keep just a wall from the existing; easier on the permit.
J G
Nov 21, 23 6:51 pm
I'd love to know how this comment aged to now in 2023
shellarchitect
Aug 4, 18 1:23 pm
Great info here. If no one minds I'll prob be asking a lot of questions as my design progresses
shellarchitect
Aug 6, 18 9:51 am
Reading a lot about various green certifications.... Is there any particular value to one over another? LEED vs Passive vs Energy Star vs HERS....
I'm leed accredited, but have never used it for anything.
Wood Guy
Aug 6, 18 3:09 pm
The Pretty Good House concept is the most practical. If you feel like you've met the requirements, you can buy yourself a plaque.
Passive House drives the energy-efficient construction movement, and going through the process will probably add the most value to your resume and skill set, but it rarely makes financial sense for single-family homes.
If your state provides incentives, it can make sense to go for Energy Star (including specific HERS ratings, as I understand it; it's not a thing in my state).
IMO it's a terrible time to buy. When overpriced property is snapped up immediately it's a sure sign that the top is here and the crash is coming.
It's all cyclic, be patient.
shellarchitect
Aug 6, 18 3:27 pm
I plan on selling my current home at an equally or hopefully more inflated value (greater fool theory)
whistler
Aug 8, 18 4:42 pm
Just insulate the shit out of the walls/foundation/roof and seal everything with Sigatape, good to go! That is the coles notes version but not far off either!
I've found that spray foam is pretty cheap as a material on its own. You just have to buy the equipment and do it yourself. It's really easy to mess up and not let the stuff expand and harden properly if you don't provide time between your layers or overspray a layer too thick. Since we can always sell the idea of "occupied" window nooks, we build a lot out of 24"-30" thick walls, 2x4 construction. We don't even talk about R-value in house or with the client. Clients usually rent the spray foam equipment and I show them how to use it. They do a way better job themselves than cheap labor, since they care. On the inside wall we cheat a lot by doing the 2x4s on the flat at 3' O.C. and 5/8" 4x9 sheet rock. A lot of clients decide to rock the walls themselves as well, so giving them 3.5" to work with is easier. Once the insulation is in and all the trim goes up, wainscot, chair rail, etc, it doesn't seem that flimsy. The electricians like working in the wall (skinny guys) and they don't have to drill holes since they install directly to the back side of the 2x4s. 2x4 blocking is attached where we want outlet/switch boxes. We just have the framer keep all drops in a pile and the electrician uses them up as needed. We almost always keep plumbing out of the exterior walls.
Miles Jaffe
Aug 14, 18 12:46 pm
I'm enjoying the fantasy vision of client John Dough spending a week blowing foam and stapling up fiberglass batts to save $800, then getting into his GL 550 and driving back to the city.
joseffischer
Aug 14, 18 1:21 pm
Different clients I suppose ; P... also, if you can get me a crew that charges only $800 for 2 feet plus of spray foam insulation, give me their number please. Now that I'm at an architecture firm I don't do much of this work anymore, but at the time, most of my clients were fellow Georgia Tech grads. Since they went comp science and engineering, they typically have a lot more spending power to upgrade their homes than I did, but they loved being hands-on, and it actually smoothed over jobs to give them a trade to deal with rather than have them randomly show up after their work day and nick-pick everything.
Non Sequitur
Aug 14, 18 1:26 pm
You spec up to 24" thick of spray-foam?
joseffischer
Aug 14, 18 5:30 pm
As a remodeler we built with 24" thick of spray-foam. My architectural "education" was only used to get residential permits at the time. The stuff was insanely cheap. As an architect at a corporate firm, I've never spec'd anything but iso-board on exterior, batt inside, for walls.
