Need advise on foil foam foil insulation
Royalt
| Posted in Energy, Heating & Insulation on
Hi This is the first time I posted here i live in upstate NY .I have the upstairs of my house gutted i packed out the walls to 5 1/2 ” I was searching on google for a radiant foil to install in my attic .I came across this website they sell reflective foil barrier and a “Prodex Foil foam foil ” its only 1/4 ” thick and they claim it has an r-value of r-14.5 . Is this stuff legit ? its so thin I dont understand how it gets an r-14.5. If it is , whats the best way to install it along with a 5.5″R-21 ? I want to boost the FG r-values ,get a radiant barrier for heat in the summer ( reflective insulation )and a vapor barrier . They claim that FG is transparent to radiant heat gain and loss Its about .30 sq. ft.
Thanks in advance ,
Roy
Replies
That sounds like the claim of the bubble wraps like Astro-foil. They only acheive the claiomed R-14 in certain instancs with a min 1" of dead air space separating it from other materials and surfaces. Once placed in a wal, that no langer exists. They also make assumptions for reduced convection loss in addition to the radiant heat loss tho it is questuionable whether both can be prevented concurrently with their products and methods.
We often use a foil faced foam panel to add insualtion and create a thermal break spanning the studs or rafters or joists. thermax is one product name. It is polyisoanurate foam with foil on both sides and is rated at R-7.2 per inch by conventional testing means. Installing with taped seams can provide not only reduced dew points, but a VB also. We usually nail it to studs, then nail strapping over it for spacing and SR nailer. This will add to the thickness of the wall, but worth it in most applications, IMO. You can buy it from 1/2" to 2" thickness
The sort of material you first mention might possibly be of benefit in some attic applicaions in hot climates
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Thanks for the input I like the idea of the rigid Hi-R on the wall studs I think I am going to go that way. On the ceilings ,I framed them down to 8' I was planning on using R-38 . Can I install the Hi-R on them as well ? . What kind of FG should I use up there Kraft faced r-38 ( I never saw it unfaced ) ? or unfaced r-21 and r-19 blanket over that then installing 1" rigid foam board like you are describing and tape the joints ?
Roy
I almost never use FG batts. Better to blow cells or chopped FG. Far les convection heat loss. Yes, you can use the Thermax on cieling applications and then blow or roll out your other insulation above it in the attic. I suppose if I had to use FG batts, I would use unfaced R-19 and roll it both ways - at right angles to itself on the second ply. The Thermax would be the VB, so no need for faced.
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I'm with the regulars on this one. The foil faced Thermax is the vapor barrier do not add another with faced insulation. Better yet blow in cellulose.
Keep warm,
Garett
Piffin : What do you mean by strapping and SR nailers ? Do you use furring across the foam @ 16 or 24" for an airspace , and then add something else for sheetrock ??
Roy
strapping is a NE name for furring. We can buy it milled to about 2-5/8" x 3/4" and 14' or 16' long. Run at 16" OC perp to framing on cielings, but can go vertical on studs in walls
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Piffen : Damn its 50' colder here this mornin than yesterdays spring like temps .My gas meter looks like one of those money machines printing out dollars today
So when you use the 1" rigid board are you furring it out for an airspace between the rigid and the SR ? Or are you furring it out just for SR nailing thru it ?
in order out to insheathing
studs
foil faom
furring
sheetrock
That photo was taken before the strapping/furring was put over the foil on the cielingthat leaves 3/4" radiant space behind the SR to reflect heat to interior in addition to the actual R-value
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Got it .Thanks a million .
Roy
I have been looking into different rigid foam board .The super tuff r board is blue on one side and foil on the other .They said the blue side is 3ply aluminum poly and the blue side with the writing should face in towards the room .Is this board the same as the board that has the shiny foil on bolth sides ?? Its about $4.00 less a sheet ?
Roy
Royalt,
No, I don't belive it is the same. I think you're talking about Thermax. With the foil on both sides, it is fire rated for exposure and has a higher R per inch I think.
