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Gentlemen; In the process of replacing 3 windows I found out that behind the sheetrock ,there was no vapor barrier. Just unfaced insulation,2×4 framing with 1/2 in. plywood and (3) layers of 15# felt paper.yes 3 layers! underneath the masonite siding. My question is should i put in the poly? I will be replacing more windows and the time to do it will be then. where i tore the sheetrock down the insulation looked brand new,was built in 1975. I would prefer not having to tear down the rest of the sheetrock just to put in the poly ,but the area that i put the poly behind seems to be warmer than before.For some reason they put poly in all the ceilings but not the walls? Any comments?
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CMB
By "replacing" these windows do you mean that you didn't open up the wall, just removed windows and observed the no-poly phenomenon in the rough opening cavity? Or did you re-size/enlarge the previous window R/O's and cut into the ajoining stud bays?
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Patrick; I tore all the sheetrock off, slightly less than 1/4 of the house. Replaced a bow window with double hung and replaced a couple poor quality double hung windows. Straightened out the insulation stapled the poly up and sheetrocked. Do I really need the poly?
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C M B,
Where on the Planet are you?....climate-wise...
Jack : )
*The theory behind putting up a vapor barrier is to prevent interior water vapor from entering the wall and condensing. However, the theory has proven to be flawed in real world applications. The vapor barrier serves only to keep moisture trapped in walls, which causes rot. In short, I would not bother installing a vapor barrier. Kyle
*The latest politically correct terminolgy is Vapour Diffusion Retarder(VDR) and current theory on this board suggests that poly is not necessary if you have an 'air barrier' formed by drywall and paint. Go figure. You may have proven this theory correct with your own project's observations!! Ain't life. . . wonderful?
*I agree with Kyle. I believe that using poly as a vapor barrier only restricts the walls ability to"breathe". In climates of extreme changes in temperature I believe poly can create moisture andtrap it in the wall. If there is no apparent damage I would leave well enough alone. If you must use a vapor barrier, I would use a housewraplike tyvek which would not completely keep the walls from "breathing".
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Jack; Am from Maine,the northern portion. I think its a straight shot from Greenland to my back yard.
*For my own construction, I have gone to using 3/4" to 1" foil coated polyisocynurate (thermax) over the studs on the inside of the structure. This makes for interesting drywalling, but has resulted in a very snug and energy efficient building. The reflective properties of the foil seem to reflect radiant heat in in the winter and out in the summer. Now I am wondering if I will have problems with rot or the like in the walls. Any comments?
*For my own construction, I have gone to using 3/4" to 1" foil coated polyisocyanurate (thermax) over the studs on the inside of the structure. This makes for interesting drywalling, but has resulted in a very snug and energy efficient building. The reflective properties of the foil seem to reflect radiant heat in in the winter and out in the summer. Now I am wondering if I will have problems with rot or the like in the walls. Any comments?
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Dennis
I've used the same system in my own house. Why the worry about rot? Foil faced polyiso is an air barrier,( apparently even unfaced polyiso has a very low perm rating) tape the edges and no moisture can get through if you did a good job!!
reflectively
Patrick
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Yes, you will get lots of replies on this.
The replies you are getting so far are comparing apples to oranges. You have not given sufficient information for anyone to give an answer. Many more questions need to be asked first:
- Describe the complete wall system from inside to outside (material types and space dimensions), connections to sills and plates; etc.
- How is the space segregated/isolated from basement and attic (infiltration, exfiltration, stack effect and moisture control).
- How airtight and moisture proof is the rest of the place (from top to bottom)- from inside moisture (vapor) penetration and from outside bulk air and moisture penetration. What about the soffits, gable ends, roof connections, sill and foundation conections -- etc, etc.
- What kind of heating system are you using; fuel type; annual heating bill - do you care ?
- Whats the condition of the old insulation and framing - any signs of moisture or decay ? If so, on which sides of the materials - interior side or exterior side ? Adjacent to what other parts of the house ?
- What are you planning to do with the rest of the building; siding; housewrap; insulation; caulking; etc.
Check out Vapor Diffusion Barriers on the web; using gaskets, drywall and paint to do the job. But if the place is not air and moisture tight now and your happy with the operating costs and life of the materials, why do anything different ?
Getting into airtight building envelopes and controlled air exchanges using mechanical ventilation and energy recovery units is a whole new ball game. If your house was not built that way in the first place, you will use a lot of time and expense to retrofit it.
Examine the performance of your current materials and how they are put together -- put your question in the context of the whole house system. The answer to your question is yes, no, maybe, if, when, depends; etc ...
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The foil will work as a radiant barrier only if it is has an airspace of at least about 1/2". If anything is touching the foil, it won't work. 1X straping works well and may help with the drywall hanging.
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Gentlemen; In the process of replacing 3 windows I found out that behind the sheetrock ,there was no vapor barrier. Just unfaced insulation,2x4 framing with 1/2 in. plywood and (3) layers of 15# felt paper.yes 3 layers! underneath the masonite siding. My question is should i put in the poly? I will be replacing more windows and the time to do it will be then. where i tore the sheetrock down the insulation looked brand new,was built in 1975. I would prefer not having to tear down the rest of the sheetrock just to put in the poly ,but the area that i put the poly behind seems to be warmer than before.For some reason they put poly in all the ceilings but not the walls? Any comments?