I've been in a lot of buildings that got spray foam in crawlspaces between joists where rats would dig tunnels in the stuff. I've not heard back yet on any clients complaining about hearing noises in the walls, but that was one concern I had about the practice.
joseffischer
Aug 14, 18 5:36 pm
I've only had 2 chances to work on previous projects I had built. Both times we opened up the walls to add a wing and found dry construction and foam intact. I don't know what would happen with a good leak, from above for example, where an old roof is pouring water into the wall system. I'd assume the wood studs would rot to non-existence. Most of the work I did is only 6-10 years old, so I can't say that the systems have "stood the test of time" yet...
joseffischer
Aug 14, 18 5:58 pm
So I haven't done a full check since I haven't had this on a project yet, but a google search talks about maximum foam thickness mostly related to E84 flame spread testing, so as a specced product, I would have to limit the thickness based on that. Interestingly, many manufacturer thickness limits result in a system that on its own does not provide enough R-value for northern climates.
Miles Jaffe
Aug 16, 18 8:37 am
2" of foam is environmentally unsound. 2' deserves a Darwin Award.
Non Sequitur
Aug 16, 18 9:23 am
Our office has almost eliminated spray-foam from our detail library... only the fresh grads still think it's a magical cure-all product. I'd like to see how 24" of foam reacts to a spark.
https://database.passivehouse.... is the assembly database, I think. When I took a PassiveHouse course our instructor recommended that and checking out the details on the 475 website.
He has a lot of spray foam horror stories...
shellarchitect
Aug 19, 18 8:55 am
I have looked but have not selected a system yet. I really like 475 too, thanks
found this over the weekend, calls the winner out of 17 different wall systems to be a 2x6 staggered stud wall w/ blown in fiberglass and 1" XPS...
Thoughts from those way more knowledgeable than me?
Miles Jaffe
Aug 20, 18 6:16 pm
I've opened up a few blown-in jobs years later and invariably founding considerable settling that left portions of the wall insulated. Attic / ceiling use is fine, but I wouldn't use it in walls.
shellarchitect
Aug 20, 18 9:36 pm
Fiberglass or cellulose, or both?
Miles Jaffe
Aug 20, 18 10:07 pm
Cellulose mostly. The harder you pack it the less it settles but packing reduces R value. I prefer mineral wool - better performance all around, easier to get a good installation. Well worth the increased material cost.
Wood Guy
Aug 21, 18 10:37 am
Miles, packing doesn't reduce the R-value by much. At most it's about R-3.8/in, but the tightest packs (about 4.25 pcf) are still R-3.55/in. There is no way it can settle if properly installed over 3.5 pcf (loose density is 1.8 pcf) unless it gets saturated, but both problems (poor installation and saturation) can certainly happen, especially in retrofit situations. Mineral wool is great too.
senjohnblutarsky
Aug 21, 18 10:47 am
Mineral wool is great, but damn it's expensive. I wanted to go that route, but just couldn't justify the expense.
alex2
Nov 18, 23 6:23 pm
In scanning the walls with blown-in cellulose i frequently see significant insulated areas due to settlement much prefer mineral wool bats with 2x8 construction.
alex2
Nov 14, 18 1:31 am
I've been designing and writing about energy efficient house for almost 50 years. My earlier houses were timber frame with SIPS panels. As prices rose, I have switched to more conventional framing techniques. The latest energy code requires full exterior foam encapsulation so I use the insulated Zipwall sheathing/tape system on the exterior. I now specify 2 x 8 stud walls with mineral wool batt insulation and Certainteed's special breathable vapor barrier. With this assembly it is very easy to get R-40 at reasonable cost. For the roof, In use either exposed timbers or trusses at four feet on center. with 6" of recycled form for insulation. Air to air heat exchangers are vital for tight houses. Panasonic makes some dandy ones reasonable priced ones. Finally, i recommend insulates slab on grade with radiant heat.
Non Sequitur
Nov 14, 18 7:36 am
Curious as to why you need to specify a high perm vapour barrier. What is the CT product name?
alex2
Nov 15, 18 12:06 am
m
Donna Sink
Nov 14, 18 7:51 am
Posting just to keep tabs on this conversation. About to start a tight remodel project and look forward to all the resources you guys have shared.
alex2
Nov 15, 18 12:14 am
Membrain is a variable perm vapor barrier, not high perm. Code officials require a vapor barrier for unfaced insulation. The barrier has to be in place for your blower door test. The newest code raises lots of issues. Tried to reply to Non Sequitur but site froze.
