[quackaddict]

Hey all, have a question regarding insulation in my 1950's ranch home.

I have recently began demolition of the interior portions of two rooms, combined they have a dimension of 11x20 and this space has two exterior rooms. My plan is to take both rooms and combine them into a master bedroom with a walk in closet and a small bathroom.

I know from gutting the attached garage that the house is insulated with rock wool, seems like it has an R rating in the 2-5 range, I plan on gutting the entire space to the studs and of course re insulating with Fiberglass and adding a vapor barrier.

Wondering if it will be worthwhile to add 2x2 shims to the existing studs to facilitate 2x6 insulation. On the face it seems easy enough and should slow heat loss considerably over the current setup. Would there be enough return on stepping up from 15 to 19 or 22 to make this worthwhile?

I sit here now with the news reporting temperatures in the -30 range tonight...

 

[joecaption]

You would also have to add jamb extentions to all the windows and door jambs.
Since you already have it all torn apart I guess it would be worth it.
Spend the time to air seal any holes where any wires or plumbing were run.
Air seal the attic, make sure there's enough insulation in the attic.

 

[quackaddict]

I'm aware of the jam extension issue, the windows already have them and I'm confident I can remove those and add the thickness I need. The garage was a perfect training for sealing this room, took forever!

I had planned on adding more insulation to the current attic insulation once poly barrier and drywall have been added. It has an r40 installed in 1980.

 

[AGWhitehouse]

Running a layer of foam behing the gwb would give you much more of an impact than extending the stud widths. Use 3/4" polyiso (R-5 +/-) and un-faced batts. You'll need extensions as joe said including your electrical boxes. you should be able to get mud rings for that additional depth.

 

[quackaddict]

The rooms will receive the total redo, including electrical, so I'm not worried about that. I would imagine the foam would be used to stop air flow?

I have been looking for air penetration in parts of the house I have opened up, from what I am seeing the stucco is doing a good job of preventing air penetration. I do like the idea of the foam board thou, should be close in r value to what I could get and would ensure minimal air flow.

 

[HomeSealed]

Have you considered spray foam? Obviously it is more $$$, but you could get the extra r-value without all of the furring, etc. Dense packed cellulose would also be better per inch than the fg batts.

 

[AGWhitehouse]

I would imagine the foam would be used to stop air flow?

It's purpose is to reduce the thermal bridging of the studs. Stopping air flow is achieved through caulking and following the Airtight Drywall Approach (ADA to some).

 

[quackaddict]

It's purpose is to reduce the thermal bridging of the studs. Stopping air flow is achieved through caulking and following the Airtight Drywall Approach (ADA to some).

So Im clear you would add it as a sheating on the face of the studs, then drywall over? That seems like an interesting approach. I would imagine you just use longer drywall screws and have at it.

Tuck taping the foam board would help with any sealing issues you havent gotten already with caulking and such.

 

[quackaddict]

Have you considered spray foam? Obviously it is more $$$, but you could get the extra r-value without all of the furring, etc. Dense packed cellulose would also be better per inch than the fg batts.

Havent asked anyone but with the small SQ ft required it may be a viable option. Worst I cans ay to a quote is no thanks.

 

[AGWhitehouse]

So Im clear you would add it as a sheating on the face of the studs, then drywall over? That seems like an interesting approach. I would imagine you just use longer drywall screws and have at it.

Yes..

Tuck taping the foam board would help with any sealing issues you havent gotten already with caulking and such.

You will need to tape it to provide the required vapor retarder system.

 

[AGWhitehouse]

If you choose the spray foam route, you can put 3/4" thickness furring strips horizontally across the face of the studs at 16" o.c. spacing. Then the spray foam can fill the voids to the face of the furring strips thus providing a similar thermal break along the face of the studs as the rigid foam board. I would only recommend 2.0lb closed-cell spray foam which provides R-6.75 per inch of thickness. It can only be installed in 2" lifts, so multiple applications will be needed.

I find open cell spray foam to be a waste of $$. At R-3.7 per inch it isn't much better (thermally) than most batt. products. With a little caulk and patience you can make a batt. wall perform equally well to an open-cell spray foam wall.

 

[quackaddict]

Would it be a better option to attach the Foam board with some sort of OSB Furring strips then attach drywall to those strips? I could knock out a couple of birds with one stone if I attached the strips horizontally to allow horizontal drywall with 100% edges for screwing.

 

[AGWhitehouse]

Would it be a better option to attach the Foam board with some sort of OSB Furring strips then attach drywall to those strips? I could knock out a couple of birds with one stone if I attached the strips horizontally to allow horizontal drywall with 100% edges for screwing.

You'd be losing more room area by doing so, but it's not an impossibility. Using a 3/4" polyiso board would need 2-1/2" gp screws for 1/2" gwb attachment.

 

[quackaddict]

Thanks for the ideas, I have been mulling the various aspects of this over for a while and am probably going to use a slightly modified approach that wont require outlet box extensions and will allow me to use 1.5 foam. I will have the extra thickness of the wall but since Im removing an inch of plaster product and replacing with 1/2 drywall, I should have a net width of only 1/2-1 inch less than the current width of the room. That I can deal with.

