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Old 12-10-2009, 08:42 AM   #1
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Poly over insulation?


We just added an addition and have a valted ceiling 3/12 pitch. We insulated with kraft faced insulation but then covered the insulation with 4mil clear poly, along with the exterior walls. We then installed pine T&G (car siding) over the poly.

I am now worried that we have "over" done it, in fact we may have caused more of a problem with moisture.

Am I correct and if so what should we do? Please help..... thanks.

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Old 12-10-2009, 10:19 AM   #2
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Poly over insulation?


Hey Jane,

The poly debate has been going on for decades. First homes were to loose, than to tight, ?????????. If you do some scientific study, you will find the amount of variables are extreme. You are dealing with weather related issues outside and air flow issues inside. They normally move toward each other and meet inside your wall.

If you have three teenage daughters who take extended hot showers, and forget to turn on the exhaust fan in the bathroom, assuming there is one, the water laden air will find a place to go, normally between the poly and the insulation.

In high humidity areas if you have an over sized central air unit it will run enough to cool the house but fail to remove the humidity. The cool humid air will find a place to rest.

Your situation is no different. At this point, understanding your specifics will help you control what you are able to.

A good article if you are interested?

http://www.ecohomemagazine.com/build...-barriers.aspx

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Old 12-10-2009, 10:53 AM   #3
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Poly over insulation?


"covered the insulation with 4mil clear poly, along with the exterior walls." ---- you must live in a cold or very cold climate or your building department requires this. I would have installed foam board on the rafters first to ensure a thermal break to the inside warm wood (and back primed). Hopefully you have 2" air space next to the roof deck with such a low pitched roof and continuous baffles with 1" space at ends.
http://www.southface.org/web/resourc...lings_4pdf.pdf
http://www.buildingscience.com/docum...on?full_view=1
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Old 12-10-2009, 10:58 AM   #4
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Poly over insulation?


Gosh; and there I was thinking you didn't even need insulation in Miami...or was it Montana...no wait, you said...uh....wait as minute! you didn't say. Hmmm...

Now how can we make an assessment of your needs when we don't even know where you live???
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Old 12-10-2009, 11:25 AM   #5
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Poly over insulation?


Sorry, yes you are right I would need to give more info. We live in Hudson, WI and yes we did install foam air space panels prior to the insulation. We also live in a log cabin home. The main house is full log the new addition was built with 2x6 framing and log siding on the exterior.
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Old 12-10-2009, 04:53 PM   #6
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Poly over insulation?


You should have an air exchanger in a "tight house." In older houses they are drafty enough to allow air to exchange moisture with the outside. There is nothing wrong with making houses more energy efficient, but you need to get the moisture out with an air exchanger, especially in a cold climate.
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Old 12-10-2009, 05:39 PM   #7
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Poly over insulation?


Quote:
Originally Posted by jane-diy View Post
We just added an addition and have a valted ceiling 3/12 pitch. We insulated with kraft faced insulation but then covered the insulation with 4mil clear poly, along with the exterior walls. We then installed pine T&G (car siding) over the poly.

I am now worried that we have "over" done it, in fact we may have caused more of a problem with moisture.

Am I correct and if so what should we do? Please help..... thanks.
You might want to speak to your local building inspector to see what code is in your area. We need a 6ml poly in British Columbia.

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Old 12-10-2009, 08:13 PM   #8
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Poly over insulation?


The drywall acts as an air barrier for the interior moisture trying to get out. Without it, or back priming, I would be concerned the condensation would rot the pine boards as it easily passes through the gaps in the t&g material.With the big gap between boards and the two or more nails per foot compromising your v.b., you may get wet insulation as well. Control the humidity as mentioned and did you install foam under the roof side of rafters? Did you leave a 1" gap between foam baffles for vapor to escape, as per manufacturer's directions? With the foam baffles, you install the additional Windblock (or rigid foam board) to prevent the cold outside air from washing and permeating the ends of the insulation at the wall/ceiling line: http://www.adoproducts.com/wind.html
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Old 12-10-2009, 08:26 PM   #9
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Poly over insulation?


If I understand correctly your question is: With both poly and the kraft facing creating essentially a double vapor barrier will you have problems.

Kraft facing and poly combined is not the recommend vapor barrier system, it's one or the other. But if you already have the T&G installed I would not worry to much if your ceiling is properly vented and insulated.
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Old 12-10-2009, 08:30 PM   #10
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Poly over insulation?


Doesn't anyone have inspections?

