I haven't had to worry much about continuous insulation in my work, but Illinois is on the 2015 iecc so now I do.... I have a project that I designed with our standard insulation and now need to add a while bunch somewhere to pass comcheck. Is there a max reasonable level of rigid insulation to put on the mtl deck? If I have r-35 on the roof and cont. r-12 below the slab I can maintain my r-19 walls. I believe (correct me plz) that the below slab insulation is cheaper and easier than some gymnastics with cont wall insulation below a variety of ext. claddings. Thoughts?
Non Sequitur
Dec 6, 16 8:26 am
I have my own version of this where I practice and it gets a little ridiculous. What we do where we can't get a reasonable continuous R value behind cladding (masonry piers for example) is deduct that area as if it were windows. That's because we're allowed a certain % of glazing which is considered less performant that continuous insulated walls.
But R19? you're lucky... I'm working with R24 to R28 for walls.
curtkram
Dec 6, 16 9:11 am
it's always best to design the building to code from the start, which means prescriptive method and continuous insulation and all that.
the other way to do it is get your MEP to do an energy model, and use a very efficient mechanical system.
shellarchitect
Dec 6, 16 9:31 am
interesting, we are starting to get a lot of work in IL all of a sudden, I may have to use that trick in the future. R-19, not sure how much longer that will be allowed, climate here is a little different than canada eh?
Non Sequitur
Dec 6, 16 9:44 am
^just a little different.... says I, whom just last night broken his shovel clearing his driveway of snow.
I kid you not.
Wood Guy
Dec 6, 16 12:19 pm
Heat loss to the ground is less than to outside air, in colder climates anyway, so you get less bang for the buck with sub-slab insulation. It's usually more cost effective to add insulation at the walls or roof, but if you already have the project designed, the least impact may be with sub-slab foam.
There is an environmental penalty to using foamed plastic, as the two most common products, closed cell polyurethane spray foam and XPS(extruded polystyrene rigid foam) have blowing agents that are 1000X worse than CO2 in the atmosphere. Once the blowing agent off-gasses, the R-value of the foam drops down to much closer to that of a more environmentally friendly foam, EPS (expanded polystyrene), so I just spec EPS from the start, when I have to use foam. The R-value of EPS is stable.
TedTedTed
Dec 6, 16 8:06 pm
In the history of all the posts that I have read over the years here at Archinect, this might be the most infuriating one. It essentially amounts to "Hey, help me pass this ComCheck (or ResCheck) by gaming the system. I don't actually care enough to design a building that will function well."
Wood Guy - I generally start with Polyisocyanurate because it ties back to a number of UL-tested wall assemblies (which Chicago requires). I know polystyrene is hard to get through because it generally doesn't pass NFPA 285 flammability requirements. I have been leaning more towards Roxul or Mineral Wool insulation of late, though, to try to get further away from the more harsh products (from a chemical-perspective).
So, I'm a little confused. You haven't been dealing with continuous insulation prior to the adoption of at 2015 code? The 2012 edition of the IECC had plenty of requirements for such things. The only way out of continuous insulation is using the U-value chart.
Single wythe masonry is, basically, a thing of the past. I can't seem to get this across to clients who think they can just build any old CMU building they want.
shellarchitect
Dec 7, 16 8:15 am
Bluto, We do use continuous insulation of coarse, usually along with single wythe cmu at the back of a building, but not the extent apparently required in the 2015 IECC. Unfortunately this particular building has a pretty high percentage of storefront which doesn't help anything.
That building science link is great, spent days on it back when I was deciding on a basement insulation system. May have used mineral wool if is was more easily available here
Wood Guy
Dec 7, 16 10:42 am
TedTedTed,
"I generally start with Polyisocyanurate because it ties back to a number of UL-tested wall assemblies (which Chicago requires). I know polystyrene is hard to get through because it generally doesn't pass NFPA 285 flammability requirements."
"I have been leaning more towards Roxul or Mineral Wool insulation of late, though, to try to get further away from the more harsh products (from a chemical-perspective)."
I'm on board with that. We are using Roxul Comfortboard as continuous exterior insulation on Fine Homebuilding Magazine's first Project house, which I designed. I avoid foam whenever I can but sometimes it's the only thing that will work well.
senjohnblutarsky
Dec 7, 16 11:40 am
I priced mineral wool for my house. At 3 and 4 times the cost of other systems, I can't justify that stuff.
Wood Guy
Dec 7, 16 12:20 pm
It's always a complex analysis, and not right for every situation by any means. Like foam, it has its place.
shellarchitect
Dec 7, 16 12:22 pm
love fine homebuilding mag, congrats
senjohnblutarsky
Dec 7, 16 2:12 pm
Has the OP had anything done for a dewpoint analysis?