Garett[edit]
Edited 1/20/2006 9:10 am ET by Grott
I have seen in ebay a mylar reflecitve film..emergency space blanket type stuff ..in large rolls. I wonder how this would work. As you can see in Piffins post the foil covered foamboard has a dead air space due to the furring strips which is necessary for reflective insulation to work. We did a large cold storage facility and used 2 layers of 2'' Iso all seams taped. My 1950's house has foil faced sheet rock. I assume it is more for a vapor barrier than insulation factors.
not sure
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Has anyone used radiant barrier paint on the underside of the roof decking. I have an attic I want to finish but the rafters are 2" x 6". Not much room for insulation in the cold winters here in MI.
Any suggestions to get to R-38 in a 6" space?
Joe I have another house that i have the same situation . Its my brothers It was built in 30's 2/8 rafters and 2/6 cieling joists . Its a full walk in attic . It has a slate roof . Here is the problem . When it snows the snow only stays on it for a short time then it all rips off all at once bad heat loss,no ice dams . We have been afraid to insulate it because there is no drip edge only grown mld under the slate and no snow & Ice barrier . It needs to be insulated . I have been toying with the idea of installing FSK on it .FSK is a foil on bolth sides w/ fiberglass in the middle . I am hoping by putting it on the underside of the rafters and blowing in 6" in the cieling joists that it will stop the heat in the summer and hold it in the winter i was going to have Owens corning thermacube blown in but i came across an articlw while doing a google search and it says that Owens Corning has pulled it off the market in Minnosota ,evidently they have found out that in very cold conditions it looses 30 % or more if its R value .Dont ask me how im only reparing what it said and Im not exactly sure of the % it claimed and i think it said Minnosata but it did say they were pulling it .
Roy
Spray polyurethene foam in place.R-7 per inch more or less at 5.5" = 38.5
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Thanks : I think I will go with the foil on bolth sides
Roy
Piffin : Any special tape for the joints or any that you have found better than othere ? I have some Tyveck clear tape i thought that would be good to use
Roy
good
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Foil tape would be better.
'Nemo me impune lacesset'No one will provoke me with impunity
I just finished my project . Thanks for all the advise you guys gave me . I used r-21 in the walls and 2 layers of r-19 in the ceiling . I covered walls and ceiling w/1" foil foam and furred them out . Drywall was hung over that .
The apartment is on the second floor of a two family house . I had my instant read thermoter there and outside it was 30' inside on the first floor whic was recently redone but not insulated as well as this apt. was 58' upstairs with no heat installed it was holding at 50' .I think the extra work and materials will more than pay for themselves
Thanks a lot for the advise . I have another problem and its my own house I'm going to post a new topic on it in a bit thanks again
Roy NY
As Piffin noted, this stuff doesn't work at all without an airspace. I don't know many that do what is required to give it the airspace it needs, and by the time you do, the poly foam piffin mentioned would probably have done a better job all around.
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Rob: Thanks , I agree . I saw some 1 1/4" rigid foam board with a kraft face on it . It was a lot less than the foil one but i wonder if it is a good ? They said tht roofing contractors use it instead of the foil???
Interesting website . I really like those control boards . I may be interested in something like that at some point .
Roy
well, as with most insulation I rarely see rigid installed with an airspace, so the reflectivity of foil is not particularly helpful.However as far as vapor barriers are concerned, I am not qualified to comment.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
the ones made for roofing are generally much less insulation value because they have to be denser to support foot raffic, materials, and snow loading.
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I've been checking into the rigid foil foam myself to place on the roof decking and cedar shakes over that. They sell 2 inch at Home Depot with R14 value in 4 x 8 sheets for $29. That's less than $1 per sq ft. I guess you can cut it to fit your attic. Checked out the prodex and was skepyical of there R value claim.
Kevin
with things opennned up , no need to cut it. Better to leave it spanning across the joists to prevent thermal brdging
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