Plastic sheeting inside/outside

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  #1  
Old 04-01-05, 09:28 AM
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Plastic sheeting inside/outside

I'm remodeling and insulating (previously uninsulated) home.

I'm planning on installing plastic sheeting over insulation (of couse paper side facing heated area).

I thought it was supposed to be stapled over the insulation (between insulation and future sheetrock).

Building inspector say Under insulation (between planking and insulation).

He doesn't do sheetrock inspections so he wouldn't know which way it was installed.

Which way is right???
 
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  #2  
Old 04-02-05, 07:50 AM
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Plastic

This is the order to install. Studs, insulation, plastic if you want to. The Inspector was correct in that the plastic is usually put on before sheeting is put on your exterior walls. You are past that stage. You are using backed insulation. This is good. I am not a great one for putting plastic over paper backed insulation, because when the plastic sweats, the moiture has no where to go but into the sheetrock. Good Luck
 
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Old 04-02-05, 08:07 AM
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We put a poly V/B over all paper backed insulation. That is stapled in the studs so it dont make a bump in the wall. This way you have a full and tight V/B over the whole wall studs and all no holes. We let it over the windows at this time till trim outalso . Saves a lot on clean up. Now on the ceiling we put it up there also. If you have paper backed up there ok .If not and your going to blow it in later and its still cold out. Dont mud the drywall in till you get the insulation up there first.

ED
 
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Old 04-02-05, 08:21 AM
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Okay so the order is..

Paperbacked insulation (paper facing interior) then plastic between insulation and sheetrock.

I've never heard of it going under insulation - but I haven't been around construction that long either.

House was newly sided, with new sheeting (insulation boards) put in place.
 
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Old 04-02-05, 08:37 AM
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Building inspector say Under insulation (between planking and insulation).

You know is he new at this??? Could be he is thinking of the house wrap Tyvek. that he would see in many new home now.

ED
 
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Old 04-02-05, 08:45 AM
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plastic inside out

No he's not new - isn't that scary?? I was offered the job, but felt I didn't have the experience required....I guess that didn't stop him though!

He was trying to convince me that firestops weren't important (extra work) and plastic Had to be under insulation.

He's offered some bad advice in the past - I always go with an independent (read highly paid) professional inspector when purchasing. So far he's saved me about $60,000 by finding "powder post beetle" infestation (that when from plate, right through to wood flooring on first floor). This in a home that inspector said just needed a little TLC.

The new regulations in PA concerning building inspectors has this guy retiring early (when he's no longer granfathered).

It's scary to think that he's not the only pro out there offering bad advice the difference is he has the power to insist it be done his way.

He doesn't inspect my houses (I almost hit him with a "dropped" hammer when he came to check my new roof- oops!). I go with outside underwriters (electrical) and again paid inspectors. This way I feel that I'm doing my best to offer safe well constructed units.
 
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Old 04-13-05, 07:04 PM
dave61
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vapor barrier 101

Kathie, the conventional wisdom on vapor barriers says there should be only one in a wall. So if you are stapling kraft faced fibreglas batts to the studs, you already have one (although not a great one). If you then put up plastic on the inside such as 4 or 6 mil polyethylene, you have a second V.B. That's not good because moisture can be trapped between the two and may start rotting the kraft paper, then it's down the slippery slope from there...I would either 1. use faced batts and skip the poly or 2. use unfaced batts and cover with poly.

It's OK to use an air barrier (such as Tyvek) on the outside of the insulation because it's not a vapor barrier. Its function is to pass moisture but retard air flow.

dave
 
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Old 04-14-05, 06:58 AM
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Plastic sheeting VB

My brother installs sheetrock for a living (I wish he lived closer) and I asked him about the plastic over paper backed insulation. He's been using it on his own properties for over 30 years and says he has never had a problem.

He says his heating bills are at least 25% less then houses of comparable size.
 
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Old 04-14-05, 07:26 AM
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dave61 Im with kathie659 all the way. Ill go back more, for 40 years that I have been used a poly V/B in homes basements and earth contact homes. Over the paper back insulation. Been back in many and have had no trouble at all in any of them.