When having one done on my house, I ran into some really odd results. Granted, my climate is a little (ok ok, a lot) on the mixed side. But, according to the analysis I was setting myself up for a decent amount of condensation. Location of the insulation relative to various types of vapor barriers is something to be considered. Just meeting code requirements isn't always a good idea without a sound understanding of how you're doing it.
shellarchitect
Dec 7, 16 10:18 pm
Have not done a dew point analysis, used EPS for my basement so likely not needed. Perhaps a good idea for current project. Will have more insulation in the walls, turns out insulating the slab only would use twice as much, bad idea
I haven't had to worry much about continuous insulation in my work, but Illinois is on the 2015 iecc so now I do.... I have a project that I designed with our standard insulation and now need to add a while bunch somewhere to pass comcheck. Is there a max reasonable level of rigid insulation to put on the mtl deck? If I have r-35 on the roof and cont. r-12 below the slab I can maintain my r-19 walls. I believe (correct me plz) that the below slab insulation is cheaper and easier than some gymnastics with cont wall insulation below a variety of ext. claddings. Thoughts?
I have my own version of this where I practice and it gets a little ridiculous. What we do where we can't get a reasonable continuous R value behind cladding (masonry piers for example) is deduct that area as if it were windows. That's because we're allowed a certain % of glazing which is considered less performant that continuous insulated walls.
But R19? you're lucky... I'm working with R24 to R28 for walls.
it's always best to design the building to code from the start, which means prescriptive method and continuous insulation and all that.
the other way to do it is get your MEP to do an energy model, and use a very efficient mechanical system.
interesting, we are starting to get a lot of work in IL all of a sudden, I may have to use that trick in the future. R-19, not sure how much longer that will be allowed, climate here is a little different than canada eh?
^just a little different.... says I, whom just last night broken his shovel clearing his driveway of snow.
I kid you not.
Heat loss to the ground is less than to outside air, in colder climates anyway, so you get less bang for the buck with sub-slab insulation. It's usually more cost effective to add insulation at the walls or roof, but if you already have the project designed, the least impact may be with sub-slab foam.
There is an environmental penalty to using foamed plastic, as the two most common products, closed cell polyurethane spray foam and XPS(extruded polystyrene rigid foam) have blowing agents that are 1000X worse than CO2 in the atmosphere. Once the blowing agent off-gasses, the R-value of the foam drops down to much closer to that of a more environmentally friendly foam, EPS (expanded polystyrene), so I just spec EPS from the start, when I have to use foam. The R-value of EPS is stable.
In the history of all the posts that I have read over the years here at Archinect, this might be the most infuriating one. It essentially amounts to "Hey, help me pass this ComCheck (or ResCheck) by gaming the system. I don't actually care enough to design a building that will function well."
Wood Guy - I generally start with Polyisocyanurate because it ties back to a number of UL-tested wall assemblies (which Chicago requires). I know polystyrene is hard to get through because it generally doesn't pass NFPA 285 flammability requirements. I have been leaning more towards Roxul or Mineral Wool insulation of late, though, to try to get further away from the more harsh products (from a chemical-perspective).
This guy has a ton of great info:
https://buildingscience.com/document-search?term=&field_doc_topic_tid=All&type%5B%5D=8
So, I'm a little confused. You haven't been dealing with continuous insulation prior to the adoption of at 2015 code? The 2012 edition of the IECC had plenty of requirements for such things. The only way out of continuous insulation is using the U-value chart.
Single wythe masonry is, basically, a thing of the past. I can't seem to get this across to clients who think they can just build any old CMU building they want.
Bluto, We do use continuous insulation of coarse, usually along with single wythe cmu at the back of a building, but not the extent apparently required in the 2015 IECC. Unfortunately this particular building has a pretty high percentage of storefront which doesn't help anything.
That building science link is great, spent days on it back when I was deciding on a basement insulation system. May have used mineral wool if is was more easily available here
TedTedTed,
"I generally start with Polyisocyanurate because it ties back to a number of UL-tested wall assemblies (which Chicago requires). I know polystyrene is hard to get through because it generally doesn't pass NFPA 285 flammability requirements."
That makes sense. I only do residential work and this product has decent ignition and flame spread resistance: http://www.foam-control.com/?pdf=/Foam-Control%20EPS%20-%20TechData.pdf.
"I have been leaning more towards Roxul or Mineral Wool insulation of late, though, to try to get further away from the more harsh products (from a chemical-perspective)."
I'm on board with that. We are using Roxul Comfortboard as continuous exterior insulation on Fine Homebuilding Magazine's first Project house, which I designed. I avoid foam whenever I can but sometimes it's the only thing that will work well.
I priced mineral wool for my house. At 3 and 4 times the cost of other systems, I can't justify that stuff.
It's always a complex analysis, and not right for every situation by any means. Like foam, it has its place.
love fine homebuilding mag, congrats
Has the OP had anything done for a dewpoint analysis?
When having one done on my house, I ran into some really odd results. Granted, my climate is a little (ok ok, a lot) on the mixed side. But, according to the analysis I was setting myself up for a decent amount of condensation. Location of the insulation relative to various types of vapor barriers is something to be considered. Just meeting code requirements isn't always a good idea without a sound understanding of how you're doing it.
Have not done a dew point analysis, used EPS for my basement so likely not needed. Perhaps a good idea for current project. Will have more insulation in the walls, turns out insulating the slab only would use twice as much, bad idea