Framing details for sprayed foam
I’m finally (after 30 yrs ) building a house for myself and Family.WE have decided to use closed cell foam insulation .I just started framing and am now realizing that the methods I’ve used for the past 30 yrs need some adjusting to accommodate this “tight House” technology.I’ve scoured tons of websites for days and cannot find much on building a foam friendly home.The house is a 2 story Farm house..I guess the specific questions I have are : 1..Include the attic (with air handler) in the envelope ? 2..Non vented cathedral cielings and “Elk” shingles…3..Do I really need to match r-value requirements for energy code if the foam products moisture perm rating and air infiltration rating are so different than fibreglass ? How do I approach the building dept ? I’m sure this will stir up the hornets nest and I have lots more questions…fire away…
Replies
I'm sure this will stir up the hornets nest and I have lots more questions...fire away...
LoL! Great way to kick off being part of BT. Welcome in!
You may get some suggestions to use the Search function--those suggestions will have some validity.
1..Include the attic (with air handler) in the envelope ?
2..Non vented cathedral cielings and "Elk" shingles
You will get a slightly better responce if you fill in your Profile info (click on your name in blue or the gray "Update Profile" at top center) so we'd know where your "here" is. Aspen, CO is a different answer than Athens, GA, or Calgary or Portland (pick one, any one<g>).
Now, Building Science almost always 'wants' air handling equipment inside the conditioned envelope. Whether that's the attice, or the basement or the crawlspace or none of those has a lot to do with your house & its design.
3..Do I really need to match r-value requirements for energy code if the foam products moisture perm rating and air infiltration rating are so different than fibreglass ?
That depends on not only the AHJ (Authority Having Jusridiction), but on the agent of the AHJ. Some BI (Building Inspectors) vary; some vary from job to job, too. What kind of BI you have, we don't know. Froms some of the tales told by Canadian posters, their BI/AHJ can be the most "by-the-book." But other places can be as strict if not more so.
How do I approach the building dept ?
Generally, politely. In my town, I'd say submit what you want to do. If they don't read your exceptions and changes; and just redline the plan, then, often enough, the resubmittal gets an ok. (After they actually read your citations and exempting science, etc.) Other towns differ.
I filled in some of my gory details to make it easier . I will also say I have a good relationship with the building dept. The foam insulation is not completely new to them but it is to me . I am so used to a "breathing" house that I get confused about what to do...not so automatic anymore plus the fact this is finally "Mine" and of course I dont want to make any big boo boos.I do want to have the house look architecturaly correct,overhangs,exterior trim ,porches... Where does the envelope begin and the exterior start ?..see I told you ...questions
see I told you ...questions
Well, that's good, there's plenty of answers here--some are actually worth something sometimes <g>.
Does make it tougher if you are going to ask about that near-philosophical argument about "how tight should a house be?"
I'm of two minds on it. For new work, I'll hold to a higher standard overall. For old work, you kind of have to work with what you have. That means remodel work gets to fall somewhere in the hazy middle.
Since you are in NY, it might be harder to get an "atypical" installation. Your climate will have most people designing tight, and assuming an air-recovery unit of somekind to maintain indoor air quality.
Hmm, now I need to go back to the original post to remind myself what the scope was again, lest I pontificate myself right off the road into the ditch <g>.Occupational hazard of my occupation not being around (sorry Bubba)
Bikerdad,
too bad you've already started, but it's not too late.. look at SIP's and you will have your answers. Spray foam is a compromise between the advantage of SIP's and conventional construction.. you still have a thermal bridge every 16 inches.
In the end it is less expensive to build with SIP's but stick building is comfortable to most people so they compromised..
too bad you've already started, but it's not too late.. look at SIP's and you will have your answers. Spray foam is a compromise between the advantage of SIP's and conventional construction.. you still have a thermal bridge every 16 inches.
Wasn't there an article in FHB a while back in which they created a 6" wall using 2x4s with every other one offset to the inside or outside, which eliminated the bridging?
I know I saw it somewhere.
Old House Fan,
Stick building will never be as strong or as thermally efficent as SIP building.. I've seen offset studs but talk about added costs! Think about it objectively. If you introduce cold 3 1/2 inches into the wall and then terminate it with an inch and a half of insulation will that be as thermally efficent as no studs to intrude?
Untill you've built with SIP's you will never understand just how inefficent the use of 2x material is..
Tip up a Sip panel in place and note just how ridgid that panel is.. Now compare that to a wall built with 2x material and plywood.
