Gentlemen; I am redoing sheetrock in four outside walls, roughly 50 linear feet. This is in northern new england. The walls are 2×4 with 1/2″ ply and tar paper. Should I add one of the types of foam board behind the sheet rock? The 3 1/2″ of fiberglass will be behind the foam. Am I really gaining a more efficient wall? The extra depth does not matter. Or should I just use the fiberglass? I also have put in a better energy efficient window (s) already. If I go with the foam and tape it well, do I have to include the 6mill poly vapor barrier? Thank You
Replies
I ahve always been under the impression that the closed cell foam (pink or blue) well taped on all the joints will do as a vapour barrier. The white cheap foam will not as well as it will crush easily.
I did exactly this in my last home in the kitchen. As the house was built in the 50's and was 2x4 construction as well as ungrounded wireing. I decided that a total tear out would be easier to replace the wires plumbing and insulation. Then I added 1" foam on top and taped all joints. Just had to extend the window jambs. DW wanted wider sills anyways. Plus I like you replaced the windows.
Go for It.
Yes, do it but I would use the foil faced iso foam, marketed here as thermax. it has double the R value per inch as the pink or blue
Excellence is its own reward!
Is that foil faced on both side? If not, which way do you face the foil?
The reason I ask is that I used a foil one side board on the outside of my shop. It is behind steel siding, and the instructions said to face the foil side out. I am guessing that it is radiant barrier on my building.
Just courious as to its purpose with an inside application. I know Mike Smith uses foam (blue) board and strapping in his wall system. He did not mention foil faced board, but if it improves the overall performance, why not?
Dave
I've never seen it one sided. Most of the two sided has white covering on one of the sides though. You apply it facing the side you want heat sent to. In the south, it reflects heat out. North buildings you want to reflect in. To me the most important point is that the iso has better R value. the foil stabilizes and protects it for handling and installation and is a vapobar. This stuff is R7.2/inch. I think the other is R-3 or so. It is needed for contacting water such as for underground or some prefer it for in roofs because of potential for water intrusion..
Excellence is its own reward!
Down is changing the blowing agent on Thermax and respecing it at 6.5/inch. Blue board is speced 5/inch.
That brings it lots closer than it used to be!
I guess the next issue is cost.
.
Excellence is its own reward!
Edited 1/18/2003 12:30:18 PM ET by piffin
Thanks piffin. That was my guess, but never having used it inside, it was just a guess. Seems I remember a thread about radiant barriers on the old board, or should say flameing thread. Followed the whole thing and can't remember if anyone ever proved that radiant barriers worked.
There is a question in my mind whether the foil does much as a radiant when it is in contact with SR or other solid material. The better insulation was my focus and it happens to come with a foil surface..
Excellence is its own reward!
Piffin; I appreciate your resposes, you guys are fast. Any particular method of fastening the foam? Or is it mostly held on by the sheetrock?
I have already had the siding off, when I replaced the windows. And have put back on I have seen a couple houses with serious problems when they used foam on the outside under the siding and moisture got trapped.
In moderate and normal climates, the foam does not belonmg on the outside!
I use plastic cap nails for installing the foam.
Excellence is its own reward!
for our ENERGY walls we use 1" EPS (2.0 lb/cf ) this is twice the density of regular eps.. also we furr the walls 16" horizontally and use 4" sq/ boxes for all of our elec. devices....with 1.5" plaster rings..
before we hang the blueboard we blow the walls with dens-pak cellulose... the furring keeps everything in place.. and provides nailing and blocking for the sheetrock and trim..
EPS is considerably less money than R-max or poly iso.. or Foamul-R or Dow.. the r-value is about 4.0........
if you don't furr, you will have trouble with your elec. devices... and hanging your rock, and applying your interior trim... if you do furr, it will be more labor and money up front... but it all comes out in the wash...Mike Smith Rhode Island : Design / Build / Repair / Restore
"if you don't furr, you will have trouble with your elec. devices... and hanging your rock, and applying your interior trim... if you do furr, it will be more labor and money up front... but it all comes out in the wash..."
