I heard someone mention that they like to build a 2×4 wall and insulate it with fg, then they put rigid foam insulation under the sheetrock to seal the house better. They say this is better than a 2×6 wall. My question is, is it better than 2×6 walls?
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I say so.
Here is why, it costs less and is more structurally sound if you are placing 2x6 at 24" oc vs 2x4 at 16" oc
The foam separates the thermal bridge that a framing member creates to transfer cold to inside.
In a 2x6 wall with FG insulation, you get a theoretical r19
in a wall you describe, the FG provides r13 or R15 depending which you get and then you add R7 for the polyisoanurate foam( Thermax) to get R20 to R22 without a thermal bridge.
Use blown cellulose instead of FG and do even better.
tape the joints in the foam and you have your VB in place
The foam also reduces the infiltration
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Careful guys .
In an earliar post you said you strapped over the foam. Are you still saying that ?
Tim Mooney
Tim, I was jusr replying to the Q about whether it make a better wall, not about every detail and option of how to do it.
In my thinking the strapping makes for a better SR job and easier attachment and we do all strappping here on cielings anyway so it is a small thing to add to other walls too.
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Have you ever had any problems with these walls? I really like the idea and will probably use it on my house. Do you glue the foam to the studs or do you just let the drywall hold it on? Thanks
Currently sitting in a home I designed with foam under the drywall. No strapping. I cannot find any cracks or other defects after more than 6 years in service.
While I can see how strapping might be convenient for running wiring, it does not seem to be required for successful drywalling.
This structure has amazing thermal performance. It's nearly 3x the size of my own old project house, but uses less than 1/2 the fuel to heat.
I built a client a wine room: 2x6 walls on 16" centres, r-28 and put on 1" Icocylene (sp?) panels. I glued 'em and screwed on with 2½" decking screws. The boarder used 4" screws.Quality repairs for your home.
Aaron the HandymanVancouver, Canada
Total rvalue was 28 right? Normal for a 2x6 with FGis R19, then add R-7 for foam and a couple for sheathing and siding?
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Just curious, I'm building an addition now. I had planned on using the foam board on the outside of the sheathing instead of the inside. I had choosen this method from a fairly recient FHB issue. I wasn't going to use a vapor barrier on the inside. Is the prefered method to put the foam on the inside????
If you are in a cooling climate like Georgia or Florida, you want it on the exterior surface of the studs, but in a heating climate, you want the superior insulation and the VB on the inside.
Doing the way you propose, interior moisture would be driven into the wall cavities by heat and stop at the VB/foam panel on the exterior and stay there most of the year, leading to all the problems that wet studs and fibreglass can cause you
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What if you're in a temperate zone? Like NY? Just about as hot and humid as Georgia/florida in the summer, but in the winter we get bitter cold.
NY is a heating climate for the most part. To calculate, you take the number of degree days of heat requyired. and the number of degree days of cooling required.When the two balance out pretty much, as in a moderate climate, it can be better not to use a VB so the wall can dry to both sides aletrnately
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No, R40+.
Here, 2x6 walls have R28 glass bats. The foam board I put on were 1" faced both sides w/glass cloth. They had a rating of R14 or better if I remember correctly. I have all the old invoices around and could pointyou to the web sites, if you are intersted.
Might take me a whileQuality repairs for your home.
Aaron the HandymanVancouver, Canada
I would definitely like a link and if anyone knows whether there is a different rating systrem in place up there - kind of like the exchange rate on the dollar assigning different values to items
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uh, oh... the olde R-14 to the inch , right ?...
hah, hah, hah..
aaron, you got those invoices filed right next to that one you got for the bridge , right ?...
anyways.. not to step between you 2 guys, who seem to be having so much fun without me...
but someone was talking about blowing cells (Dens-Pak) behind 1" foam.. here's my experience..
if you use a strong foam.. like say Dow Styro -SM.. or a 2 lb/ cf EPS.. then you may get by without the strapping.. the caps may help..
however..you have to be so careful that you tempt fate with your blow..you can have blow-outs with the dens-pak blow
we tried using 1 lb/cf EPS and didn't like it.. it was too fragile in handling and fastening.. then if you strapped it ( which we always did ) you could compress it at the edges and lose your plane...
to get reaonable strength and to facilitate handling, we found that spec'ing 2 lb/cf EPS was the best... and then strapping it.. we could blow cells behind that without a worry in the world...and the increased cost per sf was negligable..