Stick building will never be as strong or as thermally efficent as SIP building.. I've seen offset studs but talk about added costs! Think about it objectively. If you introduce cold 3 1/2 inches into the wall and then terminate it with an inch and a half of insulation will that be as thermally efficent as no studs to intrude?
Frenchy,
Maybe you misinterpreted my post - that's so easy to do in here. I'm not advocating building that hind of wall, I just mentioned it as part of the conversation.
I am just a homeowner/DIYer but from what I've read and seen, I'm a fan of SIPs. Heck, I guess you could call me SIPFan, LOL, but they aren't the only answer.
I do think if you used foam the 1 1/2 inches would make the transfer minimal, and better than a "regular" wall, but not as good as it could be.
old house fan,
I think I understood the point you were trying to make and it's certainly valid.. Especially if you are trying restore an old house as your name suggests..
In addition I think your location affects things as well. For example I live here in the frozen tundra just below the artic circle in Minnesota. It gets so cold here that profanity freezes and you need to wait to the spring thaw to hear it.. (maybe that explains all the spring blizzards we have around here, they arrive just to cover up all the melting profanity.. <G>
Yes as you suggest double up the studs and offsetthem will gain a lot over traditional stick framing, sorry if it seemed like I was saying that SIP's are the only answer..
I think I understood the point you were trying to make and it's certainly valid.. Especially if you are trying restore an old house as your name suggests..
I actually considered using SIPs to replace the roof on my carriage house. It's 30 x 32 with a 12/12 roof, no insulation and, to my inexperienced eyes, questionable framing. Unfortunately, in small town midwest I just can't justify the expense.
In addition I think your location affects things as well. For example I live here in the frozen tundra just below the artic circle in Minnesota. It gets so cold here that profanity freezes and you need to wait to the spring thaw to hear it.. (maybe that explains all the spring blizzards we have around here, they arrive just to cover up all the melting profanity.. <G>
To borrow a phrase, one of the coldest winters I ever spent was a summer in International Falls. We had homes there and I went up there in winter - ONCE. <g>
Old House fan,
I bet you'd be surprised where they make SIP's. Mostly in smaller towns. For example I bought all of my SIP's from Lister Prairie Minnesota.. It's a small town west Of the twin cities in Minnesota. The next nearest town is in Marshall Minnesota and then Fondulac Wisconsin..
I know of several other plants in Minnesota.
I in stall open cell foam and can tell you there are only 2 things to do.
1)leave off the vents all of them.
2)add in a good air exchange system.
other then that build it how you want to!!!
foam insulation will fill all the nooks and crannies that you create, that you couldn't get with FG.
that out of the way I now have only 1 question
why closed cell?
closed cell 1"= R-7...open cell 1" = R-3.5 Nys energy code R-18 exterior walls...I framed in 2x4 to save money to help offset the cost of foam and I'm a bonehead.I hate using 2x6 unless I'm going up 3+ stories.It is a waste....Oh by the way ...where are you a "FoamMan" I'm in Warwick NY.........?????
My understanding is that the R-value of closed cell will decrease over time. Something about the gas trapped in the cells dissipating. Whatever the reason, In the end you may not have the full R-7 value.
Based on my searching around here, icynene is much cheaper R for R even if you assume R7 is the value you'll get long term from the closed cell polyurethane. According to more than one local insulator/foam applicator who do both systems locally here, polyurethane closed cell is pretty much reserved for existing construction where 2x6 walls aren't an option.
But again, do something to reduce the thermal bridging or you'll be wasting a significant benefit of the foam. The "Mooney wall" (search the site for details) or 2x4 staggered studs on 2x6 plates will do that for you, each with their own benefits and disadvantages.
You have 2 options
1) see if the building department will use performance value over R-value.
2) there is a denser open cell foam (1.2 pound) on the market it has a 4.7 R-value.
Oh I am a FoamMan in Northern Illinois serving all of northern IL and Southern WI, including Chicago.
BD,
Welcome to BT. I'm the foam installer Bigman mentioned in his post. I'm in East Longmeadow, MA. About 2.5 hours from you. I have traveled out your way for jobs in the past. I use Corbond (closed cell) and two different open cell formulations. See my web site, SAFCOFoam.com for more info or to contact me.Conserning your original question... I would leave at lease a 1/2" gap at joints in the framing that would hide an air pocket. Like an interior wall framed off the exterior wall. Sometimes there is no gap in the framing to shoot into. Leaving just 1/2" here would really help avoid an air gap in the envelope.Shower stalls on outside walls are usually installed when I arrive and they have FG between it and the exterior wall. Thats fine but it can be left a foot short so I can shoot down and cover as much as possible with the foam.At the rim joists in the basement and between floors please leave at least a 4-5 inch gap when the joist runs parallel to the wall. This is so I can spray in at a resonable angle to fill that space.I'm sure I'll think of more. You just gave me an idea for another page on the web site, thanks!Stu
Hey MAsprayfoam: nice site.
