Zone 6 - Wall Insulation: building out 2x4 walls

DoItMyselfToo

Hi, I'm new to this site. I've been researching insulating and vapor control for a planned wall upgrade on my raised ranch in Wisconsin (zone 6). I currently have 2x4 walls with poorly installed fiberglass batts. My siding is some old pressboard clapboard stuff that has not held up to the weather, partly due to the previous owner failing to paint dents and scrapes. Moisture caused some limited surface swelling of the pressboard.

I need to come up with a wall system that will help me deal with the vapor control issues within the bounds of a renovation. The underside of my drywall does not have a poly vapor barrier and removing the drywall is cost prohibitive.

Under the siding the sheathing is plywood on the corners and Celotex style fiber board in the field. I'm considering removal of the sheathing and building out the nominal 2"x4" walls using nominal 2"x2" lumber. This would give me an actual wall cavity 5" thick. The new deeper wall framing would be covered with 7/16" OSB. Cellulose would be blown into the wall cavities at higher density to prevent settling. By the way, the small gaps in framing that cannot readily be filled with cellulose would be filled with foam prior to the installation of OSB sheathing. The OSB would be covered in a Typar type house wrap. Then XPS (extruded polystyrene) insulation board would go over the top. Then fiber cement clapboard siding would go over the foam. The drywall on the inside of the home would be painted with a vapor controlling primer.

The cellulose in the wall would be R3.7 per inch at 5" thick, yielding R18.5. The XPS at 1" would add R5, and address thermal bridging.

This wall configuration should dry primarily to the interior based on what I've been reading on www.buildingscience.com. And also from this site, since XPS is rated as moderately moisture permeable, should provide some drying to the exterior as well. The house wrap should provide a moisture control plane over the wood framing to protect it.

Any advice about this method or suggestions for modification would be greatly appreciated. I've got 6 months to figure this out, though 6 months can seem to come quickly, especially if I procrastinate.

Some options I've considered are:

1. Prior to building out the 2"x4", adding diagonal metal cross bracing from top plate to bottom plate at all corners on all four sides of the house. Then building out with 2"x2". Then sheathing with 1" foam first. And then adding the 7/16" OSB. Blowing cellulose in the walls. Finally wrapping with Typar house wrap.

2. I've considered increasing the thickness of the XPS to 2" or even 3".

3. Another option would be to increase the build out by adding 2"x3" lumber, giving 6" wall cavity for blown in cellulose.

Thanks in advance.

Ron6519

If you use a closed cell foam in the current 2x4 wall, you can eliminate a lot of the added construction.
I'd minimize the added 2"-3" foam board on the exterior as the heavy siding would not be supported by hanging that far away from the sheathing. I would use a 3/4" sheathing, not 7/16".
Ron

jerryh3

Go pick up this month's issue of Fine Home building. It has a good article on retrofitting wall assemblies for insulating purposes.

DoItMyselfToo

Thanks jerryh3 for the tip. I'll check that article out.

DoItMyselfToo

Ron6519, I appreciate your suggesting closed cell spray foam. I recently bought a couple of closed cell kits and sprayed my attic floor (the backside of my ceiling drywall, then blew cellulose over the top for a total of R55 of insulation. The foam works great. It's fire rated (E-84) and with a anti-molding properties.

When I calculate spraying my exterior walls, though, I'll spend about $7500 spraying kits and still have thermal bridging. Last summer I called a spray foam insulation contractor, who quoted me 3" of closed cell spray foam in my wall cavities for $5000. That's with me opening two adjacent walls at a time and getting everything ready to spray. I wonder how can the contractor charge me only $5000 including labor, when doing it myself will cost me $7500? I must say when I asked for a quote for my attic (4/12 pitch), he didn't want to take the job.

jerryh3

Which kits did you use?

DoItMyselfToo

Foam It Green anti-microbial E-84 602 board feet kits from http://www.sprayfoamdirect.com/.

Gary in WA

“This wall configuration should dry primarily to the interior based on what I've been reading on www.buildingscience.com. “ --------- Vapor diffusion retarders, when specified in cold climates and very cold climates, are located towards the interior of the thermal insulation. When vapor retarders are used, walls and other building assemblies are designed and built to dry to the exterior, should they get wet or start out wet.

“The new deeper wall framing would be covered with 7/16" OSB.” ------ rated at 0.91 perms or barely semi-impermeable, a Class II. With your v.b. primer paint inside rated at 0.45, another Class II v.b.. IF, and a big IF, OSB doesn’t do so good after it gets wet: http://performancepanels.com/index.c...pp_pp_atr_perm

http://www.eima.com/pdfs/The%20Perfe...r%20Stucco.pdf

If you use ¾ plywood, need to divide the perm rating by 2, which may end up being a Class I -true vapor barrier, depending on the species used.

Have you looked into rain screens? http://www.nchh.org/Portals/0/Contents/Article0440.pdf

http://www.greenhomebuilding.com/pdf/RainScreen.pdf

The SPF has a perm. rating of 1.8 at 1” thick (semi-permeable), did you primer the ceiling inside for the v.b. or no, as cellulose manufacturer recommends? http://www.applegateinsulation.com/C...id=249418&fd=0

Be safe, Gary

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jerryh3

Thanks. I'm gutting my bedroom soon and I'll have around 180sft of exterior wall to insulate. I'm still going back and forth between a 600bf kit or just using Roxul Comfortbatt.

pyper

What about rigid foam on the outside with stucco? I've seen that done and it makes a nice appearance -- I haven't read anything regarding how these type of retrofits work over the long term.