Non Sequitur
Nov 15, 18 8:00 am
Thanks Alex. The reply feature is wonky. I’ve looked up this membrain and although the name is dumb, it’s an interesting idea. We typically specify permeable AB on the exterior when we expect high moisture buildup inside the wall assemblies but never have we installed AB on the inside. I’d be worried that it can be easily compromised by drywall screws and various wall hooks which would funnel any moisture to those penetrations.
Good news, I got clearance from my wife to start designing a house for us. Turns out that designing a house is hard, especially since all my work is commercial or govt. We want to do a highly insulated, low cost, modern home. Not necessarily passive house level, but certainly far better than code.
Can anyone recommend a good source for passive house type wall assemblies?
Thanks
inb4 "Hire an Architect"
http://www.phius.org/phius-cer... has some basic data for certified PassiveHaus projects. I think if you get PHIUS certified you get access to construction details, which is a pretty invaluable resource.
It might be worth pursuing certification, just to get a knowledge baseline for your own future. Otherwise I'd suggest looking up a local consultant and taking them out for drinks.
https://www.sips.org/ I believe also has some assembly details. Obviously SIPs are pretty restrictive, but with single family construction it's not too hard to start with a simple geometry that can accommodate SIP construction.
Good luck! I'm hoping to live that dream in 5-10 years.
Consulting starts at ... an hour!
just kidding
It all depends on the climate and local conditions, will it be freestanding, can you organise the house with the path of the sun, etc. it might require some math though...
Fotget SIPS: too expensive, hard to mech, not particularly flexible. Climate dictates insulation. Tight is good but too tight is bad. Control solar exposure, you can passively heat and cool (or assist) with thermal mass, overhangs, and ventilation.
As awful as it is, closed cell spray foam pretty much eliminates infiltration - which is by far the biggest source of loss.
#1 cost control is size. Keep it small to keep it cheap. Master plan the site and think build-out over time.
Coming from residential the biggest lesson on the first highrise was scale. You may have a similar lesson in the opposite direction.
Keep it simple, resist the urge to upgrade all the materials. Stick to a simple palette, sweat every detail and spend a bit more on a single focus feature (kitchen, stair, whatever) that will serve to bring the whole project up.
Ask a res arch you respect to crit your design. A builder, too. Listen carefully.
you think it's hard now... wait until your first review with the client... you'll be living... in a van down by the river :)
https://youtu.be/bXk3teJpzGU
https://buildingscience.com/do...
Keep reading until you're confused or fall asleep.
Lstiburek is my homeboy.
Shellarchitect, there are lots of wall assembly details available at greenbuildingadvisor.com, and foursevenfive.com has several good assemblies. JLC and FHB regularly show creative new assemblies. Building Science Corp has some new ones as well.
This forum is also a good place to discuss the topic. What are your criteria? My go-to is double stud with cellulose, with caveats, but I've used a lot of different assemblies for different situations.
What r value do you shoot for in the walls and roof? I was thinking 2x8'
with exterior rigid ins....
It depends on the situation. For walls, with double studs and cellulose, at least R-40, because once you're building two walls, spacing them farther apart doesn't cost much extra. The lowest cost way to get reasonably high performance is 2x6 walls (with any fibrous insulation) and, in zone 6, 2" of polyiso on the outside of the sheathing. I've been thinking a lot about 2x8 walls as well; their whole-wall R-value is in the mid-20's, which isn't bad. If you add exterior insulation, though, be very careful about the proportion of R-value of interior to exterior, so you don't end up with a dewpoint problem. The building code has some potentially dangerous, confusing language when it comes to dewpoint control.