A question for you, in line enough with the original intent of the thread that it's not really a hijack:
The rapid high-expansion open-cell foam materials like Icynene and the stuff you're selling: I presume that these materials don't exert any pressure on the structure while they're foaming out and curing, right?
Here's why I'm asking. I've got a cathedral ceiling which for code/inspector reasons I must vent. My sheathing is installed on 2x2 furring across the rafters, and I'm required to provide an additional inch of spacing under that. I was originally going to use foil-faced polyiso board on spacer blocks to also provide a radiant barrier, but I haven't been able to find it locally for less than an arm and a leg. My local installers aren't charging much to foam my rafter bays out a little deeper, so there's virtually nothing to be saved by using a thicker EPS sheet on spacers to provide the required vent space.
I figure I can't use the commercial foam insulation baffles because they wouldn't cover the entire space between the rafters and the foam could just sneak past them and fill up the space between the 2x2 strapping and the sheathing during foaming. The best thing I can figure to use is like 1/8" hardboard (Masonite) or 1/2" EPS. Any other suggestions? Any risk that the 1/2" EPS would collapse upward during foaming, eliminating my vent space?
Thanks for the feedback on the site. I just put it up a month or two ago.The foam expands in all directions with equal force until it meets resistance. Then, it will exert some force but will expand in the direction of least resistance. Kind of if you ever tried to pop a balloon by squeezing it and it bubbles out where your hand isn't.I had a customer do the venting that you talk about. Inside the roof, in each bay, be put in 3/4" blocking on each side then 1" foam board tacked to that. That left little room in some areas for the R-30 spec. Not to worry- we used Corbond, R6.75 per inch so 4.5" is the full R30.I'll upload these pictures once I get a chance.Stu
Good to know that what I'm planning will work. But I think it'll be 1/8" masonite/hardboard rather than 1" EPS foam, given the EPS doesn't offer any real benefit, costs more and is weaker.
I'll be furring out my rafters with yet more 2x2s underneath to get more depth for more R value, so I can use icynene for both walls and ceiling. My local guy is basically charging only $0.25/sq ft extra for the extra depth of icynene, so maybe I'll be furring with 2x3s or even 2x4s on edge. Nice thing about all this is that I will have no thermal bridging through the roof framing, and those 20' long 2x8s were a lot easier to throw up than 2x12s would have been!
<Hey MAsprayfoam: nice site>Where did you see the link?I don't see one in this thread, what did I miss?
MAsprayfoam was careful to NOT post a link that some web-crawling bug could find and use to send him spam. But he did give all the info you'd need to construct a link. Just look up his posts.
Peek in his profile. There is a link there, but taunton does something to pooch it. Once you get the error page, just cut and paste the last part into your browser
Do your customers rough in their electrical before you foam?
They used to let that happen here, but now it is a requirement that electrical wiring be run inside the foam layer, and of course after foaming, so as not to have buried wires.
Stinger-
I read this before when your BI first decided to make up his own rules apparently. That is really a bad turn of events. Why doesn't the IRC require this procedure. You're BI must have done extensive research and studies to require such extra work from everyone involved. If using open cell, 3.7 per inch same as FG, can you do electrical first? That would be just like putting a slit in the batt and slipping the wire in. I would have to fight that one tooth and nail... but you can't fight city hall they say. Has anyone challanged this that you know of? Stu
UH, re: "Leave off the vents all of them", I assume you meant, "leave off all of the roof vents, all of them" because?????
NotAClue
if your using foam you don't need roof or eves vents.
you do need stink stack venting and the appropriate mechanical venting.
Hi , check with your local building department, if they have adopted the IRC, with open cell foam (air infiltration is figured at 0.1ACH) R11 is equal to R19 in FBGL and R20 foam is equal to R38 in FBGL. There was a guy hanging around here named Stu who I had many conversations with about this, which eventually led to me calling Icynene to get the info I needed for my building department. My house is being roofed next week and I need to start looking into it again myself
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Keep in touch with me on this.The info I'm getting is all over the place as are the prices...