Closed Cell Foam, plastic and air space?
I'm a semi-longtime reader and newbie to posting. And I need some help.
This is a general construction question, so I hope I'm posting in the right section. I'm going to help some relatives with drywall next month. They have an older, small, clapboard-sided house with no obvious housewrapping on the exterior. No path for air, unfortnuately. The clapboards were nailed to wood sheathing. The inside walls were plastered over lathe boards, with older blown in insulation (actually probably poured in insulation) on 2x4 walls. Location of house is in Catskill mountains, NY.
After removing the plaster and 2" lathe pieces, they had to shovel out wet and moldy insulation.
The plan is to hire a foamer to spray on closed cell foam to a depth of 3 or 3-1/2". Next they will glue and staple on 5-6mil plastic on the end of studs. After that, the 2" lathe strips will be mounted on the studs vertcially to create an extra 2" of space. 2" strips will be put on the top and bottom plates.
After that comes the drywall.
Questions I have are: 1. Will the closed cell foam act as a water barrier for the outside? 2. Is there a chance that the 5-6 mil plastic act as a secondary moisture barrier? 3. Is there any reason to use the plastic? 4. Will the plastic stop outgassing smell?
They don't want to pay the extra to foam out the additional 2" (lathe strips). Residing the exterior isn't an option for quite some time due to cost.
Any ideas, comments, questions are welcome.
Questions I have are:
1. Will the closed cell foam act as a water barrier for the outside?
Well yes after water has penetrated the clapboard and sheeting, where the benefit? Make sure the clapboard is tight and detailed.
2. Is there a chance that the 5-6 mil plastic act as a secondary moisture barrier? The vapor barrier has been and on again off again issue in the industry. Your foam will act as a barrier but check with local codes for requirements.
3. Is there any reason to use the plastic? No.
4. Will the plastic stop out gassing smell? Check with the manufacture for outgassing for their particular material. 100's of different foam formulations out there
Thanks for your answers. What about sliding some faced fiberglass insulation in that 2" cavity? Would that be a good idea. Or unfaced? I was thinking of getting some R-13 and splitting in half.
Huge job here, but is there any way to remove the siding, install a WRB (Tyvek, etc), spacing, then put the siding back on? It sounds like you are going to get wet again, as mentioned above, so what is the point to re-insulating? And, no, there is no need for poly inside w/ closed cell foam. Why the inside space? A chase for elect and plumbing? Sure, insulate it after you're done if you care to; even fiberglass will help somewhat.
With a wood material like clapboard I would think you need an airspace. Could you add an airspace to the back of the wood sheathing? Then you would only have to remove the top and bottom of the exterior clapboards to cut openings to the vent space.
Why not apply your 2" lathe to the studs before you spray, and then you could get additional depth of sprayfoam? I see no reason for the inside airspace, unless it is a electrical chase. Splitting batts in half also sounds like a waste of time.
As others mentioned, the poly vapour barrier is not needed as the sprayfoam acts as a vapour barrier.
shazapple and jklingle,
Thanks for your comments. They don't want to foam out the entire 6" (5-1/2") because of the big ramp in costs from the foaming contractor. And it would be very difficult to add proper airspace without re-siding the house. They know this should be done, but the cost associated with doing it (taking off clapboard, wrapping and re-installing) is very prohibitive right now.
The spacing isn't as a chase, just extra room. All of the moulding, etc are set at that distance.
Which Zone are you in: http://resourcecenter.pnl.gov/cocoon...s/full/973.jpg
Compare the annual heating degree days mentioned in the first part of this article to yours: http://www.buildingscience.com/docum...nd-wall-design
Notice that no poly required if in Zone 5. You could use a paper-faced vapor retarder in Zone 6, or Certainteed's Membrain in either as it is self-adjustable, similar to paper-faced (variable perms) asphalt-coated.
You will get thermal convective loops if leaving the cavities empty or a poor fiberglass installation- pp.45-47: http://www.buildingscienceconsulting...Measure_Up.pdf
Studs are R-1.25 per inch. Figure your whole wall R-value after subbing your foam's R: http://www.coloradoenergy.org/procor...f/r-values.htm
Only big problem is the studs will be cold constantly, when they should be warm with foamboard outboard instead of in cavity to prevent condensation, again- no poly, notice especially "Flash & batt", similar to you, less risk; http://www.greenbuildingadvisor.com/...foam-sheathing
Use ADA: http://www.buildingscience.com/docum...wall-approach/
Stop the air leaks! Electrical outlets, etc. Air leaks vs. diffusion, Fig. 4: http://www.buildingscience.com/docum...researchreport
Thanks for your posts. I can't get to the one link, but from what I can read, I have a few more questions.
First off, It appears that the house is in Zone6. And, the heating degree days is around 7200, so that would make it borderline Zone 5/Zone 6, which I guess should mean plan for Zone6?
Could your "paper faced retarder" be paperfaced insulation? Based on not leaving an empty cavity, I guess batt insulation is needed.... so the question about paper insulation.
Looks like and R value of ~23.5.
Doing foamboard outside insulation is a great idea, but just not practical, in terms of time and cost.
Drywall and air leak information noted... Thanks.
But reading through some of the docs you referenced, it seems like this situation needs to keep the vapor retarders on the inside,
page 6 and Figure 5
Does that mean the faced insulation?
Thanks for your help!
Yes, paper-faced insulation batts, "Ginger vs Mary-Ann; http://www.buildingscience.com/docum...024-vocabulary
Quick update: The foam expanded to (close) the total depth. We ripped apart R13 insulation and finshed the job. Hung drywall, and things seem to be okay. Now we need to do the second half of the house.
Thanks for your help!!
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