hey guys,
i’ve run into a small problem concerning insulation in a shed dormer on an old cape. the rafters are 2×6 24″ on center, and the dormer rafters are only 2×8 16oc. the ceiling is a cathedral with ridge venting, so i’m going to need baffles under the decking. i had an insulation contractor come by, and he advised me that i’m going to run into some heating bill problems because the bays are just too shallow and the best he can provide is r13. he offered a closed cell sealing foam in addition to fiberglass batts, but at an additional 1.50 per square foot that’s not an easy decision, and it technically doesn’t add to r value. another contractor offers icynene, but i haven’t gotten his estimate yet. anybody have any thoughts as to how to resolve this? i could fur the rafters, but how much is necessary? thanks in advance for any advice
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i could fur the rafters, but how much is necessary?
Fill out your profile and maybe we could guess how much you need. Are you in California or Vermont?
Forget the ridge vents and baffles, dense pack it with cells.
Joe H
"it technically doesn't add to r value."
I don't understand that at all. Closed cell foam runs a dollar or so per board inch, and is rated about R7 per inch - twice as much insulation as FG while being even more effective at sealing off infiltration. which is the downfall of FG batts.
icynene is about R3.5
Polyiso is about R7
EPS is R5
best way to go is to do away with the vent baffles and spray solid bays 5" deep with closed cell foam for R35
Second best would be to dense pack cellulose or FG BIBBs
and then an inch of foil faced polyiso with taped joints, then strapping, and sheetrock. with 5" fill, that gives you R25
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thanks for taking the time to give some much needed advice. as far as my post about closed cell foam not providing any r value; i'm not an insulation guy, so i can only repeat what the insulator told me.. i'm under the impression that he wasn't planning on filling the bay with closed cell foam, so much as using a closed cell caulk to caulk seams, and then following up with baffles and fg batts. his words were technically the r value would remain r13, but it would be more efficient than r30 with the seams sealed. i don't know if that makes sense to anyone else. i've decided to get 2 more estimates from companies that spray closed cell and icynene just to make sure i get my options straight
good idea. Sounds like either you misunderstood him or he is shooting you a line of bs
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his words were technically the r value would remain r13, but it would be more efficient than r30 with the seams sealed. i don't know if that makes sense to anyone else.
Makes sense to con men.
Keep looking, and maybe check with Ancy C, he's on Long Island.
Joe H
The efficiency will increase as long as the con dog stays attached to the photo ramis on the quey.
It almost sounded from description like he was going to use a small cannister to seal penetrations at edges for infiltration, but charge top price for a full inch of foam.
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Yeah, and charge whatever he can.
Joe H
thanks again to all for advice, got another measure just today where i was advised there's an option to put 1 1/2" of foam to underside of roof sheathing, followed by blown in blanket, combined with full foam depth in 2x4 walls. apparently the cost would triple if i were to go with just foaming the rafter bays completely. he's going to email me prices for different options including just going with the r13 batts. guess we'll see on monday,
thanks again, bryant
1 1/2" of foam to underside of roof sheathing, followed by blown in blanket, combined with full foam depth in 2x4 walls
Sounds like the real deal this time, go for it.
Joe H
Don't know if he mentioned this but you might want to check if he is going to at least put cardboard to the sheathing if not baffles. I don't install spray foam but I know that the reputable guys around here will install cardboard if they aren't using baffles. It will prevent a replacement of the insulation if you ever need the sheathing torn off. Of course that hopefully won't happen but it is what I would do on my house "just in case." The closed cell foam is at least triple the fg price in the quotes I have heard. However r13 under a roof is a joke compared to current standards. And then again - that's what my roof has and it seems to be doing fine w/ at least 15 yrs on the shingles so far. Maybe I'm foolish but I worry about potential ice dams from escaping heat more than I worry about the cost of lost heat.
thanks for the cardboard idea. another thing i hadnt considered is i may need to install an air exchanger into the hvac system if i go with foam in walls n ceilings because of how airtight the house will become. my biggest question is how many years it will take to break even with the added expense of using foam. i'm in waiting mode for estimates, but its safe to say i'm looking at a couple thousand dollars over just using standard fg. i'm eligible to retire in 10 years so tough decisions ahead
Wonder what the cost of fuel will be in five or ten years, that might effect the pay-back. Bet it's more expensive then than now...I'm thinking that the added cost of the better insulation would be worth a lot in ten years and almost assuredly long paid off by then as well.------------------
"You cannot work hard enough to make up for a sloppy estimate."
