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Old 02-12-2018, 03:24 PM   #1
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Vapour barrier / insulation


Hi,

I'm finishing a room in my basement that has two exterior walls. I've got 1-inch Foamular polystyrene rigid foam right on the concrete block, tuck-taped and sealed with spray foam.

I've then got my 2x4 frame and was planning to put fibreglass batt insulation in between the studs.

Is a polyethylene vapour barrier required/recommended in this case?

As well, what kind of insulation method is recommended for the rim joists? Is a vapour barrier required there too? If so, what's the preferred method?

Thanks,

- H

P.S. I'm in Southern Ontario, Canada
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Old 02-12-2018, 03:36 PM   #2
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Re: Vapour barrier / insulation


"Required" I cannot answer for you but current thought is no vapor barrier on below-ground walls so they can dry to the inside.
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Old 02-12-2018, 03:37 PM   #3
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Re: Vapour barrier / insulation


You may have to check with your local code authority to see if the Foamular meets their requirements for a VB or if the poly is needed as well. in the states i could advise but Canada is hanging onto the VB requirement last I heard.

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Old 02-12-2018, 06:18 PM   #4
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Re: Vapour barrier / insulation


......bump.......
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Old 02-13-2018, 02:16 PM   #5
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Re: Vapour barrier / insulation


Having trouble getting an answer from the Building Code reps, but the consensus I seem to be seeing is that since 1” rigid foam actually passes more water vapour (1.1 perm) than the commonly accepted definition of a vapour retarder (1.0 perm), it does not create a vapour barrier. I would then still need the poly vapour barrier on the warm side. Does that make sense?

I'm also leaning toward the Rockwool/Roxul batts instead of regular fibreglass between the studs. Seems like they're more water resistant if (but hopefully not) any moisture does get in there. Thoughts?
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Old 02-13-2018, 02:39 PM   #6
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Re: Vapour barrier / insulation


Foam is not a vapor barrier, it is only a vapor retarder. 1" may not be thick enough for your climate as the goal is to create a thermal barrier to prevent condensation from forming.
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Old 02-13-2018, 02:44 PM   #7
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Re: Vapour barrier / insulation


If you never have a leak the only moisture you have to worry about is in the house air.
If it finds it's way past an electric out let or under the bottom plate and around the insulation moisture condenses on cold surface. We see old insulation with dirty spots or sides all the time which indicates the pass that warm dirty air was traveling.
I have not seen any proof that stopping that air at the wall hurts anything.
So I will hang on my belief in vapour barrier.
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Old 02-14-2018, 07:15 PM   #8
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Re: Vapour barrier / insulation


my dad lives in northern Michigan and he glued that rigid foam board right to his unsealed poured concrete walls and now he has a huge mold problem in his basement
he did not build any other walls just the foam on concrete
personally I think if he would have sealed the raw concrete he would have better off ( not sure ) NOTE the basement walls were sealed on the outside of the walls so no water leaking from outside just the moisture in the air mostly in the spring/summer

just my 2 cents
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Old 02-14-2018, 08:50 PM   #9
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Re: Vapour barrier / insulation


Hi pm, where is this mold forming, on the surface of the rigid insulation or behind it? And it it near the top or bottom?

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Old 02-15-2018, 04:30 PM   #10
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Re: Vapour barrier / insulation


[QUOTE=Bud9051;5163785]Hi pm, where is this mold forming, on the surface of the rigid insulation or behind it? And it it near the top or bottom?

its on the concrete behind the FB from floor to ceiling, its black mold but we are not sure its thee '' black mold '' but I can tell you that the smell of his house will cling to your clothes and anything you bring into the house, we have been trying to get him to take care of it but he is at that point in his life that he says heck with it its us kids problem ......now I am no expert but I believe that if he had sealed the concrete he might had been better off but I still think you need some kind of air circulation between the concrete and the wall or a better idea would be to put the foam board on the outside, the guy next door to me is building a new house and he used those foam blocks that you fill the middle with concrete so the wall is like 20'' thick it a sweet deal.....don't help on a old house ....... good luck with your project.....
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Old 02-15-2018, 04:47 PM   #11
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Re: Vapour barrier / insulation


There is a lot we don't know about this installation, but many basements have been insulated with rigid insulation against the foundation. The recommendation is to keep it tight and apply the adhesive in a horizontal pattern to limit any air circulation between the concrete and the rigid foam. Sealing the foundation has proven to only reduce the moisture flow but not eliminate it. The objective is to allow the moisture to pass through the foam board, but that means no foil or plastic facing. Any vapor blocking and even a tiny flow of moisture will accumulate and create a potential problem.

Was there a water issue before the foam was installed?
How thick is the foam?
Does the foam have a foil or plastic facing?
Was the basement wall painted?

Not healthy to leave it as it is as much of the air inside a home comes through the basement in winter.

Bud
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Old 02-15-2018, 05:38 PM   #12
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Re: Vapour barrier / insulation


it is the pink FB I think it is an 1in. thick so no foil, there was no paint applied to the concrete just liquid nails to hold the FB to the concrete. this mold is on all four walls and there has been no water leaks, he did paint the FB but not the side facing the concrete.
my dad thinks it has to do with the grade does not come to the top of the concrete foundation, there is about 2' from grade to bottom of house siding and he has seen frost in the winter on the north wall but that's not often, if he ran a dehumidifier more it might help
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Old 02-15-2018, 06:21 PM   #13
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Re: Vapour barrier / insulation


Quote:
Originally Posted by pigman#1 View Post
it is the pink FB I think it is an 1in. thick so no foil, there was no paint applied to the concrete just liquid nails to hold the FB to the concrete. this mold is on all four walls and there has been no water leaks, he did paint the FB but not the side facing the concrete.
my dad thinks it has to do with the grade does not come to the top of the concrete foundation, there is about 2' from grade to bottom of house siding and he has seen frost in the winter on the north wall but that's not often, if he ran a dehumidifier more it might help
If you don't have enough insulation, warm moist air can condense on a cold surface. Mold spores are everywhere all you need after that is food like dust or other organic substance that will feed the mold.
If he has black mold now, it should all be redone.
Tape a piece of poly on the surface and if water accumulates on the outside of that you know it is a humidity problem in the basement and there is not enough insulation.
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Old 02-15-2018, 07:21 PM   #14
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Re: Vapour barrier / insulation


I don't have the answer but I'll add some thoughts.

1. I don't believe the grade outside is affecting this problem. Typically the grade should not be closer than 6" from the siding and certainly not all the way to the top.

2. Seeing frost at the top is normal with very cold walls and warm inside air. That is the purpose of the rigid, to provide a warmer inside surface. Since your mold situation is behind the rigid i don't think the moisture is coming through the insulation.

3. Painting the rigid may have contributed to moisture accumulating behind the rigid. All paints, some more than others, act as a vapor retarder. That in conjunction with the limited permeability of 1" of pink may have blocked whatever moisture vapor was moving through the wall. Note, most concrete suffers from moisture vapor issues. Sealing the outside doesn't stop it.

5. I agree with Neal that the mold should be properly cleaned up. Don't just rip the foam off of the walls as it will flood the air with mold spores. Seek professional advice for remediation.

6. Remember, internet advice can come from many sources and cannot/should not be used as the final word, even my advice. It is getting harder and harder to know what is right and what is wrong.

Bud
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