Should I use Tyvek or tar paper on basement walls?

Question

We are going to be redoing our basement which was done in the 60's and very cold. We have been told to apply Tyvek or tar paper to the walls, stud, then vapour barrier and drywall. We plan on using fiberglass batt insulation because of costs (we are retired and limited income). We would love to do the spray foam and not have to worry about all the vapour barrier and such but we are out of budget - Styrofoams seems like a lot of work by the time you have to cut each piece.

We are going to get some prices by contractors but want to do some work ourselves to keep costs down so of course the behind the scene work is what we want to do - i.e. studding (16 inch on centre and insulating and maybe installing the drywall but not taping and finishing). If we use tar paper, do we just overlap it or do we tape it much like you do the seams of Tyvek? Do we go right to the floor with the paper or, like with the insulation, do we keep it a foot off the ground? Any help, suggestions are greatly appreciated.

Answer 1

"Should I use Tyvek or tar paper on basement walls?"

Neither. No building paper or wrap against the foundation. Just use foam it is not really all that difficult to cut.

The best practice really is to use rigid foam against the foundation wall, then a framed (possibly insulated) wall with drywall and no vapour barrier.

Batt insulation in the framed wall is debatable. Green Building Advisor has articles that say it's not a good idea because it can absorb moisture, but others sources have no problems with it. If you do use it (I would if you are in a cold climate and don't have existing moisture problems in your basement), I personally prefer mineral wool over fiberglass.

Don't forget about the cavity above the wall in the joist spaces.

Trusted Sources (read them!)

• Built Wrong From the Start (Fine Homebuilding) [PDF]
• Basement Insulation for all climates (Building Science Corporation) [PDF]
• How To Insulate a Basement Wall (Green Building Advisor)

Good Luck!

Answer 2

The main concern with vapor barriers and fiberglass insulation is preventing condensation and trapped moisture in the insulation that could result in mold and mildew. The vapor barrier on the conditioned (heated) side of the wall is there to prevent warm moist air from passing into the insulation and condensing on the cooler side. If you install a vapor barrier on both sides, moisture can become trapped inside the insulation and result in mold/mildew.

Tar paper is water proof and could easily act like a second vapor barrier. When used on a roof, there are typically soffit and ridge vents to keep the underside of the roof dry, rather than trapping moisture in the attic. However, on your basement wall, there doesn't appear to be anything that would allow trapped moisture to escape.

Tyvek and other house wraps are different in that they block liquid water, but not water vapor in the air, from passing through. This allows the walls to breath and prevents trapped moisture.

Therefore, in your situation, a house wrap product is probably best to prevent damage from any moisture in the walls from getting absorbed by the insulation and wood framing. Where the framing meets the floor, I'd be tempted to use either a vapor barrier, a foam weather stripping (it comes in a roll and is the width of the framing), and/or pressure treated lumber with nails designed for pressure treated framing.