In roofs, for new construction in zone 6 I like R-60 loose-blown cellulose, but again it depends on the situation. In a cathedral ceiling the cost to go above code-minimum R-49 has quickly diminishing returns.
There is absolutely no reason to resort to spray foam in new construction. The easiest way to control infiltration is by identifying the airtight layer and keeping it continuous around the building; I've found that taping the sheathing is an easy way to get extremely low infiltration numbers. (We've had as low as 0.12 ACH50 on my projects using that method--5X lower than the Passive House standard.) There are various ways to handle airtightness at the ceiling plane, depending on several factors.
What tape on which sheathing? Some of those boards are just as bad as spray foam.
Miles, we're just finishing one now that has CDX sheathing with 3M 8067 All Weather Flashing Tape on the walls, Pro Clima Intello on the ceiling, that's the one that air tested at 0.12 ACH50. I've done several with Zip sheathing and Zip tape. One is about to start that will have Zip sheathing and their liquid flashing.
At my former place of employment we had trouble with conventional OSB, couldn't get below 1.0 ACH50, but once we switched to Zip sheathing we routinely got below 0.4 ACH50.
I've used Henry Blueskin self-adhered WRB on a couple of projects with good results, but it's not usually necessary.
My first project with Huber's Zip-R sheathing is about to start. It has polyiso foam adhered to one side. The pentane-based blowing agents in polyiso are relatively benign, compared to those in XPS or closed cell spray foam.
Very few building materials have the negative environmental impact of conventional closed cell spray foam. The new type with the HFO blowing agent is much less bad, but still orders of magnitude worse than cellulose or mineral wool.
Unless technical detailing is really your thing, I'd choose a simple system that most any decent contractor can construct. If you come up with something too complex, your pool of contractors will dry up fast, and you'll spend far more on a complex enclosure system than you would on other parts of the project - the parts your wife will care about.
I would look at this as an opportunity to design to your unique lifestyle. I've looked at countless old and beautiful houses, but very few, if any, match what I would like for my family at this point in our lives. You have a rare opportunity. Take advantage of it.
"Good news, I got clearance from my wife to start designing a house for us"
Poor guy. Been there, done that, nearly killed the marriage, and bought something else. The hardest part isn't the details, it is reigning in the design to fit within your budget and getting that to align with your spouse's (and your own) expectations of all those glossy pictures you've probably been showing them over the years and those stacks of architectural magazines to corrupt their (and your) idea of "acceptable". Quality comes with a price tag.
As others have said; KISS (Keep it simple & stupid). You'll get better pricing. For my walls, I'd do a simple 2x6 with batt, and add a continuous insulation barrier over the sheathing with a rain barrier type cladding (my preference is real stone slats, my budget is probably higher end fiber cement or wood). Real masonry or stone with a real air cavity still works fantastic.
Roofs have become a major pain lately in forensics. Keep it reasonably simple as well and make sure you ventilate OR ensure you have a bombproof, uninterrupted vapor barrier system (no recessed lights, speakers, etc. Don't install the ceiling gyp to the bottom of roof joist directly, but instead use a hat channel to provide something of an air break.
Oh... and don't put a deck over occupied space unless you really know what you are doing. I'm tired of looking at rotting things.
Can you expand on the hat channel between the gyp and bottom chord of the truss joist? I've never really understood why is sometimes included or not included.
Looks like the land that I wanted but thought was overpriced has sold after just a couple weeks on the market, may have to adjust my expectations, stupid economy....
yeah good luck... I've been looking at 1000 sf hovels that are listed at 400k... pretty depressing...
Let me guess, denver....
Ding ding ding
Teardowns?
I lived for 6 years in a 1969 single wide on a 2500 sq.ft. lot for which I paid 230K - built a bedroom and bath and sold it for 300K. trailer park 15 minutes from aspen. frozen pipes in december. If you can afford to tear it down, that's the move, but most of the time you are better off remodeling, even if you keep just a wall from the existing; easier on the permit.
