Exterior wall sheathing plus…
GBA Editor
| Posted in General Questions on
Plywood is a fine exterior structural sheathing, providing bracing. but it is essentially non permeable.
If moving moisture through the wall is essential what do you advise in place of plywood…. Perhaps old style diagonally applied 1″ boarding…. ??
Is there a plywood product which is micro perforated so that it breathes while providing strength.? If not, someone ought to make it.
You might address the fact that some builders are applying ice and water shield over an entire roof to avoid leaks….I think this is a disaster waiting to happen especially in older houses….
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Replies
Don,
Of course, diagonal board sheathing is an excellent approach. Here in Vermont, rough boards are cheaper than plywood, although more labor-intensive to install.
In Canada, some builders have indeed experimented with drilling holes in plywood sheathing. Of course, the holes undermine the air tightness of the wall assembly.
A roof that is completely covered with Ice & Water Shield can work, as long as the roof assembly is able to dry to the interior.
Martin H...
Thanks for your response....I don't
t know what size holes Canadian builders have been experimenting with in plywood, but the spaces between diagonal sheathing boards are fair size... If that works I don't see why drilled plywood wouldn't.... On the other hand sheathing boards themselves are permeable. ( and they do provide good nail holding ability when applying siding and less formaldehyde.).. Ah...the good old days.
Donald,
I agree that we are using too many impermeable materials to enclose our homes. I am in the minority in this position, but I also believe we are going to discover in 10 or 20 years that bituthane covered assemblies will lead to unanticipated consequences.
Additionally, there are many reasons to consider locally-sawn rough lumber to be far more "green" than any manufactured sheet stock. Less processing and embodied energy. Lower transportation costs. More breathable and hygroscopic. No chemical additives or outgassing. Easily recyclable, waste easily repurposed as firewood...
I thought the idea was to build a tighter envelope? Build a home that leaks less air through the walls. I use 9' and 10' OSB panels and I install them vertically. I run a single panel from the top plate to the bottom plate. Check out these guys http://www.tallwallosb.com
Summit County, CO requires full bituthane roof covering by code. It's usually accompanied with a vented attic, so no worries there.
In a conditioned attic, or over a cathedral ceiling, yes, it could lead to trouble.
I have used a product called Panelvent when I was in the UK three years back. Is there a similar product here? Just Google panelvent for the details.
you could move the structural sheathing to the interior face of framing. this has been utilized on a number of passivhaus projects.