I was beginning to think I was on an island by myself.
Tim Mooney
Re-insulating my house in Winnipeg from the inside. Previous owner had replaced windows & re-dashed the stucco. First room was bedroom with 8' wall, easy test. No outlets, one window. Put R12 fglass between studs & 1.5" white foam over top. 2.5" shingle nails to hold foam & 3.5" screws through all to hold drywall. Added extender to window jamb.
Final result after taping; pressure on wall compressed foam causing screw pops, no nail backing for casing around window, and nothing to fasten brackets for window covering.
Present system is; R12 FG between studs, 1.5" Dow bluefoam attached with a few 2.5" shingle nails to hold in place, all joints sealed with acoustic sealent, strapping screwed through foam to studs with extra added for backing around windows, outlet boxes mounted on short 2X pieces screwed to studs, drywall screwed to strapping.
Final result after taping; an excellant retrofit wall system. More work, yes, but well worth it.
Most Canadien provinces and I'm sure many northern states have done research on the best methods of energy conserving construction, both new and retrofit. The results are published and usually available for the asking. It's better to use proven methods then what sounds logical. Case in point; The earlier post on filling the cavity between 2x6 rafters with FG & then covering all with foamboard is a recipe for an icedam disaster. Befor I knew better, I did the same thing myself. When the water started flowing from my ceiling, I caught 30 gallons in buckets. An unknown amount ran down through the walls. There must be a freeflowing ventilation airspace between the top of the insulation and the roofdeck to prevent ice dams. That airspace is equally important in warmer climates where ice dams are never a problem.
I won't go into an explanation of the whys of this because it's longer then I want to go into right now. Contact me if you want more. In the meantime, with all due respect to most posters in Breaktime, it is better to get factual information, backed up by research, then to trust somebodies infallable (G) logic.
Paul
Paul, you could not have explained it any better ! This keeps comming up time after time . Thanks for the response. You are dead on .
Tim Mooney
>>"if you don't furr, you will have trouble with your elec. devices... and hanging your rock, and applying your interior trim...
Tim & Mike,
I know you guys know your stuff. What am I missing here? We use 2 1/2 & 3 1/2 deep switchboxes and make sure they are all secure and level- blocked, shimmed, screwed. That does take a little adjustment time I admit. We use gages for depth.
We use blocking where needed for trim. We shoot casing on with 2 1/2 16 ga.
We must be talking about two different things. I haven't seen a need to furr.
fonz... we are talking about putting 1" foam on top of the studs , aren't we ?
yes, i guess you are... anyways , i've been on the average job where they tried it without furring.... the rock tends to crush... baseboard pulls in the bottoms... 2.5" nails for trim... what does that give you ?
(3/4+1/2 +1+ 2.25.) .. so that 's 1/4" of penetration into the stud...everything has to be perfect.... i'd rather furr... besides... even with 2.0 lb/cg ( high density EPS ) if you blow dens-pak cells into the studs, you blow the foam off the studs....
so furring solves a lot of problems with foam on the walls
Edited 1/20/2003 10:09:13 PM ET by Mike Smith
Mike,
I think the penetration ends up about 3/8 with thinner trim than you mentioned and the nail head 1/8 below the surface. It could be argued that is not enough, and I may be wrong on that.
Another way of looking at it though is there is not a need for nailing trim any harder in most situations. Doors, for example; I shim/screw the jambs 5 places each side centered under the stop. The casing is screwed/glued at the miter (kreg jigged if 3/4, longer nails too) and is just cosmetic. The window trim is self supporting too. The stool screws up into the side casings and the casing is bradded to the jamb extensions. The 2 1/2 16ga finish don't have much to do.
