# Plastic on Interior Wall



## dogcom (May 23, 2009)

I know in Ontario and even across Canada they say seal the interior wall tight with plastic over the insulation. Living in Vancouver and having an older home I am not to sure I would want to do this because it seems to me it would rot your wall out.

When I renovated an area of my basement I put up the plastic but I slashed it so it would breath. I found when I sealed it tight a lot of water would build up behind the plastic so I slashed it. I heard builders in Vancouver have also done this after the inspector has gone through so the house won't rot out.

I think the wet coast may be different then the rest of Canada on this front.


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## OhGreatGuru (May 24, 2009)

Your question peaked my curiosity. i have little experience with building in BC, so I did a bit of looking on the net.

It is true that there is literature from warm humid climates in the US where they recommend against vapour barriers. But CDN publications do not agree for the BC coastal climate (whcih is cool & humid). There is a CMHC publication called Wood Frame Envelopes in The Coastal Climate of BC that you might find instructive. ( You can download it from the net) 

Among other things it says:
1. Codes may not require a vapour barrier in this climatic zone, but they still require an air barrier, and polyethylene is the most common material for this.

2. A damp wall will not dry effectively by air migration into the building, because the natural flow is exfiltration outwards.

3. Quote: *"It is important to note that the presence of polyethylene did not cause the moisture problems in the wall assemblies examined in the Survey, nor will its removal from wall assemblies prevent problems from occurring in the future."* This statement suggests that the real probem is walls that are not adequately designed or constructed to stop moisture from infiltrating from outside; and that contractors are attempting a cheap but ineffective fix by slashing the vapour barrier.


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## dogcom (May 23, 2009)

Thanks for the good reply ohgreatguru.

Actually after I slashed the plastic there was no more water forming at the top of the plastic or in other spots.

On point three you have a good point that moisture will slowly weep in and needs and exit. Old homes allow for an exit and new homes and condo's have been a huge problem in Vancouver as you have seen in the leaky condo crisis.


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## mind_business (Sep 24, 2011)

I'm not sure if slashing the vapour barrier was the right choice, unless you don't mind a drafty house. Have you considered installing an air exchanger?


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## Addy (Mar 12, 2010)

I know there were a lot of problems with people finishing their basement in new houses way before the concrete had time to cure... If I remember correctly it takes at least 1 year (maybe 2?) before the concrete is fully dry before you should finish your basement.

I've heard there's debate on this due to new building technology, but I'm curious why water would be coming in if the concrete foundation is dry and there is proper membrane on the outside? I've lived in Vancouver for the majority of my life so I'm aware of the issues there, but still when a proper membrane is installed there should be no issues.


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## dogcom (May 23, 2009)

It has always been an issue in Vancouver even after everything is dry. My wall was dry and it was summer when I put in tight and you could sure see the water forming in various areas of the plastic and it was wet at the top of the plastic.

On having a drafty house it has never been a problem for me because it never seems to get all that cold in the winter.


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## Addy (Mar 12, 2010)

dogcom said:


> It has always been an issue in Vancouver even after everything is dry. My wall was dry and it was summer when I put in tight and you could sure see the water forming in various areas of the plastic and it was wet at the top of the plastic.


Is there an exterior membrane as well? Our home in Vancouver used to have problems with moisture so we had a proper membrane put on and six years later it's still dry. I imagine the membrane will deteriorate over time, so time will tell how long it lasts.

I noticed a lot of 3/4 story condo units have or are in the process of ripping off the exterior wall and changing them over, so maybe it's newer technology than they had when the condos were built.

You should still have drafts in the house for air circulation anywhere you live. I'd say especially in Vancouver since it's prone to mold. We had vents installed - I don't know exactly how they work but apparently they exchange air without letting the moisture in. I wish I knew more about the technology, maybe someone else here knows better.


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## Lephturn (Aug 31, 2009)

I had this issue with my new home in one room in the basement. In this case I think the moisture was actually coming out of the studs. We sliced the vapour barrier and that let it dry and clean up. After a few months I patched and taped up the vapour barrier again and all was good. I think it was just wet wood used to stud it.

I also have an air exchanger that I use depending on the season and moisture levels in the house - as well as a good steam humidifier for the winter months. I am in Ottawa, so it's very dry in the depths of winter so I had to put in the humidifier to solve the opposite problem!

I suspect the house was moist the first year due to rain and snow getting to the frame before it was roof tight. It takes a long time for that amount of water to come out of the wood.


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## dogcom (May 23, 2009)

That is a scary thing lephturn even for people in Ontario who buy a new or newer home. In a sealed system if water is trapped in the wall you would get a terrarium effect where the water keeps recycling up and down the inside of the wall. You may not realize this is what is happening until significant damage is done.


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## Lephturn (Aug 31, 2009)

It was only for the first month or so in one small area - it's dry now. I've done enough work on the place to know for certain I don't have a problem at this point. After finishing the basement myself (and that's where the moisture was) I am confident it's fine now.

Actually where the moisture was is the electrical room and I didn't drywall it, so I can still monitor that wall.


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## londoncalling (Sep 17, 2011)

OhGreatGuru said:


> Quote: *"It is important to note that the presence of polyethylene did not cause the moisture problems in the wall assemblies examined in the Survey, nor will its removal from wall assemblies prevent problems from occurring in the future."* This statement suggests that the real probem is walls that are not adequately designed or constructed to stop moisture from infiltrating from outside; and that contractors are attempting a cheap but ineffective fix by slashing the vapour barrier.


This is 100% true. The National Building Code requires that all foundations be damp proofed to prevent the infiltration of moisture. Depending on the age of the home the exterior of the foundation walls may not have been damp-proofed thus allowing moisture to be absorbed into the basement and trapped by the .06mil poly vapour barrier. In areas of hydrostatic pressure(a high water table) the exterior must be waterproofed. This could also apply to the OP.

If I recall the appendix to the National Building Code of Canada has a diagram of various vapour barrier installations. However, like investing, unless you do your due diligence and research you are better off hiring a professional as the results can be disastrous.


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