 

[Gary in WA]

What is the exterior wall make-up?
If you have wood board sheeting with tar paper, the inside face of the board is the first condensing surface because it is at/near outdoor temperature; Fig. 6, 7; http://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion

Putting foamboard on the inside will create a vapor retarder, which you want in your climate. However, the foam will also keep the sheathing (if any) colder, increasing the condensation there by having a lower dew point temperature. This is the “lowest bang for the buck” from a moisture standpoint, from Building Science, pp.6,7; https://docs.google.com/viewer?a=v&...iYVZpx&sig=AHIEtbRVXHNlbPlXiHMzGIwFLQF3YvmyFw

If you “piece and cobble” rigid foam board between the studs- canned foam to the boards and around the foam perimeter, the first condensing surface will be the inside face of the foamboard. Outside f.b. would be best-- though impossible for you, go with the “next best”. Similar to a wood rim joist- need to stop infiltrating/exfiltrating air movement (multiple areas with individual boards on exterior wall); http://www.buildingscience.com/docu...joist/files/bscinfo_408_critical_seal_rev.pdf

But, it will be warm enough not to worry about as you would if the f.b. was inside, on stud faces. Inside f.b. will also stop exterior solar driven moisture through the stucco (a moisture reservoir), if on the South or West side, from wetting the cavity insulation, degrading the fiberglass R-value by up to 60%; http://archive.nrc-cnrc.gc.ca/eng/ibp/irc/bsi/90-controlling-heat.html

Inside f.b. would not stop any convective looping of the fibrous cavity insulation, where cavity f.b. does stop infiltration from the numerous gaps; http://www.buildingscience.com/documents/information-sheets/installation-of-cavity-insulation/

Then the cavity would remain closer to house temperatures (conditioned by HVAC) rather than cold enough to have condensation on the boards for a much longer time period during the year, able to mildew, mold or rot the wood framing; http://www2.dupont.com/Tyvek_Weathe...rior Insulation Building Science Bulletin.pdf

For your location; http://www.usclimatedata.com/climate.php?location=USMN0448
with an average low of Jan., Feb., and Dec. of 5*F --------- using cavity 2”XPS (R-10) the sheeting temp. at the stud side would be 34*F for condensation there at 27% Relative Humidity with 70* room temperature. With inside foamboard, temperature of the cavity (most of)/sheeting boards would be same as outside temp (5*F) and only 9% RH. Basically, the dew point changes from the boards face to the foamboard face = and a warmer/drier cavity and insulation. Adding more cavity foam raises to temps/dew points. Inside f.b. stops the air (if sealed, though ADA is best), slows the heat but gives a much colder sheeting temperature for more condensation from outside/inside air movement.

You should add some f.b. strips (1-1/2” wide) to the inside studs/plates edge for a thermal break as said already.

Gary

 

[quackaddict]

Gary, thank you for the post,

So I understand correctly, the addition of rigid foam in the cavities to seal them and more rigid foam over the face of the studs would provide the "best" possible for this installation? You would minimize air movement and create a thermal break on the interior of the wall?

 

[AGWhitehouse]

Sounds like he wants you to cut rigid foam and fit it within each stud bay. tight to the exterior sheathing. Then spray foam all those edges. Then put batt. insulation with thickness to fill the remaining depth. Also adding 1-1/2"x1-1/2" rigid foam strips to the face of the studs.

Pretty labor intensive and alot of expensive foam waste...imo...plus it doesn't really provide you with a true moisture retarding system that is code worthy. Code requires a vapor retarder on the warm side in winter unless you have a continuous R-10 foam layer on the outside (for zone 5). With you in zone 6/7, that R-10 requirement is likely higher, if allowable at all. The method explained above does not provide a continuous layer and therefore does not satisfy that aspect of the code. You would still need to provide a vapor retarder (kraft paper facing) at the interior. BUT, with 2" XPS on the exterior side of the cavity, adding kraft paper on the inside would form a double class II retarder system, which is even worse for moisture issues than a continuous layer of rigid beneath the gypsum board.

 

[Gary in WA]

Yep, AGW nailed it, at least in the description. You will have a warmer cavity for the f.g. and air-tight from the exterior air this way. ADA the drywall for air-tight from the interior. Vapor diffusion will be very slight compared to all the gaps between boards for sheathing. Is more work, lol. Is the wall 11' or 20' exterior wall? 16"oc, 14-1/2" between into a 48" sheet= 4-1/2" rip of waste to use in the attic where the roof slope meets the exterior wall...

Gary

 

[quackaddict]

I would tend to agree...

Basically looking at gutting, adding r-15 Fiberglass, then furring horizontally to accommodate drywall (Something like 24 OC with 2x2 and 2x3) and some vertical only to allow for outlet attachment. Then go back and fit 1.5 foam between and use caulk to seal between joints. Then I can drywall over with a theoretical R in the 22 range. I would loose some to thermal bridging in the end but placing the drywall support on horizontal would minimize that.

I would probably also take the time to seal the slat board as best I could with silicone. That in itself will take forever but such is life I suppose.

Does stucco have an air permeability? It seems like this house is very well sealed from drafts and such, I would assume it is from the continuous siding the stucco provides.

 

[quackaddict]

Yep, AGW nailed it, at least in the description. You will have a warmer cavity for the f.g. and air-tight from the exterior air this way. ADA the drywall for air-tight from the interior. Vapor diffusion will be very slight compared to all the gaps between boards for sheathing. Is more work, lol. Is the wall 11' or 20' exterior wall? 16"oc, 14-1/2" between into a 48" sheet= 4-1/2" rip of waste to use in the attic where the roof slope meets the exterior wall...

Gary

One of each, the room has two exterior walls, which is why I want to insulate as best I can...