r13 iceynene vs r-25 fiberglass
thought i had made up my mind to go with iceynene on a flat roof (black epdm rubber), 3-4 inches blown up on the underside of sheeting gives me about a r 13.i like that its quick and easy verus hanging fiberglass overhead. but i keep reading and am finding out foam isn’t perfect (even though the close cell seems pretty close but cost more $) and have got to looking at fiberglass again. i can put r25 for half the cost of foam and get twice the r value but i would have to install ( i love itching in july). also have thought about blowing cellouse in and could probably get up around a r35 for about the same price -more labor. anybody got any opinons? thanks larry
Replies
The foam R value is an actual, or close to it.
The fiberglass R is a theoretical perfect installation R, not a real world R.
The cells are real Rs too.
Joe H
The only negative I've heard of for foam, and I think it was open cell, not closed, was that if the roof ever leaks, it's very hard to find the source of the leak. Of course, the roof should never leak, but.... (There is a system where foam is sprayed on top of the deck and I've heard you definitely don't want to do that, because if there is a leak, the foam acts as a huge sponge until it leaks through the deck and then there's no way of tracing it and you pretty much have to tear off all the wet foam and start over.) All you grammarians out there, sorry for the run on sentence!
that is one of my concerns, i have a flat roof-it will leak someday. i'm afraid the water will come into the sheeting and spread without a indication from underneath. sheeting starts to rot before you know it.now when you get up on the roof and replace sheeting you are going to lose that spot of insulation. so from what you said about r value do you think i'd be better off to blow in cell vs the fiberglass batts. it would be a little difficult,all i can think of is to hang 2 rows of rock,then blow about 10-12 inches then hang 2 more rows etc.. it would be a pain but i do think it would be pretty effective way to get a good r value at a reasonable price. thanks larry
It was JoeH who knew about R-values, but your idea sounds okay to me. Probably better than putting holes in your sheetrock that you'd have to patch.
The concern about finding a leak, if ever, does not enter this decision. No matter what the insulation, a leak in a flat roof is found by an experienced person and techniques on the top that have nothing to do with the insulation under. It is 50% instinct based on experience. Leaks in flat roofs often travel and send false signals.
my first choice here would be for a sprayed on foam, icy or ury, then cells, then - naw, I wouldn't even think about FBG
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I will second what proffesor Piffin said.
i really don't understand the dislike of fiberglass from every body. i understand it loses some r value at like 35-40 degrees, but if you have a r25 and you lose 20% you still have a r20 compared to a r13 foam. now the argument i hear is the foam makes it air tight in the attic space,bringing it to within say 5 degrees of the condition space.my opinion on that is (and it's worth exactly what you paid for it) is part of the reason for the narrow margin is i have leaks around light fixtures, air ducts, plus convection through the clg.that is helping condition the air. one of the biggest problems i have with foam is the installers i've talked to ,their telling me that i'm paying for 3 inch nominal,when in realty it can run in some spots to 3 1/2 to 2". i'm worried that there will be more 2 than 3 and you know what his reply will be when he's asking for the check"i told you so,pay me " and i'm stuck with a good solid r9 insulation.with fbg i at least know i've got the nominal amount. anyway enough of my worthless theories
I won't argue that there may be local problems with your installers, but the leaks you mention are the very thing that prejudices me against the FB, especially in this scenario where there is a tight roof immediately above and no chance for venting. The foam eliminates the chance of dewpoint condensation ( which can present itself as tho a leak) while the FB will encourage air infiltration that brings the warm damp air to the cool roof sheathing surface to condense.
R-value in insulation is primarily resistance to radiant heat loss.
FB has a great deal of convection heat loss that is not even considered.