It sounds like removing and replacing the sheathing would be a pretty expensive option. How long is the estimated payback period?

DoItMyselfToo

I like the look of clapboard siding. Fiber cement siding gives the look of wood with added durability and fire protection. From what I've read, fiber cement siding expands and contracts less than wood which is what provides longevity to the paint.

The cost will be a lot of my time and energy, that's for sure. Energy efficiency is my goal along with comfort. I plan to live here until the end of my life and I'm still in my mid 30's.

pyper

Energy efficiency is a good thing, but so is not wasting money. If it costs you more out of pocket to do the project than you will save in 20 years of heating, then I question if the project actually makes sense.

As far as comfort, I just put in a wood stove, and it's the definition of comfort. Cheap to run too, if you have free wood.

DoItMyselfToo

GBR in WA,

Thanks for your reply. I've responded to most of your post below.

****“This wall configuration should dry primarily to the interior based on what I've been reading on www.buildingscience.com. “ --------- Vapor diffusion retarders, when specified in cold climates and very cold climates, are located towards the interior of the thermal insulation. When vapor retarders are used, walls and other building assemblies are designed and built to dry to the exterior, should they get wet or start out wet.****

With warmer summers and the use of central air conditioning, these rules seem less fast and true. In southern climes where AC is used extensively and the big issue is high heat, the "rule" is to encourage drying to the interior. In WI we get 80's and 90's for several months at least. Which rule do I follow? Certainly, not both. www.buildingscience.com talks about drying to the interior and exterior as an option. I've thought about this and have had some concern as drying to the exterior seems like it would discourage mold issues inside the home. Thoughts?

Buildingscience.com says, "A Class I or Class II vapor control layer is required by the IRC on the interior side of framed walls in Zones 4c, 5, 6, 7, and 8, with the exceptions of basement walls, below grade portion of any wall, and wall construction that is not sensitive to moisture or freezing (e.g. concrete block wall). However, BSC recommends avoiding Class I vapor control layers in general in wall assemblies, except in special use occupancies in cold climates such as indoor pools and spas"."

My home does not have a polyethylene vapor barrier under the drywall. There is some craft faced fiberglass batting that was poorly installed. So the vapor barrier is less of barrier. I would like to really increase the insulation in my walls and air seal. I need to do this with a method that will allow drying of wood and insulation. I've thought about a flash (spray foam) and fill (cellulose), both installed from the exterior. This would mean that the foam would be sprayed on the backside of the drywall in the wall cavity and the remaining cavity would be filled with blown in cellulose. What do you think of this as an option?


****Have you looked into rain screens? http://www.nchh.org/Portals/0/Contents/Article0440.pdf

http://www.greenhomebuilding.com/pdf/RainScreen.pdf****

No I hadn't considered this for my home considering I am going with fiber cement, though I had been watching a small bungalow being resided in redwood last summer and a rain screen was used. I'll look more into this for my application. Sounds like this would generally encourage drying of the wall to the exterior of the house. Thanks for the PDF's.


****The SPF has a perm. rating of 1.8 at 1” thick (semi-permeable), did you primer the ceiling inside for the v.b. or no, as cellulose manufacturer recommends? http://www.applegateinsulation.com/C...id=249418&fd=0****

No, I did not add the VB primer to ceiling because the foam is my VB in this application. I need my ceiling drywall to breath into the living space. Do you see any issues that I should be concerned with using this method?

Thanks,
DoItMyselfToo

Gary in WA

“I've thought about this and have had some concern as drying to the exterior seems like it would discourage mold issues inside the home. Thoughts?” ---- I agree. I would use fiber cement siding on furring, builder’s paper, plywood, some rigid foam (taped and sealed), studs with cellulose, drywall and an interior latex paint. At the corners (and every 16% of footage or Building Department codes), have the ply/foam reversed to meet wall shear flow. The cement siding (reservoir cladding on p.t. furring) would be uncoupled from the building, the paper- 6 perms; the foam -1.5 perms. per inch or 0.9 perms for 2”; ply.- 0.7 perms; cellulose- 29 perms, drywall- 49.74 perms; latex paint- 3.5-6.1 perms. . If required, a v.b. primer paint- .45 perms.

Read this on manufactured homes (mobile), interior v.b. and stopping exfiltration in Madison, WI.: http://www.fpl.fs.fed.us/documnts/pdf1993/burch93a.pdf

Compare these cities’s heating days to yours and the wall systems: http://www.buildingscience.com/docum...Insulation.pdf

“No, I did not add the VB primer to ceiling because the foam is my VB in this application. I need my ceiling drywall to breath into the living space. Do you see any issues that I should be concerned with using this method?” ----------- 1’ of SPF is only 1.8 perms (semi-permeable) . Double that, and ½ the perms = 2”of foam is 0.9 perms (semi-impermeable), barely a vapor retarder- (1 perm, by most standards) A good read: http://www.buildingscience.com/docum...gs?full_view=1

Be safe, Gary

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discdog

I'd love to hear your story about how your plan worked out.