I believe that your most important consideration is going to be the final r-value. Spending 3k more for unventilated r-27 roof would not be worth it in my opinion. The age and warranty on your roof, and rating of windows are other considerations. I know one guy tells me that his customers don't have to heat their attic anymore because all the heat that escapes from the house is trapped there and so it not only eliminates the cost of heating that room but retains the loss of others. Great pitch but I like things on paper. If the installer presents a proposal w/ r-values for each option it would be easier for you to reconcile the differences in cost by researching the options. You should be able to rough estimate what it currently costs to heat/cool the room and then compare the percentage differences. Yes, I know that is very rough but it's a start to the decision process. The amount of time to break even will depend on the amount of insulation, the amount of area insulated and the areas that aren't (old windows).
While I like the appeal of foam, I know about as many guys hesitant about it as I do who are fans. Just venturing my thoughts because this interests me. Hope it helps but I am not an expert on insulation. It seems like every time I have adopted a position on it there emerges some new research or opinion that throws me for a loop. A client I am working for right now has r-50 in walls and ceilings. Will she really get her money out of that? It makes her happy and that's what counts...I guess.Here's a link to the product she uses. http://p2insulation.comI have no idea what it costs but I bet it isn't cheap. One of the videos says that r-values are out-dated...so I probably should stop typing and just shove my hands in my mouth to tickle my foot but anyway... Edited 5/17/2009 5:13 pm ET by bcarpentry
Edited 5/17/2009 5:38 pm ET by bcarpentry
The area heated is a very small concern in heat loss calculations.It is the area of wall and roof surface exposed to exterior temps ( along with window type and uvalue) that is the primary concern. Once a volume of air is warmed or cooled, to temp, there is no energy expended to keep it that temp no matter how large that space is. The only BTUs expended is to replace what is lost thru outer surfaces.So in a cape, there really is very little energy used to heat the upper.
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Thanks for straightening me out on that. I think it clarified the point I was stumbling around guessing at. If I'm understanding so far than what would measures would you use to decide on the form of insulation? Obviously the more the better - but not at the cost of a ventilated roof...unless that's a line that we've swallowed for years. I guess r-value is getting outdated as there are too many elements to have a simple numeric summation of a room without considering all the exterior components. What steps should he take to measure the financial merits of each option?
cost to install is always a major factor in anyone's decision. Nobody who has ever gone with the foam has regretted it. I get feedback with exclamation points on that.but combo of foam and blown cells or FG does well too.I rarely use just FG batts. It is the worst choice possible. Too much convection in it to carry heat outside.You are VERY right about r-determination being outdated. The testing is favorable to FG batts and was developed when that was the only real choice.The measure of BTU loss is taken with only a 10°F differential on opposite sides of the wall, not enough to cause any significant convection loop.but who in the world even bothers to turn the heat on when it is only down to 60°F outside????!!!! Take the measurement with a difference of 40 or 50 degrees on opposite sides of the wall and FG batts is laughable as an insulation by comparison to all the others.
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One thing to consider in all the talk of cost and payback is the difference in comfort between a house that is cheap to keep warm and one that is always cold because of the cost of heating it.
You can bet the price of heat is only going to go up, once you save that $ now it's too late, you're going to be cold forever.
Joe H
man this is not getting any easier, but everyone's advice is keeping my head from spinning.
well, i just had someone get back to me from a large well known company out here, and here are my options in black and white
i could go with batts and baffles in ceiling:
r15 in the 2x6 rafters + r21 in the 2x8' on opposite side
r15 in walls
white caulk plates + closed cell non-expanding foam for doors and windows+fire caulkor if i'm willing to double the price of the job
1 1/2" foam + fill remaining depth of rafter bays with bibs for approx r25 to r35 in ceiling and the rest stays the sameor triple the price and everything is airtight foamed wall and ceiling.believe it or not, their guy didn't try to push the expensive options and instead advised me to go batts and baffles because it would probably take at least 5 years to just break even. that isn't to say it makes the decision easy because the advice i've received in this forum is weighing very heavy on my mind. i'm waiting for 2 estimates to come in and then it's get it done time......thanks to all for taking the time to help, bryant
Keep in mind that those R-15 values in the walls for FG are for an absolutely perfect laboratory install, which is not the real world.
How bout an inch of foam everywhere & blown cells to fill the cavities?
Once you close up those walls with batts, you're committed to a cold house forever. The air flow through the batts, the convection currents in the walls are npt what you want.