Anyway, jane, that is the way I did my addition. I am a Contractor in MN and had it inspected also. You did the right thing. The poly should have acoustic caulking on all openings(lights, outlets) and the remainder to the overlaps taped. You got at least R38 in the ceiling, right?

The reason I used craft faced was so I could staple it, in order to hold it there till I got the poly up. I have not had any problems.
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Old 12-10-2009, 08:34 PM   #11
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Poly over insulation?


Quote:
Originally Posted by MJW View Post
Doesn't anyone have inspections?
Not many remodels are inspected here in Wisconsin. They just want our money for permits, the rest they don't care about....lol
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Old 12-11-2009, 06:42 AM   #12
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Poly over insulation?


OK, I hope that by now - with all of these answers - everyone understands how important 'location' is to an assesment of insulation problems; I'd go further by saying that that is the #1 factor in all of this, not roofing, not insulation level, not type of insulation, not vapour barrier or retarder, not wall covering, baffles or airflow: all of those elements are pretty well dictated by 'location'...and to Mick from BC: it all depends on where in BC. 6mil poly vapour barriers are required in areas that are very cold - like the interior - but not necessarily in, say, Vancouver which is in a different zone.

So knowing that the OP is in WI, that puts you in a 'cold' zone, where recommended insulation levels for new construction are R38 in ceilings and R19 in walls, where air barriers and vapour retarders are a good idea. I don't know about code requirements or inspections in your area - those are local issues for your municipality...but beyond that, you say you have a log cabin.

Well, here moisture becomes an important aspect to manage seeing as how wood is hygroscopic, so proper roofing, soffits, flashing and downspouts are part of the overall picture. So starting with the roof, I would have insisited upon a rubber membrane on the roof to make sure the water doesn't penetrate, then I'd like to have the most ventilation I could have underneath the roof I would also have a vapour barrier or a good vapour and air retarder to keep the inside air from getting to the underside of the roof, and here I think you've done OK with the faced-kraft insulation and the poly.

Yes, putting up T&G pine will negate the vapour retarder by letting moist vapour into the insulation - but there you have the kraft paper...I don't see any mention of 'drywall' - where does that come in?
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Old 12-11-2009, 09:01 AM   #13
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Poly over insulation?


Quote:
Originally Posted by ccarlisle View Post
OK, I hope that by now - with all of these answers - everyone understands how important 'location' is to an assesment of insulation problems; I'd go further by saying that that is the #1 factor in all of this, not roofing, not insulation level, not type of insulation, not vapour barrier or retarder, not wall covering, baffles or airflow: all of those elements are pretty well dictated by 'location'...and to Mick from BC: it all depends on where in BC. 6mil poly vapour barriers are required in areas that are very cold - like the interior - but not necessarily in, say, Vancouver which is in a different zone.

So knowing that the OP is in WI, that puts you in a 'cold' zone, where recommended insulation levels for new construction are R38 in ceilings and R19 in walls, where air barriers and vapour retarders are a good idea. I don't know about code requirements or inspections in your area - those are local issues for your municipality...but beyond that, you say you have a log cabin.

Well, here moisture becomes an important aspect to manage seeing as how wood is hygroscopic, so proper roofing, soffits, flashing and downspouts are part of the overall picture. So starting with the roof, I would have insisited upon a rubber membrane on the roof to make sure the water doesn't penetrate, then I'd like to have the most ventilation I could have underneath the roof I would also have a vapour barrier or a good vapour and air retarder to keep the inside air from getting to the underside of the roof, and here I think you've done OK with the faced-kraft insulation and the poly.

Yes, putting up T&G pine will negate the vapour retarder by letting moist vapour into the insulation - but there you have the kraft paper...I don't see any mention of 'drywall' - where does that come in?

What?
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Old 12-11-2009, 09:03 AM   #14
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Poly over insulation?


We are not installing drywall but rather pine log siding on the interior as well to match the remaining interior. Also the final piece of trim has not been installed over the t&g at the ridge, Im wondering if I should cut the poly out at that point?

Thank you everyone for all your helpful answers. This is the first time I have ever posted anything on this site and I appreciate the assistance.
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Old 12-11-2009, 09:10 AM   #15
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Poly over insulation?


No don't cut the poly...a few nail holes here or there aren't going to force you into a second mortgage. And, yes I know you put t&g pine planks on the wall, but one respondent mentioned 'drywall' and I was trying to make the link.

MJW: what are you 'whatting"? is there something there that you don't agree with? if so, say so.

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