ED
 
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Old 04-14-05, 08:36 AM
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http://www.eere.energy.gov/consumeri...heets/bd4.html

This page discusses vapor and air barriers and their applications. Though not really discussed thoroughly, "Thermal-Moisture Dynamics" explicitly implies that condensation occurs when the temperature of the heat drops to "Dew Point". This is highly unlikely to occur before the heat enters the insulation. As the heat traverses the insulation it does drop in temperature and if there is a sufficient amount of moisture traversing with the heat and the temperature of the heat reaches Dew Point, condensation will occur. Vapor barriers retard this flow of moisture, hence reducing the probability that condensation will occur even when Dew Point temperature is reached. In other words, applying plastic sheeting over faced insulation is not a concern with condensation. In fact, it is common practice among professionals.

25% savings is somewhat over-optimistic. The true purpose of the plastic sheeting is to act as an "Air Barrier". Vapor barriers deal primarily with heat transported moisture as described above and air barriers deal primarily with air transported moisture. Though air infiltration and leakage are being addressed with the use of air barriers and there are a lot of factors involved, this application is clearly misunderstood by most people and even professionals.

It is unhealthy not to allow fresh air into and inside air out of the house. The primary source of this air exchange during the winter is the heating then cooling of the air inside the house. For example, when you blow air into a balloon, it gets bigger and when you let air out of it, it gets smaller. It is also true that when you heat air, it expands and when that same air cools, it contracts. The house cannot get bigger or smaller with the expansion and contraction of the air inside the house during the winter.

Air Barriers purpose is to control where the air exchange occurs within the structure. Though it may reduce the amount of air exchange, it does not seek to stop it. For example, let's say you meticulously staple the faced insulation to the studs of the wall. It is still not air tight. If you apply plastic over the faced insulation, even poorly attached, it is considerably more air tight than the stapling of the faced insulation. Since air just like water or electricity, seeks the path of least resistance, the plastic sheeting creates the resistance needed for the expansion and contraction of the air to occur elswhere in the house. In other words, there is a much higher probability that the heated expanded air in the house will enter the wall cavity without the plastic sheeting than a wall with one. And heated inside your wall cavity that has insulation will produce condensation during the winter.

Though it has been well documented that reducing air infiltration and leakage saves energy and lowers bills, this particular application has more to do with preserving the structural integrity of the house and the health and well-being of the occupants of the dwelling than it has to do with energy conservation.

Francis R. Lazaro
Energy Conservationist
 
  #11  
Old 04-14-05, 09:04 AM
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plastic sheeting

My mistake - he never claimed the entire savings was due to sheeting.

We discussed air flow, insulation and various heating/cooling systems....it was just his observation that by incorporating several energy saving systems into his home, he was able to save substantially on heat & cooling costs.

Prior to new sheeting/ siding & insulation, the house I'm renovating had an enormous amount of air movement in the walls- I opened a small hole to fish wiring through and it actually felt like a fan blowing in there (kind of a pulsing movement of air). THe condition of the plaster wasn't bad, but given the lack of insulation and extreme (to me) air movement, I opted to remove all walls.

House is about 3/5 done and the comfort level has greatly increased and even before the spring "warm up" I noticed the furnace running much less.
 
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Old 04-14-05, 09:47 AM
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I opened a small hole to fish wiring through and it actually felt like a fan blowing in there (kind of a pulsing movement of air).
Thats why code here calls for all wire holes or other holes in walls to be sealed top and bottom with foam.

ED
 
  #13  
Old 04-14-05, 12:06 PM
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Plastic sheeting VB

I thought that type of air movement would be fairly unusual - have you come across that before? Perhaps the weather conditions were right to feel the air flow, but this is the 5th house I've ripped out and I never noticed anything like it before.

I was doing some preliminary "fishing" to save a few bucks in labor - electrician actually ran the wiring. (Didn't give me much of a break for finding him paths through walls/floors though )
 
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