We shim the drywall recess at the floor and raise the BB up 3/8. There you could be right about a longer nail, but I would guess that half the nails will pull through the baseboard rather than pull out.
We have never used the blow in insulation you and Tim have mentioned. We don't have a problem with the R13 unfaced fibreglas.
I think you end up with a great job furring. I just haven't experienced the need.
Now comes me .
Unless drywall has a hard surface that is attachable, its not a product of choice . It doesn't make any difference how you pull your gun . If you want to do things like putting foam on the wall with out furring then don't choose drywall. Use a material that trim can be nailed to like 3/4 lumber ..
Drywall must have the raw wood or metal surface to attach . The first step to building a house is the foundation . The same principal applies to drywall .
Drywall is gypsum lime . When it comes to the job it has been subjected to moisture and its very soft actually. Only after its hung on the wall does it actually cure to its hardness. Therefore it must have a solid surface for successful installation and finish. When drywall is nailed for example , it crushes the field giving way to more weakness. A smaller example of this happens with a screw. When drywall has a soft backer it never gets tight , so therefore loose nails, or screws. With a foam backing there is no stopping point to call it "good " . This same thing happens when nailing siding over foam on the exterior . We have to stop when flush instead of driving the nail home , otherwise the siding wont be in a straight plane. Nails or screws in drywall must be driven home to conceal the fasteners in order to be finished. When this happens the field in the drywall is broken with out a hard surface. An example of this is king stud and a trimmer side by side but unequal. Choose nailing the lowest member that is not meeting the plane and the same thing will happen. The nail will bust through before indenting the drywall.
If that is not enough; Drywall must be held tight through a heating season where it finally cures to maximum hardness. There is notable movement in the whole building envelope as it adjusts. The situation above would have call backs to say the least and you would be responsible to fix it. Judgement for the plaintive in the amount of,........
Tim Mooney
Tim,
You make it sound impossible to install 1-inch rigid foam over studs, and then drywall, without horizontal strapping. But many of us have done it. All that is necessary is careful, accurate installation of the drywall with long screws. I know it works because I've done it, without nail pops, problems, or soft-feeling walls. I'm sure that those who install strapping have a system that works well for them, which is fine. Either way will work.
No it isnt impossible . It just comes down to the quality of work you want to perform. Same thing goes for Mikes example of finish nail length.
Tim Mooney
>>Unless drywall has a hard surface that is attachable, its not a product of choice
Tim,
That was a great description and fits all my experience with sheetrock and you've had more; however, I MAY be talking about HARDER foam board than you are. There is a soft product (ie) called Tuff R that would need furring I agree. The products RBoard and Super RBoard are examples of the hard stuff I am saying you can put sheetrock over and finish away.
We have done it for descriminating customers that would call us back, in fact we HAVE been back for other things, and there is no problem with the sheetrock, either in seam or screw.
Mike; I have a dumb question. You mentioned furring every 16" horizonttly, is this over the foam or do you cut and fit the foam between the furring strips.
2x4s here are cheaper than 1 bys here . Question ;
Why not blow cellulose in the whole 5 inches ? Scrape off at horizontal 16 inch members ?
The way I see it , it would be cheaper done that way if the cellulose would hold. You would have 3.5" to hang ceiling trim and base . I guess you could put a 2x6 on the bottom if you were hanging the wide base .
You would be with out a vapor barrier.
Tim Mooney
Edited 1/21/2003 5:48:57 PM ET by Tim Mooney
cmbb.... 1st we tack the foam, then we nail the furring on top of the foam
tim: if you leave the foam out you don't lose the thermal bridging...the foam is R-4,
i guess if you strap the wall with 2x3 ( adding 1.5 " ) you'd get a theoretical R-5.5 additional... with a thermal bridge every place the strapping crosses a stud.. which wouldn't be too bad...
hmmmmm. .. ok.. my new energy wall is now called a "mooney" wall.....lets say the outside 2x4 stud bay is (R3.7 x 3.5" ) say R-13 , but it is degraded because 10% of the wall is stud (R1 x3.5") say R-4... so the 2x4 stud section is a combined R-value of about R-12, and the combined R-value of the flat 2x3 is about R-4.8 say..
so the Mooney wall would be about R-16...
and a fiberglass 2x6 wall ( R-19) would be a true R-17... but i don't believe this accounts for edge loss with the fiberglass batts....so i degrade the fiberglass wall to at least an R-15..