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ok,you guys have convinced me on the fiberglass to chuck that idea so on to plan b and here it is. starting at the underneath side of sheeting- place a stryfoam baffle so there is a 1" free air space. then i go in and fit a 1.5" pc of stryfoam r-5 between the rafters and locate it at the bottom of the clg joist ,probably hold it there with a metal strap running across the clg joistevry 4',leaving about 12"space then go in and hole saw a hole about every 2'. then get a cell blower and fill the cavity completly with cellouse.then stick the plugs back in and hang rock. i'm guessing i'd end up with about a r35 cellouse insulated clg. question is will this be ok as far as condensation and should i put a 6 mil vapor barrier between the stryofoam and sheetrock or not worry about . any better ideas welcome...... i'm just having a hard time coming up with a solution on this flat roof .oh by the way tommorrow i have to load up a whole p.u load of insulation and take BACK!!!! thanks guys lol larry
place a stryfoam baffle so there is a 1" free air space.
What the hell is this air space for? Now you are going to try to vent this space? To where from where?
fit a 1.5" pc of stryfoam r-5 between the rafters and locate it at the bottom of the clg joist ,probably hold it there with a metal strap
What is going to hold this foam in place? What is going to keep the cells from blowing past the edges?
You will need to get some gun foam for this. Cut the foam a bit small and then foam it in place between the rafters. That should hold it, the metal straps I can't see so don't know what you've got going there.
Forget the VB.
You're making this complicated.
Joe H
man after rez busted my b lls i've been scared to post -maybe i could get over in cooks talk .lol anyway in reading even on foam they suggest a 1" air space ( article in jlc ) i don't have the perfect vent system being a flat roof. but i do have a continous soffit vent (2.5"x 32')that runs the length of the roof,so i think their would be some air exchange. i take it that you feel if i fill the space plum full of cell insulation no vent is needed? i just don't want to miss some simple detail and 5 yrs from now i'm ripping sheetrock down to dig out wet insulation, how much fun could a guy have . thanks for your time on this. larry
Spray foam will fill the vents, or fill them then blow the cells. Either way, I have no knowledge of what the expeted air flow might be on a flat roof. Maybe whatever prevailing winds you have would encourage some flow, but maybe not too.
Foam or cells, it's all better than FG.
Joe H
ya but he still hasn't profiled what state he's from. ;o)
i know you people in ohio think the us border stops at the missippi but kansas is a state and not a providence of canada. read my post to you ,you'll know everything about me that ya need to know unless were getting married! larry
Roar!
I stand corrected.
It's true, it's none of my business if someone does or doesn't fill out a profile on here.
Those that don't outnumber those that do, maybe that means something.
Marriage is out of the question. You are always overbudget and it'd take too many years to pay the thing off.
be a freebird
lay an egg
my wife is a much slower learner than you- took her 20 yrs to learn how to double my cost estimates,and i do let her make the mortgage pymts every month. email me privatly some time and i'll give you the story on profiles and how idoits can use them larry
The guys that blow cells just staple up a membrane/net and blow. No need for the upper channel vent because you will have enough R-value to eliminate dewpoint consdensation and if you still worry, you just add vapore bar below the rafters later to keep the moisture out.
now, if you think you want to add faom below too, why bother with all that ripping and fitting? Just surface then entire bottom of the rafters right across with full sheets of foam panel board of whatever kind you like. Tape the seams and that becomes your VB too.
Or - put up the foam sheets - say maybe foil faced like Thermax - and run strrapping over it to give you good purchase for the sheetrock later, and to add strength for holding up the cells. Then pump the cellulose above to pack'er full.
But for my thinking - spraying four inches of foam direct is the better job and the least work.
There are studies from Corbond that show that once you go beeyuond four inches, even in a ceiling or attic, you have crossed the line of diminishing returns really fast unless you are in the Yukon or Siberia. The ciy guys repeat a lot of the Corbond findings without refering directly to them because not quite all the same info transfers to the icy foam which is a bit less good. Maybe five inches of icynene instead of four of urethene....
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My understanding is that as the temp approaches 0, so does the R-value of FG in an open attic. If it was only 20%, then no big deal. Sealed in a wall, or anywhere where there's no free flow of air, then it works OK. But cellulose or foam almost always work better. BTW, FG only works well when it's installed almost perfectly. I've rarely seen that. Foam and cellulose are both much easier to install perfectly. IMNSHO, the only advantage that FG has over any other insulation is that the companies who make it have great marketing.Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it.