now..if you do a cost comparison between EPS and XPS, you'll find a world of difference .. the increase in R-value for XPS is not enough to offset the increased cost
and the minimal difference in moisture transmission behind EPS & XPS is also not a great factor
and the greater moisture transmissivity of the EPS will probably work in your favor in a heating climate allowing for some drying to the interior .
the Mooney wall takes a lot of this into consideration.. with both walls we have the 2x4 stud bay.. and the Dens-Pak cells (3.5" x say R-3.5 = R-12.5 )
then the 1" foam, say R-5 for EPS & a 3/4 air space due to the 1x3 strapping (R-1 )
so, a nominal 18.5
and in a Mooney wall, strapped with 2x2 (1.5" ) we have an additional R-5.25, for a nominal 18.0
so.. the foam wall takes the matl cost of the foam, and the 1x3 strapping..
and the labor cost of installing both
the Mooney wall takes the material cost of the 2x2 strapping , and the insul-mesh.. and the labor to install both
the labor to install the foam vs. the labor to install the insul-mesh is about a wash,
the labor to install the strapping in both cases is about a wash..
the difference is the cost of the foam delivered to the job
the Mooney wall facilitates installation of electric devices and blocking for assessories ( like curtain rods, grab bars, etc )..
the foam/strapping wall is harder to install electric devices in
given the two choices.. we abandoned the foam wall in favor of the Mooney
now.. the question remains: would we be better off with a sub-contract foam insulator to come in and foam the 2x4 stud bays ? what 's the R-value ?
what's the cost ? which foam, Urethane or Icynene ? what other variables enter the equation ?
one is that you CAN eliminate the insul-mesh if you rock the wall and blow the Dens-pak thru the board , then patch the holes.. you don't get the absolute visual inspection that you do with an insul-mesh blow.. but you do save time and labor
with icynene, you overfill the stud bay and then shave the foam flush..
with urethane, you underfill the bay ( the cost and the cure rate prohibits overfilling the bay )
since we've NEVER hired a foam sub, we only know about foam by 2d hand knowledge.. i know it's expensive.. but so is our labor for the Mooney wall
also: are any of my suppositions about foam above incorrect ?
hmmmmm ?
Mike Smith Rhode Island : Design / Build / Repair / Restore
Your statements about the foamed walls are right, except that you have added benefit with foaming that when he is doing the house, he is also hitting the sill/crawl infiltration and attic exfiltration, and not just the walls.
You won't find me arguing against the Mooney wall. I like the idea, just haven't tried it yet.
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Piffin,I would agree that foam is the superior insulation, but when you have a conventional wall you still have the thermal bridging. How do you handle this?
Jon Blakemore
good question - and one I had to think about for a few minutes over this cup of Java.
Because on the jobs where I have used the spray foam, there has been no signs ( Mildewed stripes on the walls) of the thermal bridge.
So I had to ask myself why not?
One thing is that the worst cases of those black stripes was on homes with vinyl siding over osb
The homes where I have used sprayed foam have 7/8" sheathing with cedar shingle siding. That only adds a tiny R-1 value to the wall, but combined with other factors, it might be making a big difference.
Other factors?
>A lot of the cold transmission in cavities insulated with FG is right at the tucked edges between stud and batts. that probably accelerates the cold transmition by contributing cold via the convections there. With the tight seal of foam, that is eliminated
>the interior of a house with sprayed foam insulation has FAR fewer convection loops and cold spots to carry moisture laden air to the cold wall surfaces so the cycle rate would be less. This touches more on the symptom than on the actual thermal bridge, but is nonetheless an important factor to the HO
>It could also be that there are other contributing factors not directly a part of the insulation system. For instance, the client who can afford the foam insulation might also be more likely to be repainting walls more often to keep up with decorating trends or to be including an air exchanger heat recovery system to control humidity more closely
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I'm really wondering now if all this discussion will go away as we start seeing more and more SIP's. Are SIP's really the wave of the future as Kevin Halliburton predicts? I haven't seen much in my area yet.
Al Mollitor, Sharon MA
I for one hope so, then maybe the price will be more affordable.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations.
Aaron, Mike had a Q for you aboove in post to me. Wanted to be sure you found it...
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nyuck, nyuck ,nycuckMike Smith Rhode Island : Design / Build / Repair / Restore
Holiday cheers to you!
make mine a double nyauck
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Ive got a question.
Over and over you and others state that that 2x2 compared to 1x3 is equal cost.
I know we have native yellow pine here and labor is cheaper. Imerg couldnt get over what we build for here when he was here. That said Ill say this ;
Lumber cost and material savings off the job are great using 2x2s. Theirs not any 1x3s being used here except for metal ceilings. Left over lumber and crooked lumber can be ripped and straightened on chalk line lathing. The cheapest lumber we have per thousand is a stud which can be used top and bottom in the Mooney wall.