I'd love to know how this comment aged to now in 2023
Great info here. If no one minds I'll prob be asking a lot of questions as my design progresses
Reading a lot about various green certifications.... Is there any particular value to one over another? LEED vs Passive vs Energy Star vs HERS....
I'm leed accredited, but have never used it for anything.
The Pretty Good House concept is the most practical. If you feel like you've met the requirements, you can buy yourself a plaque.
Passive House drives the energy-efficient construction movement, and going through the process will probably add the most value to your resume and skill set, but it rarely makes financial sense for single-family homes.
If your state provides incentives, it can make sense to go for Energy Star (including specific HERS ratings, as I understand it; it's not a thing in my state).
(In case you don't know about the Pretty Good House movement, here's the blog post I wrote that introduced the concept: http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/pretty-good-house. GBA is going to be down on 8/7 while they set up a new site.)
great info, thanks
IMO it's a terrible time to buy. When overpriced property is snapped up immediately it's a sure sign that the top is here and the crash is coming.
It's all cyclic, be patient.
I plan on selling my current home at an equally or hopefully more inflated value (greater fool theory)
Just insulate the shit out of the walls/foundation/roof and seal everything with Sigatape, good to go! That is the coles notes version but not far off either!
A house without a mortegage.
I've found that spray foam is pretty cheap as a material on its own. You just have to buy the equipment and do it yourself. It's really easy to mess up and not let the stuff expand and harden properly if you don't provide time between your layers or overspray a layer too thick. Since we can always sell the idea of "occupied" window nooks, we build a lot out of 24"-30" thick walls, 2x4 construction. We don't even talk about R-value in house or with the client. Clients usually rent the spray foam equipment and I show them how to use it. They do a way better job themselves than cheap labor, since they care. On the inside wall we cheat a lot by doing the 2x4s on the flat at 3' O.C. and 5/8" 4x9 sheet rock. A lot of clients decide to rock the walls themselves as well, so giving them 3.5" to work with is easier. Once the insulation is in and all the trim goes up, wainscot, chair rail, etc, it doesn't seem that flimsy. The electricians like working in the wall (skinny guys) and they don't have to drill holes since they install directly to the back side of the 2x4s. 2x4 blocking is attached where we want outlet/switch boxes. We just have the framer keep all drops in a pile and the electrician uses them up as needed. We almost always keep plumbing out of the exterior walls.
I'm enjoying the fantasy vision of client John Dough spending a week blowing foam and stapling up fiberglass batts to save $800, then getting into his GL 550 and driving back to the city.
Different clients I suppose ; P... also, if you can get me a crew that charges only $800 for 2 feet plus of spray foam insulation, give me their number please. Now that I'm at an architecture firm I don't do much of this work anymore, but at the time, most of my clients were fellow Georgia Tech grads. Since they went comp science and engineering, they typically have a lot more spending power to upgrade their homes than I did, but they loved being hands-on, and it actually smoothed over jobs to give them a trade to deal with rather than have them randomly show up after their work day and nick-pick everything.
You spec up to 24" thick of spray-foam?
As a remodeler we built with 24" thick of spray-foam. My architectural "education" was only used to get residential permits at the time. The stuff was insanely cheap. As an architect at a corporate firm, I've never spec'd anything but iso-board on exterior, batt inside, for walls.
I've been in a lot of buildings that got spray foam in crawlspaces between joists where rats would dig tunnels in the stuff. I've not heard back yet on any clients complaining about hearing noises in the walls, but that was one concern I had about the practice.
I've only had 2 chances to work on previous projects I had built. Both times we opened up the walls to add a wing and found dry construction and foam intact. I don't know what would happen with a good leak, from above for example, where an old roof is pouring water into the wall system. I'd assume the wood studs would rot to non-existence. Most of the work I did is only 6-10 years old, so I can't say that the systems have "stood the test of time" yet...
So I haven't done a full check since I haven't had this on a project yet, but a google search talks about maximum foam thickness mostly related to E84 flame spread testing, so as a specced product, I would have to limit the thickness based on that. Interestingly, many manufacturer thickness limits result in a system that on its own does not provide enough R-value for northern climates.