NOW, our previous energy wall would be (R-12 ) + R-4 (foam) so that would be R-16 also, but the foam is an extra step, and extra money, and you have to fool with the elec. devices, and apply the furring...
so , Tim, i think i like it... my new "Mooney wall"...
here's the process, frame the wall, nail 2x3 @ either 16" or 24" , install elec. devices, plumbing, blocking, apply Regal wall fabric & glue, blow dens-pak cellulose, hang the rock / blueboard...
Mike Smith Rhode Island : Design / Build / Repair / Restore
On the foam with furring and drywall you have a 3/4" air space in there. And with the horizontal furring you won't have much in the way of convective air currents.
It has been a long time since I look at the numbers but doesn't that by you another R point.
yes.. R-1 additional....but i still like my Mooney wall... gonna sell it to the next lucky devil thru the doorMike Smith Rhode Island : Design / Build / Repair / Restore
tim... this is as good an excuse as any..
how are you doing?.. we're worried about you ... hope all is well. your friends miss you
MikeMike Smith Rhode Island : Design / Build / Repair / Restore
Thanks for asking .
I have been trying to keep up with my job and going to school. We are booming here and problem jobs take up extra time . My city not only pays for all the schools I want to atttend but pays me while Im going! I could become a professional student really easy ! I really enjoy going to school and look on it as an opportunity I would not have got any other way. Im entering all the schools I can attend.
On the other shoe Im learning new things every day inspecting. Seems Im always running into something new and having to look it up and review it. Im also getting a self school on how to take peoples Wheaties away from them and keep um smiling . Trades people are a proud bunch and dont like rejection. The last thing they really want is a critic. Ive made the most head way with them being diplomatic and explaining my reasons . Seems most flare ups are just a lack of communication of either them misunderstanding or "me". By the end of the year I might be ready to move to people skills 202! LOL.
Im having a lot of stressful fun ! haha
Ill use this as an opportunity to see whats new here.
How bout you , how are you doing ?
Thanks again and I hope this message finds you well!
Tim Mooney
tim... nothing unusual.. just flat out...jobs and RhodeFest planning..
we are still hoping you will steal the time for you and your wife to come meet these people...
got lots of jobs to figure... some to design...two or three to build... which comes first ?
am just about to do the biggest Mooney Wall yet.. wait until you see the pictures.. you're gonna be so proud
last night we met a couple of new friends.... Mike and Maria Sullivan and their children Angela & Andrew.. came to dinner to help plan the food for RhodeFest
anyways.. to get back to Tim..
don't neglect us... you know that part of your job is teaching now... and what better audience and group of pupile could you have than your friends here at BT
Mike Smith Rhode Island : Design / Build / Repair / Restore
Tim,
Better answer Roll Call
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Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I'm in CT.
If the sheetrock is touching the foil face of the polyiso, then the foil doesn't act as a radiant barrier...it simply acts as a conducting foil. For what that's worth.
My method? Use either cells or unfaced FG batts in the cavities. Then foil-faced polyiso. Though it comes in dual foil or just one side foil, I put the foil face to the inside (warm side) of the room. Tack it up with just a couple of nails w buttons. When you hang the sheets of polyiso, gap the sheets 3/8ths to a half-inch. Also, the seams don't have to break over a stud. When done, use canned foam to fill the gaps between the sheets. Foil tape the foamed gaps, now you have a tight room.
Furr as Mike sed, do the boxes as Mike sed.