Is your labor so high that the above is the same money as a 1x3? Or is our lumber really cheap? I figgure the labor is the real difference.
Tim Mooney
tim.. assuming i can get two pcs of 2x2 from a 2x4 , or 3 pcs from a 2x6 and comparing that to 1x3 furring...
they should be close enough to wash.. i'd really have to check lumber prices without shooting from the hipMike Smith Rhode Island : Design / Build / Repair / Restore
I think we pay what most of yall do for material. I think a house material wise costs close to the same except in places that materials may be hard to get to such as an island or off to itself like Alaska. We are sitting on an interstate that puts us in quick touch with East Coast -West Coast. We have the river traffic from the North and are close to being damn South. I think that we are in the middle of Petticoat Junction. Most everybody is linked .
When I attack a house for price , labor is most rewarding to work on. Labor is cheap and materials being set items are standard. We can rip cheap lumber , but 1x3s are premium because lumber yards dont sell them in great quanity. They are normally Yellow Pine. Not my favorite strapping. Plus Canada lumber is cheaper in utility.
I guess what Im saying is that there is no question to me what I would use for strap.
Tim Mooney
Mike,Do you ever have problems strapping with 2x2's. I have never used them in this specific application but I would imagine they would be prone to splitting/rolling.Also what is your nailing schedule for your 2x2's?
Jon Blakemore
john. no problem with rolling or splitting... usually one 12d nail at each stud
tim:
this is New England... we use lots of strapping..
they have lifts of 8', 10' , 12', 14', & 16'.... all spruce
it used to be $.07/lf.. i'll check prices.. it's probably twice that nowMike Smith Rhode Island : Design / Build / Repair / Restore
And Pif ......
I had to read your post twice to find the question;
Honest to Gawd, Mike, your technical posts can be longer than my Rabbi's sermons on a Saturday morning LOL!
Actually, the invoices ARE filed because the job was done in 2003.
I don't understand the reference to the bridge - is there something in your area that has a reference to filing bridges?Quality repairs for your home.
Aaron the HandymanVancouver, Canada
it's an obscure reference , aaron..
season's greetings to you and yours..
Mike Smith Rhode Island : Design / Build / Repair / Restore
And to Piffin ....
I've looked but the stuff is in storage.
I'll be at the lumberyard Sunday for the Boxing day Blowout, but I won't get a chance to ask about the panels - they'll be busy. I know one of the plants is in Texas.
As soon as I get more info, I'll set up the web link.Quality repairs for your home.
Aaron the HandymanVancouver, Canada
tim... our 1x3 spruce furring is $0.18/lf
our kd spruce 2x6 is $0.56 / lf... ripped into 3 pcs will give the same $0.18/lf..
so our material costs us $0.18/ lf , plus the cost of ripping, say $35/ hour on a table saw
collect all of the material , rip and stack it... assume 200 lf of 2x2 /hr = $0.18/lf
so... ripping 2x6 costs $0.18 + $0.18 = $0.36 / lf.
if we had an exterior wall 8x40 , we'd use 280 / lf of 2x2, which would add a material cost of ........... $100 (7 pcs x 40' @ $0.36/lf )
320 sf of wall = an added material cost of $0.33/sf
2x4 wall ( say 440 lf. of framing material only ) costs $150
2x6 wall (same 440 lf. of framing material only ) costs $242, say $100 more than the same 2x4 wall
so, in terms of material cost... the Mooney wall costs the same as the 2x6 wall
so, what we do for our 2x2 is rip all of the clubs and splits laying around
the 1x3 doesn't give enough depth for a mooney wall.. we need that 1.5" depth to give us the added R5..
BTW: i figure the thermal resistance a little conservatively with our cells.. i use R3.5/inch for dens-pak... most use R3.7/inch so
if the inspector is looking for an R19 wall.. i can demonstrate that using the cellulose mfr.'s numbers
(3.5" x R 3.7 = 12.95 ) plus (1.5" x R 3.7 = 5.55 ) = R19.4
which is a lot better than a nominal 2x6 wall with R19 batts .... both will meet energy code for a required R19...
Mike Smith Rhode Island : Design / Build / Repair / Restore
Mike, you need a lesson in bf calculations.
Get a real man's square and study the bf charts...
blueWarning! Be cautious when taking any framing advice from me. Although I have a lifetime of framing experience, all of it is considered bottom of the barrel by Gabe. I am not to be counted amongst the worst of the worst. If you want real framing information...don't listen to me..just ask Gabe!
blue.. why would i use bf in those calcs..?
my price lists are in (per piece ) & lf ...