>IMNSHO, the only advantage that FG has over any other insulation is that the companies who make it have great marketing.
And it keeps the Pink Panther off the unemployment rolls.
always- you've posted 150some posts, been here almost a year anyhow, have put nothing in your profile regarding location, ask a question regarding vaporbarriers and insulation in a flat roof approaching thought of potential R-35 and still don't say anything about location or if it is a whole roof or a single room.
Going from R-13 to 35 is quite a jump. A flat roof makes me think you are out of the snowbelt if you considered R-13 as ok. If so, and your down south a ways, real R-35 will be overkill for your needs.
Ok, forgive me, I'll lay the gun down now.
You sound like a homeowner wanting to do this himself as right and easy as possible within reason.
Easy way, go buy Dow 2inch blueboard 4x8 sheets from the local big box, cut them with a slight taper to fit between your rafters and hammer them in tight with a 2x for a tension fit, make as many layers as you need to pacify yourself.
Then put 1/2 inch foilbacked celotex insulation board to your rafters and foiltape the seams, marking the precise location of the rafters so when you screw your drywall up there you never miss a rafter and make a hole.
for what it's worth
be an R-35
cheers
man i hope that gun ain't loaded-i'd be full of holes. first on my profile i'm on another forum for mustangs and someone went in and searched those profiles and started sending a bunch of junk emails -they must have way more time on thier hands than i do! so i'm a little leary at putting much info out on the net unless i know where it's going. so heres the short version handyman, landlord,basicly jack of all trades master of none.at the moment what i call "rebuilding a house" 2000sf old house completely gutted,all the rooms changing etc.adding a 1100 sf addition/basement.i hate flat roofs but that is what work out best for this paticualr spot. 550 sf under the flat area. location southern ks. not a lot of extreme weather here but we do hit 105 to 0 sometimes. now i personally don't think r-13 cuts this deal and that is why i'm making this so complicated. everybody says use foam,so i have the guy come out he tells me "oh 4 inches nominal will be fine that gives you around a r13 -r15" . i've never used foam product before but that just don't sound like enough. sure i could have him blow in another 4 but my cost now is like 2.50 a foot which brings us to the homeowner asspect. i'm the one paying the bill and i am looking for a good result for the lowest dollar-nothing wrong with that and as my sign on name indicates we are already over budget and will probably continue that way,but mt dw told me to double the figures before we started,she was probably closer than me at the final cost. i've check into the dow board, i'd feel ok if i was hiting around a r-20 even though i don't think thats overkill. by the time i stack dow 3 layers deep i'm at about 1.75 a foot and might as well just icenene it and go on. and that may be what i end up doing but i'd sure like to spend less than a 1000-1200 to insulate 550 ft. anyway thanks for the reply,keep that gun handy you never know when i'll post again!!!! lol larry
Dow board is the most expensive choice.
Beadboard is a helllllllll of a lot cheaper, with less R per inch, but more R per $ than extruded board. Type II is the most common, about 4 R per ".
Current price is about $.12 BD' so a 4'x8'x1.5" sheet is about $8 today.
http://www.afprcontrol.com/rcontrol/ContactUs/default.asp
They sell direct, you have to buy it by the block & they slice it however thick you want it. About 24 sheets in a 3' block, your local (Denver) factory may be using larger blocks. You buy the whole thing whatever size it is.
Joe H
Andy,
You do get air flow in a stud cavity with FG.
Admittedly, not like in an open vented attic with the wind blowing.
But you do get the convection loop of airflow where the cold outer sheathing cools the pockets of air next to it while the room side air is being heated by the radiant off the sheetrock. That warm air is risin while the outer cool air slides down and in at the sole plate to replace the warn air that has risen. The loop is established and heat is carried outward at the top plate to be cooled again so heat is lost to the outside wall.
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get em rez, make them fill out they profile, get the profile cops out, citzen arrresst citzen arrresstt.
Don't put down the gun...
now go fill out yur own profile while I erase mine...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming.... WOW!!! What a Ride!