house wrap for unfinished space

My house was build in 1972 and has tar paper behind T111 siding. I am in the process of building out some previously uninhabited space (basement area under the garage) and have noticed that the tar paper does not extend to this area. This is not surprising as the space was previously empty. I am relunctant to insulate and sheetrock without addressing the weatherproofing issue. Do I need to rip off the T111 and house wrap or tar paper behind the new siding or can I wrap the existing T111 with something and then apply some kind of siding--- maybe cedar shingles, directly over the wrap? I admit that I am not familiar all that knowledgeable about construction but it seems to me that if I wrapped the T111 and then shingled that would adequate. No? Wouldn't the existing T111 serve as the sheathing in this case?

I am not sure of the situation you are describing. Do you have a walk out basement?

You can wrap the T111 with something like Tyvek and then put on a siding of your preference. The T111 is simply the sheathing which goes on before the wrap. Look on Tyvek's website for instructions on wrapping after windows are installed.

Jason

Vapor Barrier Inside

Condensation moves from the heated to the unheated side. If you are going to heat the area, you want a good vapor barrier inside the insulation.

House wraps typically let water vapor through, but stop liquid water and air infiltration. They are not typically a vapor barrier (even tar paper breaths a little). Somewhere in the last 6-months or so, Fine Homebuilding had an article on housewraps. After all of the engineered housewraps he evaluated, he said he preferred tar paper...fwiw.

water barrier

finnegan said:

I am not sure of the situation you are describing. Do you have a walk out basement?

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The garage sticks out over a hillside but is not merely standing on on stilts, it is is held up by cripple walls. The space I am converting is the hollow under the garage. I just built a floor over the hill in the empty space. The cripple walls have T111 siding on them but no tar paper or vapor barrier. At first I thought I should take the siding off, put tar paper on the outside of the studs and then put the siding back up. But the siding is worn out so I decided to update by adding cedar shingles--- a popular look in the San Francisco bay area these days. In this case I would just use the T111 as sheathing, wrap the vapor barrier around the building as it stands and then add the shingles. Sound reasonable?

Your plan is fine as far as a weather barrier is concerned, but as Jad pointed out, vapor barriers serve one purpose and Tyvek type products serve another. If you like the T-111 and it is weather-tight, you can leave it alone and finish the interior space as you would any other space.

thanks

Thank you all for the help. I think I need to read a bit more on the difference between vapor barriers and weather barriers. It seemed simple at first but now I don't feel completely comfortable. I'll look at the articles you suggested.