Continuous Rafter Baffles
My contractor is going to start doing the detailing of the attic on Mon. I’ve read a number of posts about making a continuous channel from ridge vent to soffit which then is blocked down to the rim joist (If that term is correct). I’m just a little unclear about what material to use. I intend to use 1×1 on the inside edges of the bay (fastened to the rafter) and then over that…this is where I’m not clear. I’ve read I could use masonite, luan, 1″XPS or even osb over the 1×1. What would be the most practical of materials or the best, and what thickness. Should it then be sealed with accoustic sealant on the inside, making it as tight as possible? Anything else I might have missed? I intend to make the attic part of the conditioned space. Thanks and Happy Holidays.
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More information is necessary. This is a renovation, right? And you want to create a vented, insulated slant ceiling? How deep are the rafters, why kind of insulation, what will be your air barrier? Where are you and what's your climate zone? What's the roofing going to be?
Yes, complete renovation. I'm in NY climate zone 4. I want a vented, insulated, slant ceiling. The rafters are 2x8. I havent decided what type of insulation to use yet, any ideas? Not really partial to foam. The roof is a new 50 year shingle roof with 3/4 sheathing (I found out too late that I could have put foam board on the roof). My wall are going to be dense-pack cellulose.
Oh...and I have a few valleys with so called dead heads. I have a few new decorative peaks over the old, so I guess its a little complex. It was originally a standard hip gable type side split. The roofer also ended up covering 20% of the ridge vents which I just noticed.
Eric,
If your roof has valleys that prevent eave-to-ridge ventilation, I'd recommend closed-cell spray polyurethane foam -- without ventilation channels.
Eric, Call and talk to Doug at Northeast Sprayfoam. I only trust these guys as spray foam is a bit tricky. They have Icynene, which I feel is the only foam to spray. Post your email if you would like me to contact you about my experience.
http://northeastsprayfoam.com/
Eric,
Unfortunately, you've limited your options by not taking care of venting when the roof was redone. You could either follow Martin's advice and use closed-cell foam to meet the R-38 standard for your climate zone (Icynene won't do it), or build the ceiling down with gussetted sub-rafters (if there's enough headroom), dense-pack 12" of cellulose and create a good air barrier ceiling below that.
Northeast Sprayfoam is the way to go if located in the Northeast and doing away with a vented roof. They have all foams and they have experience, and I highly only recommend them. Robert needs to work with them and then he would know enough to post about them. We disagree. Leave it at that.
AJ,
You're free to worship at the feet of your foam installers and your foam building guru, but Icynene cannot provide R-38 in a 2x8 roof.
AJ,
Why don't you tell us what the total assembly R-value us, since you're so hot to trot on that?
Before it was non-specific Icynene, which is universally know to be ½ pcf foam at R-3.7/inch if perfectly installed. OK, let's try medium density at R-5.2 if perfectly installed.
Even assuming a 7" insulation depth (which would be pretty hard to do uniformly in a 7¼" cavity) and framing 16" oc, we get an assembly R-value of 28.4. Adding drywall, roof sheathing and air films might bring it up to R-30.8.
Sorry, you lose.
Thank you all for the input. I like the idea of filling the dead heads, but am not big on spray foam. If I only filled the deadhead bays which are only about 10 or so, then have a continuous baffle in the rest of the bays with 1x1's and 2" xps, air tight. Try to extend the rafters down two or three inches which is all I really have space wise, and finish off the rest with fiberglass or dense-pack followed by drywall? What do you think?
AJ,
I've been using whole assembly R-values for 30 years. You only preach about them, but apparently don't even know how to calculate them.
Eric said he didn't like foam, but you're still hunting for converts among the heathen.
AJ,
You can't have it both ways. You rail against insulation R-values and their use in code, but then you want to get extra credit for the sheathing and air films when your insulation choice doesn't meet those code minimum values.
And let's not forget that meeting code minimum means you've earned a D- (you haven't quite failed).
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R-5.2.inch x 7.25 inches (100% full rafter bays, perfect installation) = R 37.7.
Does not meet code minimum. Doesn't even earn a D-. You flunk.
Facts are facts. Propaganda is propaganda. BS is BS (and it ain't building science).
AJ, you can't round up from an F to get a D-.
Maybe you need to reread Martin's blog: "It’s OK to Skimp On Insulation, Icynene Says"
How difficult is it to understand the term "minimum requirement"? The minimum requirement for a passing grade is a D-. Meeting the minimum code requirement earns a builder a minimally passing grade: D-.
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AJ,
I hardly need to reread anything, since I never miss a word or a punctuation mark (though it is often difficult to make sense of your incoherent statements).
"Take it personal"... "attacking me"...
I have, and will continue to, critique non-factual statements, poor or erroneous logical arguments, propaganda in place of science and all the other BS that you consistently spew onto these threads.
It is, in fact, you who take this all too personally - both by sidestepping my arguments by claiming them to be attacks on you and by using ad hominem responses such as:
"Robert, yaa dinglepuss"
"37.7=38 moron"
"yaa loon"
"Man up"
If you want to make a New Year's resolution to start contributing something constructive to this forum rather than your constant and unrelenting blather, bias and ignorance - it would be a great service to GBA.
But don't tell me to change the very necessary role I perform here, which is confronting BS in whatever form and from whatever source it appears.
If you would like not to feel so personally targeted, then stop posting such obvious targets.
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What's the matter AJ - don't want to leave the evidence behind?
You don't get to erase the past. You have to take responsibility for what you've left in your wake.
[Deleted at the request of A.J. Builder]
I dont want to cut into the argument but,
Thank you all for the input. I like the idea of filling the dead heads, but am not big on spray foam and the cost for the whole thing. Since there are only about 10 or so dead heads in a valley,how about if I only filled the deadhead bays with R-30 bat or maybe sprayfoam and then continuous baffles in the rest of the bays with 1x1's and 2" xps against that, air tight. Try to extend the rafters down two or three inches which is all I really have space wise, and finish off the rest with fiberglass or dense-pack followed by drywall? What do you think?
You'll be far better off with dense-pack cellulose than fiberglass.
Cost is definately a factor. If I go with dense-pack in the dead-head rafter bays then continuous vent with the foam board over 1x1's, does that sound good?