On 10/5/2010 1:03 PM, wrote:

Bingo. And that is 75% of the reason you have a moisture barrier.
Having attended more than one cementitious product installation
instructional seminar they all agree to that. That is also why they
STRONGLY recommend a suitable paint over the siding.

With our weather extremes, I am gunshy about installing Hardie on long
unbroken runs. Tough to beat on areas that are just a couple of
pieces (or less) wide, but long runs don't seem to be a good fit with
our weather. I have mitigated the problem of the product expanding
and contracting somewhat by using good quality paint to prime the
backside before installation on the longer runs. Shorter runs still
receive nothing.

I have gone to houses that we clad with cement planking a few years
ago, and in long runs (say 40 - 50' across a house) that stuff moves
like crazy even after a factory rep certified our proper installation
(at the request of the client).

Which leads to the second reason for a "moisture barrier". Slip
sheathing. When you nail off the siding directly onto the wood
(sheathing or studs) it creates enough friction that when the siding
moves it will tear up the connection points. (See Leon's post on the
wallowed out holes further down). The barrier allows the cement
siding to "slip" a bit around the fasteners since it is not directly
nailed to hard contact the wood. Since movement can/will cause
spalling and thus loose siding, why take any kind of chance? I
can't. I have to warrant my product.

That is why on a shed or an open shop we just use 15# or 30# felt.
Works great, and cheap, too.

30# please ...

Your above is why I use "vent skin" construction on a house finished
with siding products, particularly in our "hot, humid climate" building
zone.

By layer, as follows: sheathing; 30# felt (or tyvek); vertical 1x4's @
16" OC installed thru/to soffit/attic floor; siding nailed to 1x4's.

(Note: I don't like to blind nail cement board using this method and
would rather putty nail holes prior to painting.)

The resultant 3/4" gap between the sheathing and siding from first
course all the way into atic (with a 9" screen folded over 1x4's at the
bottom to keep out insects"), PLUS ridge vent(s), will insure a
continuous flow of air moving up the sides of the structure and out the
roof vent.

Any moisture that does penetrate the siding will be mitigated by said
air flow, which keeps thing dry over the long haul.

An excellent construction method where high wind and rain is expected.

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www.e-woodshop.net
Last update: 4/15/2010
KarlC@ (the obvious)