At 07:50 AM 2/21/2000 EST, you wrote:
>>In a message dated 02/18/2000 3:23:35 PM Eastern Standard Time,
>>[log in to unmask] writes:
>>
>><< Among homebuilders there is a decided
>> retreat from housewraps and back toward #15 felt under claddings. >>
>
>Here's a related question:  We've been speccing traditional bitumen / felt
>dampproofing.  Our contractor prefers (of course) to use the newer poly
>whatevers.  I prefer the traditional, but he had a good point:  the bitumen
>will crack and dry out over time while the poly whatevers will remain
>resilient as long as they are not exposed to UV.  What do you think?
>
>
For above-grade applications-------

The bitumens become brittle over time mostly from heat (diffusion of
short-chain hydrocarbons). The stuff under decades-old siding tears easily,
but you can imagine it still acting as a weather barrier except where
movement has torn it. Where used over board sheathing it reduced the air
leakage for the building.

A builder on contract would want a wrap because it cuts the time down
considerably. A spec builder would have to consider the material cost. The
poly sheets should indeed stay good for decades. Tyvek and Rwrap are
polyethylene. The perforated wraps are polyethylene and polypropylene. It
was pointed out a few years ago that many vinyl sidings allow a lot of UV
through, which led to some reformulations, and that problem seems to have
gone away. The manufacturers seem to let you have about a month of exposure
before the cladding goes on. There may be an energy-savings argument for a
wrap overall, but I know of no "build-'em-tight" builders who rely on the
wrap for infiltration reduction.

I'd look at it this way: The failures will occur at a tear, or from reverse
shingling of a joint, or at a corner where a cut goes too far, or where
they try to finish the job at 4:30pm with not quite enough material up on
the scaffold. I'd ask the builders you deal with which product is most
likely to be installed carefully. That's a tossup in my view. There's a new
Tyvek that is "creped" (wrinkled vertically). It is used under the
Dupont-USG EIFS system (Oh no!!!). It has an application advantage in that
it is stretchable, so if a diagonal cut occurs, the material can be
stretched over itself and nailed in place.

You asked about foundation dampproofing. Might need a new thread on that one.