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Rich-out-West
 
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MikeP wrote:

As noted above, trapping moisture between the sheathing and
housewrap/felt-paper/siding in not good.

If water is running down between the siding and sheathing it is
best to stop the water from getting behind the siding. ..... Water
should not be able to get behind the siding!!

The first priority should be preventing water from getting behind
the siding. Housewrap/felt behind the siding is a secondary line
of defense.


We should be careful with the wording here... The notion that water
cannot get behind properly installed siding has been shown though
exhaustive research to be false. It stems from thinking only in terms
water draining due to gravity, while overlooking factors like wind
driven rain, condensation, capillary action, and leaky window
assemblies. There is literally no siding product in common use that
does not get water behind it. This includes wood, fiber cement, and
other bevel sidings, stucco, brick, metal, and vinyl. Wide eves and
proper siding installation of course minimize water intrusion, but
won't eliminate it completely. For more information on this subject
visit www.buildingscience.com or look for articles by Joe Lstiburek and
others in all the common construction journals.
IMO, knowing what we now know, the only prudent plan is to install
siding over furing or plastic mesh to create a drainiage plain and
promote ventilation. This is what's commonly refered to as a
rainscreen wall. For new construction, it adds only a few hundred
dollars to a typical siding installation. The benefits include longer
life for both siding and finishes, and much less chance of structural
rot and/or mold. In Washington State, many of the larger production
builders have started to baseline rainscreen construction, perhaps out
of fear of mold litigation.
Even in a partial retrofit application like the OP is facing there
are options. I've seen at least one housewrap (GreenGuard) that
incorporates thick fiber bands to create a minimal drainiage plain
between the siding and sheathing. I'm not sure this would be as
effective as the 1/4"-3/8" space typical of furing or mesh
installations, but it would certainly be better than nothing. I've
seen quite a few houses going up in my area using this product, so I'd
imagine it's not much more than ordinary housewrap.

Richard Johnson PE
Camano Island, WA