[Greenbuilding] wall envelope - rainscreen

[JOHN SALMEN]

I have an inspector insisting on full 25mm embedment for a fastener so full
1x3 or include it in my eng. schedule which is fine but onerous. Problem
here is standard furring is fir, generally not well graded, and splits far
too much - I'm just not comfortable with that - this is seismic area and
only so much staggering you can do on a 1x3. Ply battens are an option - but
I'm really looking at a different assembly for the bulk of the walls.

Since we are looking at render finishes (I have to say I like them for the
coast - we seem to be getting much heavier rain periods alternating with
sun) I'm comfortable with the foam as a substrate cladding)and putting the
capillary break at the wrb at the sheathed structural wall. Nice stable wall
for a good wrb and flashing details and the gap seems to provide some
additional potential drying of the wall.

I know wufi (the lbnl version) can't model ventilation flow but the airspace
did provide in the model for lower moisture content in the sheathing. I also
modelled it in therm looking at condensation in the assembly. Like I said
though I don't have practical experience of this assembly - but I do like
the notion of providing some drying potential at that point in the assembly

John
 

JOHN SALMEN ENVIRONMENTAL DESIGN
4465 UPHILL RD,. DUNCAN, B.C.  CANADA, V9L 6M7
PH 250 748 7672 FAX 250 748 7612 CELL 250 246 8541
terrain at shaw.ca

-----Original Message-----
From: John Straube [mailto:jfstraube at gmail.com] 
Sent: October 16, 2010 2:22 PM
To: JOHN SALMEN
Cc: Alan Abrams; greenbuilding at lists.bioenergylists.org
Subject: Re: [Greenbuilding] wall envelope - rainscreen

Raindrop GreenGuard does help drain, but I dont know if it will resist water
well. At least it is not perforated like GreenGauard which DOES let water
through. I love their DC14 Drainage board though Dupont DrainWrap is one
product which I have tested and we have used on numerous projects very
successfully.
The code says 1" for supporting siding, which is actually 1" nominal, which
means a dressed 1x3" works.
This 1x3 furring has been used to attach cladding of all types in hundreds
of thousands of buildings, so attaching stucco lath or vinyl or fibercement
or wood clapboard to 1x3 (nominal) is not even a hint of a problem.
Attaching 1x3 to studs behind foam by using screws at 12" to 16" vertically
on center has been done in many thousands of home.  
We, and many others, have built hundreds of homes and now dozens of
retrofits (that I know of, many more are likely being done) with 4-12"
screws through foam to the studs.
Yet, John you say, "So for 3" of exterior foam you need to fasten 1" battens
with a min. 5" fastener thru to the framing - and then secure cladding to
that with full 1" depth fasteners. Basically gets unworkable."
This is not unworkable. You either have not tried to do it, or you have done
something wrong.
We and others have done this in California, Alaska, Kansas, Massachusetts,
Ontario etc etc. Eg all corners or North America.  I have done it
personally, and we have had contractors do it given only the most basic of
instructions.