Proper vapor barrier installation.


Old 02-15-07, 04:42 AM
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Proper vapor barrier installation.

HELP!!! I'm wondering if someone can help me determine the proper way to install a vapor barrier. I've just recently begun refinishing my basement; even though I've never experienced any water or moisture problems I chose to seal the walls and floor with DryLok just as a precaution. Now I plan to install 2x furring strips along the walls and put up 1 1/2" extruded foam insulation, tape all seams and caulk all joints. Then I will frame the walls with 2 x 4's and insulate with fiberglass batts.
My confusion comes with the installation (if one is needed at all) of the vapor barrier. Some things I have read state to install the vapor barrier closest to the warmest side of the room directly under the drywall. Others say to install the plastic along the concrete walls. Which is correct? Wouldn't the installation of the DryLok and rigid foam essentially be a vapor barrier? And should I use fiberglass insulation that has a paper facing or not in conjunction with a plastic vapor barrier? Sorry this question is so long but I want to make sure I do the right thing. Thanks.

Last edited by DIY_Tim; 02-15-07 at 10:36 AM. Reason: as a catalyst for inviting response; correct typo
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Old 02-15-07, 02:00 PM
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The foam is the vapor barrier - tape all the seams of it and make sure it is continuous - it works extremely well. Put it tight to the concrete wall - you can use the strapping to hold it or the wall framing... You want the basement to be able to dry to the inside.
Old 02-15-07, 03:15 PM
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Proper vapor barrier installation.

There is no such thing as an absolute vapor barrier.

What kind of foam? - Who ever said every foam is a vapor barrier?

A vapor barrier is an arbitrary definition. Some people say a 4 mil poly is not, but magically a 6 mil is? - What if you have a 6 or 10 mil with nails?

You can properly have double vapor barriers if one is a certain percentage less that the other.

The reason there are so many opinions on vapor barrier applications is because there are many different climates and conditions, different home configurations AND people with EXPERT opinions. An expert method from someone 500 or 1000 miles south or north of you is only an opinion.

The proven method - Look in your own neighborhood for similar homes that have successful basement finishing projects. Talk to the owners and find out how it was finished. That is the proof.

P.S. - If you do not insulate and install the appropriate vapor barrier in the ENTIRE basement, it does not make much difference what you do with the finished area if you have air circulating behind your finished walls unless your treat your finished area as an island with insulated interior walls.

Old 02-16-07, 09:32 AM
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My take on the first post was that 'extruded foam insulation' was meant to imply XPS, if it wasn't that's still what I meant by foam.

Dick, basements tend to be more of less universal fortunately. Above ground and it really varies by geographical area.

BTW, the intent of my post was that the strapping not be on the wall first. You don't want convection happening there.
Old 02-16-07, 11:14 AM
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First of all, I would not put furring strips on the wall. Why invite moisture penetration of a wall that you said you have no moisture problems with by punching holes in it with masonry fasteners.

Either glue the rigid foam to the foundation wall with an approved adhesive or attach the foam to the back of your 2x4 wall.

When I did my basement, I built the walls on the floor, covered them with 1/2 foil faced foam board, taped the joint with foil tape and them propped up the walls so the foam board was up against the foundation wall. I live in MD so I didn't feel the need to use a thicker foam board because cold snaps don't last more than a couple of weeks here, even in the dead of winter, but if you want to use 1 1/2" foam there is no harm in that

I then used kraft faced R-13 in the stud cavities and finished with dry wall.

As in your situation, I never had moisture problems in my basement (most likely because when I built my house I was absolutely certain exterior water infiltration barrier and drains were properly installed), but I think you could employ this method above and be just fine.

As you have mentioned, there is universal disagreement on where to put the vapor barrier and as you have seen differing opinions on how to complete a simple project.

Good Luck.
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