Mike Smith Rhode Island : Design / Build / Repair / Restore
Mike, it was a joke...a bad joke.
But....Stock Lumber always used to include bf pricing on their invoices and I found it quite easy to quickly determine what the bf averages were/are. I still use my mental formula to quickly figure bf prices.
a 2 x 6 10' long is 10 bf. If it's selling for $4 per piece, the bf foot price 40 cents. Almost all similar lumber in that species will usually sell for the same bf pricing.
I am showing my age.....
blueWarning! Be cautious when taking any framing advice from me. Although I have a lifetime of framing experience, all of it is considered bottom of the barrel by Gabe. I am not to be counted amongst the worst of the worst. If you want real framing information...don't listen to me..just ask Gabe!
heh, heh, heh.....
i like BF prices. but i guess the yards all went to pc price so they wouldn't have to educate their staff...
i like to figure assemblies and then use a typical.. like an 8'x40' wall.. then work that down to a $/sf so i can compare walls to walls
bf works great for framing..
and foam insulation...
but it gets a little cumbersome for siding and sheathing
my CMIV + trig has not arrived yet
happy new year blueMike Smith Rhode Island : Design / Build / Repair / Restore
I wish they still used board foot pricing too.
LF or per piece pricing probably for the uneduacted masses
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Give me bf pricing and a spreadsheet any day over lf pricing.Even without Excel I could remember 10 prices on the job and calculate anything I needed. No way I can remember the 100's of pc. prices.
Jon Blakemore
I guess I'm not so weird after all...
blueWarning! Be cautious when taking any framing advice from me. Although I have a lifetime of framing experience, all of it is considered bottom of the barrel by Gabe. I am not to be counted amongst the worst of the worst. If you want real framing information...don't listen to me..just ask Gabe!
Sorry Blue,Admitting that you're like me will NOT prove that you're normal.
Jon Blakemore
but since yew admitted that you were like him, does that make yew ab-normal?teHee
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Possibly, but I still carry a speed square.Come to think of it I also use DW screws <g>
Jon Blakemore
Thanks for your trouble.
Tim Mooney
Mike,Why not use 2x3's at $.22/lf. instead of ripping 2x6's? You would gain better (at least easier) nailing for trim and save $40 on your hypothetical wall.The only downside I can see would be a slightly bigger thermal bridge.
Jon Blakemore
same price list has 2x3 / 10' at $2.47 ea. say $0.25 / lf.. plus the thermal bridge you mentionedMike Smith Rhode Island : Design / Build / Repair / Restore
Thank you...that was an education.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations.
I definitely find the strapping cheaper than taking time to rip off 2x2s counting labour and I am quite sure we pay close to double what Tim does for labour
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6 inches FG with R-28? I have seen 5 1/2 inche batts at R-21.
It is claimed that with foilbacked foamboard with foil facing a 3/4inch airspace, an additional R value from the heat reflection properties can be gained although nominal in respect to the whole wall thickness.
To acheive that would take the 1x strapping mentioned earlier. If strapping solely for that small Rvalue increase it is questionable if the cost and labor would be worth the trouble.
Sometimes strapping and shimming can be used to provide a bit of flattening stability to horribly warped studs before the drywall.
Personally I have 3 years of drywall screwed through foamboard directly into wall studs with no cracking.
If doing the same to undersized rafters with snow loads and foot traffic on them the possibility of hairline cracks increases.
I use plastic cap nails to hold the foam on, then, I usually run strapping over it for SR nailing/screwing surface
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Would the foam board (with or without strapping) be rigid enough to blow cellulose behind? Most of my experience with insulation has been with fiberglass rolls and batts, but reading here about cellulose from Mike Smith and others has me rethinking proper insulation techniques.
Al Mollitor, Sharon MA
no direct experience from me on this Q, M but I think 1" foam would be strongenough. It is the fastening schedule that I would question. I usually put the foam up with just enough plastic cap nails to hold until the strapping or SR goes over it. I would do a lot more if I were blowing something behind it.
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Has anyone experienced moisture problems with this setup? EPS is more "vapor permeable" than XPS, and foil faced is a vapor barrier. Maybe it works fine in heating climates. Just wondering & I thought I'd spark a little discussion on this issue.
Billy
Mojo,1" faced polyiso board with 1x horizontal strapping would be plenty strong for cellulose blowing. The strapping acts like huge washers to retain the foam on the wall. Use 3" screws to hold the strapping, and it wil be most solid.Bill