Drywall gets screwed to the furring strips. Easy.
If you rock with long screws through thick foam without furring, it's easy to mess it up.
There is a question in my mind whether the foil does much as a radiant when it is in contact with SR or other solid material. The better insulation was my focus and it happens to come with a foil surface.
.
Piff
I wonder if foil does anything at all on insul.
I was at a NARI seminar a few years ago with a Johns Mansville rep and he told me that foil face was going to be extinct eventually as it really doesnt do anything buried in a wall. I kind of agree.
Put your hand against foil faced fiberglass or foam then against the same without for a minute or so...I feel no difference at all.
Just a thought.
Be foiled
Namaste'
Andy"Attachment is the strongest block to realization"http://CLIFFORDRENOVATIONS.COM
You just don't feel right - LOL
It does do a little but I doubt it's worth thinking much about. There are some studies that apply to roofing showing that a radiant barrier as compared to same insulation with no radiant barrier place a space away from the underside of roof sheathing will reduce attic temps but increaase the roof surface temps and reduce the life of the asphalt shingles..
Excellence is its own reward!
You just don't feel right - LOL
It does do a little but I doubt it's worth thinking much about
Piff..Trust me.I feel! I feel that the comparison of cost throughout an entire house of foil vs. not is significant in the savings to think more then twice about.
a"Attachment is the strongest block to realization"http://CLIFFORDRENOVATIONS.COM
The problem with your idea is that the drywall will never be tight for finishing with foam under it . There wood be a lot of people doing the same thing if it were a testament to fine home building. However you may lath on top of the foam if it wins out and drywall from there. Of course that changes everything doesnt it ?
Secondly , you do not mention locale , or the exterior finish. Its a lot easier to add foam on the exterior when accessable. You need to check a builders code book to determine the R value that is needed in your area .
Tim Mooney
I had to do exactly what you described. My roof was 2x6 rafters and the building dept. wanted R-25 min. Obviously you can't get R-25 in 2x6 (with fiberglass). So I either had to sister 2x8 onto them, or here's what I did:
Used Owen's Corning high-density insulation (2x6 with R -21).
I then used 1" Owens Corning pink foamboard on top (gives me another R-5) for a total of R-26
Now, I used UNFACED fiberglass since the foamboard is my vapor barrier. Use that cool aluminum tape (duct tape doesn't seem to adhere too well to foamboard for some reason) at the seams if you so desire.
I used 1 5/8' sheetrock screws through these big metal discs you can get at the Home Depot (discs are like 2" in diameter?) to secure the foamboard in place. (I suppose adhesive may work, but given this was on a 45 degree pitched roof, I didn't want it falling off while trying to put sheetrock on)
Put 1/2" sheetrock over it with 3" screws. It WILL fit VERY snugly for taping and mudding, just be VERY careful to not go too far into the sheetrock. Fortunately though I did not have any butt joints so I can't vouch for that, but I do recommend Instaback (by Preston or something) for buttjoints. (I had walls separating the ceiling sections and was able to use long enough sheetrock to avoid butt joints)
Hope this helps!
--Kevin
Yes, do it! We have done this walls and ceiling in a complete house. We used unfaced R13 in walls, two layers unfaced R19 in ceiling (hold temporary with stapled string). You will see dramatic results with the foamboard.
Whether you use foil faced foamboard or not, make sure it is a firm product, so there is no "spring back"on the screws. We used RBoard or Super RBoard and fit it tight. Tape seams with foil tape. We just used enough roofing nails to hold.
I recommend 5/8 sheetrock walls and ceiling. We use 2 1/2 inch screws on the ceiling, 2inch screws on walls. Screw depth set is VERY critical. We have had NO problems with finish, fasteners, or moisture. I would definitely NOT use any visqueen. We use Tyvek outside, but I think the tarpaper will be fine IMO. I am assuming adequate attic ventilation.