2" of foam is environmentally unsound. 2' deserves a Darwin Award.
Our office has almost eliminated spray-foam from our detail library... only the fresh grads still think it's a magical cure-all product. I'd like to see how 24" of foam reacts to a spark.
A house without a mortgage.
@shellarchitect, Have you looked at https://passipedia.org/start yet?
https://database.passivehouse.... is the assembly database, I think. When I took a PassiveHouse course our instructor recommended that and checking out the details on the 475 website.
He has a lot of spray foam horror stories...
I have looked but have not selected a system yet. I really like 475 too, thanks
https://c.ymcdn.com/sites/www.nibs.org/resource/resmgr/BEST/BEST2_EE6-4.pdf
found this over the weekend, calls the winner out of 17 different wall systems to be a 2x6 staggered stud wall w/ blown in fiberglass and 1" XPS...
Thoughts from those way more knowledgeable than me?
I've opened up a few blown-in jobs years later and invariably founding considerable settling that left portions of the wall insulated. Attic / ceiling use is fine, but I wouldn't use it in walls.
Fiberglass or cellulose, or both?
Cellulose mostly. The harder you pack it the less it settles but packing reduces R value. I prefer mineral wool - better performance all around, easier to get a good installation. Well worth the increased material cost.
Miles, packing doesn't reduce the R-value by much. At most it's about R-3.8/in, but the tightest packs (about 4.25 pcf) are still R-3.55/in. There is no way it can settle if properly installed over 3.5 pcf (loose density is 1.8 pcf) unless it gets saturated, but both problems (poor installation and saturation) can certainly happen, especially in retrofit situations. Mineral wool is great too.
Mineral wool is great, but damn it's expensive. I wanted to go that route, but just couldn't justify the expense.
In scanning the walls with blown-in cellulose i frequently see significant insulated areas due to settlement much prefer mineral wool bats with 2x8 construction.
I've been designing and writing about energy efficient house for almost 50 years. My earlier houses were timber frame with SIPS panels. As prices rose, I have switched to more conventional framing techniques. The latest energy code requires full exterior foam encapsulation so I use the insulated Zipwall sheathing/tape system on the exterior. I now specify 2 x 8 stud walls with mineral wool batt insulation and Certainteed's special breathable vapor barrier. With this assembly it is very easy to get R-40 at reasonable cost. For the roof, In use either exposed timbers or trusses at four feet on center. with 6" of recycled form for insulation. Air to air heat exchangers are vital for tight houses. Panasonic makes some dandy ones reasonable priced ones. Finally, i recommend insulates slab on grade with radiant heat.
Curious as to why you need to specify a high perm vapour barrier. What is the CT product name?
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Posting just to keep tabs on this conversation. About to start a tight remodel project and look forward to all the resources you guys have shared.
Membrain is a variable perm vapor barrier, not high perm. Code officials require a vapor barrier for unfaced insulation. The barrier has to be in place for your blower door test. The newest code raises lots of issues. Tried to reply to Non Sequitur but site froze.
Thanks Alex. The reply feature is wonky. I’ve looked up this membrain and although the name is dumb, it’s an interesting idea. We typically specify permeable AB on the exterior when we expect high moisture buildup inside the wall assemblies but never have we installed AB on the inside. I’d be worried that it can be easily compromised by drywall screws and various wall hooks which would funnel any moisture to those penetrations.
I use variable permeance membranes on almost all of my projects. Certainteed Membrain is ok but the flimsiest of all the options. I spec Siga Majrex (https://performancebuildingtapes.com/product/siga-majrex-200-siga-tapes/) or Pro Clima Intello (https://475.supply/products/intello-plus). Both are extremely durable, though twice the cost of Membrain. All are based on the same polyamide film technology.
Most codes, in the US anyway, require some sort of vapor RETARDER. Vapor BARRIERS are generally only required or desirable under slabs.