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Aaron Easley
Vapor Barrier and basement

I am getting ready to finish my basement. The issue of vapor barrier has me up in the air. I have heard and read all kinds of things. Should I apply 6 mil plastic directly to the cinderblock with construction adhesive, then put the studs up, then used insulation with no batting? Should I use rigid foam? Please forward your suggestions.

reenieandrod
Re: Vapor Barrier and basement
Aaron Easley wrote:

I am getting ready to finish my basement. The issue of vapor barrier has me up in the air. I have heard and read all kinds of things. Should I apply 6 mil plastic directly to the cinderblock with construction adhesive, then put the studs up, then used insulation with no batting? Should I use rigid foam? Please forward your suggestions.

The best way to do this is to first install your new studded walls, making sure the sill plate is treated lumber, with the insulation blanket under the treated plate.

Mike Holmes, on "Holmes on Homes" did this to a house recently. He built the new wall against the concrete blocks, then used the blue, "closed cell" spray foam, which does not need a vapor barrior. The closed cell spray foam is much better than the open cell, plus gives better insulation quality. The spray foam is much better, becaue it will seal any little crook or cranny, to prevent any airflow. The spray foam is a little more expensive per square foot, but you will have no voids.

I wish I knew which episode he did this. Perhaps, if you go to the Holmes on Homes site, you might find it, because each episode is labeled. Do not use a plastic vapor over the concrete, because moisture will develop between the 6 mil and the concrete.

Besides TOH, Holmes on Holmes is another great program I watch all the time, for lots of great tips.

Good luck,

reenieandrod
Re: Vapor Barrier and basement
reenieandrod wrote:

The best way to do this is to first install your new studded walls, making sure the sill plate is treated lumber, with the insulation blanket under the treated plate.

Mike Holmes, on "Holmes on Homes" did this to a house recently. He built the new wall against the concrete blocks, then used the blue, "closed cell" spray foam, which does not need a vapor barrior. The closed cell spray foam is much better than the open cell, plus gives better insulation quality. The spray foam is much better, becaue it will seal any little crook or cranny, to prevent any airflow. The spray foam is a little more expensive per square foot, but you will have no voids.

I wish I knew which episode he did this. Perhaps, if you go to the Holmes on Homes site, you might find it, because each episode is labeled. Do not use a plastic vapor over the concrete, because moisture will develop between the 6 mil and the concrete.

Besides TOH, Holmes on Holmes is another great program I watch all the time, for lots of great tips.

Good luck,

Another note.........If you decide on fiberglas insulation to save money, use the 6 mil vapor barrior on the warm side, not against the concrete, like I mentioned above.

Re: Vapor Barrier and basement

Is there a reason behind doing this, reenieandrod?

reenieandrod
Re: Vapor Barrier and basement
rachael24 wrote:

Is there a reason behind doing this, reenieandrod?

Are you asking why to use plastic on the warm side? If so, I was assuming the owner might decide to forgo the spray foam and use fiberglas instead, when 6 mil plastic is needed. If using just the spray foam, NO 6 mil palstic is needed. Basement walls are always cold, so you want to keep out moisture and drafts.

Sorry for the misunderstanding.

canuk
Re: Vapor Barrier and basement

The first thing to consider .... issues with moisture penetration from the basement (foundation) walls.... if so ..... that needs to be properly addressed first.

If the foundation walls are clear from any issues .... another method you may consider ....... try using 2 inch rigid foam sheet insulation.

You could attach the foam sheets using an adhesive that's formulated for the foam .... if you use the wrong type it will ruin the foam sheets.

Attach the sheets of foam to the foundation walls first .... completely covering the walls.... making sure to seal the joints with a house wrap tape.

This will eliminate the need for the vapor barrier preventing the warmer moist air from the living space from contacting the cold foundation wall surface.

Then put up your framing studs and finish as desired. .... and if you wish to add batt insulation into the stud bays .... no problem.

Having the foam sheets completely covering the foundation and behind the studs will improve the insulating performance by providing a continuous thermo break.

Just a thought. :)

reenieandrod
Re: Vapor Barrier and basement
canuk wrote:

The first thing to consider .... issues with moisture penetration from the basement (foundation) walls.... if so ..... that needs to be properly addressed first.

If the foundation walls are clear from any issues .... another method you may consider ....... try using 2 inch rigid foam sheet insulation.

You could attach the foam sheets using an adhesive that's formulated for the foam .... if you use the wrong type it will ruin the foam sheets.

Attach the sheets of foam to the foundation walls first .... completely covering the walls.... making sure to seal the joints with a house wrap tape.

This will eliminate the need for the vapor barrier preventing the warmer moist air from the living space from contacting the cold foundation wall surface.

Then put up your framing studs and finish as desired. .... and if you wish to add batt insulation into the stud bays .... no problem.

Having the foam sheets completely covering the foundation and behind the studs will improve the insulating performance by providing a continuous thermo break.

Just a thought. :)

Very, very good suggestion. I agree with this 100%.

jjlucas
Re: Vapor Barrier and basement

I'm doing a similar project, trying to frame and drywall over poured concrete walls. However my basement walls have several obstacles like water pipes. Also, I'm only finishing half of the space. (The rest will remain with bare / painted concrete).

So if I attempted to do a plastic sheet vapor barrier or sheet insulation w/ tape for a vapor barrier - I'd never get a complete seal. Would there be any value in these methods, knowing that the seal is imperfect?

What would you think of skipping the vapor barrier entirely and just leaving a 1 inch gap between the poured concrete and the studs / insulation?

(Additional info: Prior to this project, the walls in the partially finished half were top half painted concrete, bottom half wood paneling. The wood paneling had been there for ~30 yrs with no musty smell or signs of mold when it was removed - so there is not much moisture coming in from the concrete.)

Mastercarpentry
Re: Vapor Barrier and basement

Go with the sheets as canuk indicated, then fill any untaped gaps with minimal-expanding spray-foam to flush. That's all the sealing you'll need or get without 'making a boat' out of the basement.

Phil

jjlucas
Re: Vapor Barrier and basement
Mastercarpentry wrote:

Go with the sheets as canuk indicated, then fill any untaped gaps with minimal-expanding spray-foam to flush. That's all the sealing you'll need or get without 'making a boat' out of the basement.

Phil

Thanks! sounds like a good plan.

Question - why do you recommend minimal expanding spray foam? I would have thought that the expansion would help seal. But then I've never worked with spray foam before.

jjlucas
Re: Vapor Barrier and basement
canuk wrote:

.... try using 2 inch rigid foam sheet insulation...This will eliminate the need for the vapor barrier preventing the warmer moist air from the living space from contacting the cold foundation wall surface

Canuk -

I like your approach, but I have two concerns related to my specific situation:
(1) I'm only finishing half of the basement, i.e. half of the exterior walls. Would that interfere with the barrier? I'm thinking that I could use the construction tape to seal the edge where the finished part ends. Thoughts?

(2) My walls are not totally flat - it is poured concrete and there are 0.5" raised ridges every 4 feet or so. Will that interfere with the barrier? I suppose I could try to line up board seams with the ridges and fill with spray foam. Thoughts?

Thanks!

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