Joe H
"those R-15 values in the walls for FG are for an absolutely perfect laboratory install, which is not the real world.How bout an inch of foam everywhere & blown cells to fill the cavities?"Carry the details out...That R-15 FG batt will perform more like R11 in cold weather, if that much.While the other option you mention will actually perform at about R-22
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"because it would probably take at least 5 years to just break even."at what price fuel?????Somebody hinted at this before, but may have not underlined it enough to pay attention to, but the payback at $2.50 oil vs at $4.50 oil is different.General rule of thumb used to be FG or cellulose insulation added paid for itself in three years in a heating climate. Ever escalating cost of BTUs has to be considered.
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what Piffin said. Closed cell foam and do away with the vents.
I used icenyne when finishing my basement in an old leaky house. I found that the price was very reasonable as compared to closed cell foams. In fact, the price was not much worse than dense packing blown insulation. I found this out when I was getting quotes for our new house - which has not been built.
When planning out our new home, we ran into a similar problem. One area of the house had vaulted ceilings. My was decision then and will continue to be to choose the icenyne foam - hands down. But you need to retool your way of thinking about insulation and ventilation of unconditioned space. Fill your entire void with the foam - no dead space at all. Don't worry about soffit vents or ridge vents. If the installers are good, they should be able to blanket the foam without pushing it out your vents. The vents will serve no purpose, nor will they need to. Hot air cannot enter a space where air cannot go. Heat gain from your roof will be significantly reduced, and air infiltration will be null. 6" of foam should get you about an R-38, so you will be doing fine with your R-Value too.
With the experience that I had with Icenyne in our old, drafty basement - I will plan to insulate our entire home, ceiling and all, with it. Comfort is great, payback is quick.
If icenyne is still not a choice for you, look into dense packing some blown in insulation. You will not have as good as results, plus you will have problems with insulation pushing out of vents when installing. There is the wet application which may solve this problem.
Icynene has about the same Rvalue as denspak cellulose. No way will it provide R38 in 6". More like 22-24 for the open celled foams.
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It's been about a year since I looked at the numbers, but I believe that it was between R6 and R7 per inch.
That is the right value for closed cell polyurethene, not icynene.http://www.inspect-ny.com/interiors/Icynene_Foam_Insulation.htm
" * The poured-in formula for icynene¯ foam insulation has an R-value of R-4 per inch.
* The spray-formula of icynene¯ foam insulation has an R-value of R-3.6 per inch. In new construction often this product is sprayed between joists or studs, allowed to expand and cure, and then trimmed flush with the wood framing surfaces. This smooth application merits the full R-value claimed. If the spray is applied unevenly the R-value of the insulation blanket for the building may vary.
* Spray polyurethane foam has an aged R-value of about R-6 per inch (varies by formula)
"It's pretty common fopr the icy guys to make exagerated claims, so it would not suprise me a bit if they misled you with a statement like saying that it performs euivalent to FG batts at R7/inchPolyurethene closed cell foam starts out at R6.8 to R 7 and loses some as it cures in over time to settle at 6.4 more or less. Icy never begins to come close to that. It does preent infiltration and convection loops in the stud spaces. But I can't tell you how many times I've heard of them making the same claims that urethene has earned, piggybacking on that reputation! There is a reason icy is cheaper.
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Question about a possible misconception I have adopted...I read a while back that in the north a "cold" roof needs about r-50. Is there a standard (thickness) to determine what it actually needs in closed-cell foam to prevent affecting snow on the roof? An installer told me that he sees his roofs covered w/ snow while others have melting/dams but he didn't specify at what point it is "enough."I get hung up on this because I do a lot of sub work that is the result of ice dams. Or maybe I'm just slow...
There are other factors besides R-value, but I do fine at R30 when well done such as BIBBs, cells, or foam.
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Open cell insulating foam, as it cures, forms cell walls (from tiny bubbles) which are broken, permitting air to fill the cells, and typically having a density of .5 to .75 pounds per cubic foot. In our opinion an open celled foam is less resistant to moisture uptake than a closed cell foam, giving closed cell products and advantage where moisture is a concern in buildings.
Open-cell foam insulation should not be used below-grade such as below a concrete slab or outside of buried foundation walls.
Well, so much for my basement installation!
Actually, the stuff has worked great to eliminate air infiltration and blocking the warm air from the cold masonry. I also have a great interior drainage system - which helps.
Open cell definitely soaks up the water if exposed.
There have been reports here of finding that it collects moisture in certain situations like cathedral ceilings to the point that you can wring it out like a sponge.
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