[Greenbuilding] Insulation Fasteners

[RT]

(George wrote :

> I'm about to screw through 4-1/2" of polyiso, I can only find 6" screws 
> affordably ($13/100ea), longer screws are $1ea

Many moons ago in my mis-spent yoot as a carp-ender, I remember building  
an Alex Wade [spit] design for a fellow who came seeking our  
timber-framing expertise.

Wade's [spit] plans for the shell called for 2x6 girts [stoopit idea],  
with XPS sheathing and 4x8 sheets of compressed sawdust/glue siding that  
had lines pressed into it to make it look like tongue & groove.

That building left me with such a bad taste in my mouth I never built  
another foamed-plastic outsulated stick frame ever again. (I also remember  
exclaiming to an order desk clerk at the fastener supply regarding the  
price of the long stainless steel threaded fasteners : "At that price, do  
you have a +%@*#^ pimp handling them ???"

But enough harping on the Past.

Thinking now about the issue of the pricey long screws for attaching thick  
outsulation where Z-channels aren't an option...

Presumably one would install a sheet metal channel or angle flashing at  
the bottom edge to provide an ant/termite/rodent barrier ?

That should suffice to temporarily support the sheets of foam against  
gravity until they can be fastened to the framing. No ?

For holding the foam against the framing how about something like the  
brick ties that are used for foam-wrapped steel studs where the brick tie  
wraps around the backside of the stud ?

The "ties" in this case I think could simply be a piece of U-shaped  
annealed wire (say somewhere between 10 and 14 gauge as a WAG ?) poked  
through foam from the backside of the wall, stapled to the back of the  
stud if necessary. Maybe the bracing wire used for farm fencing would do  
the trick. Sold in bazillion-foot-long cpils and cheap like borscht. (It  
may be too heavy though).

The "U-ties" could be easily fabricated on-site borrowing a technique from  
the electronics assembly industry where they'd hold a bunch of the wire  
legs of resistors in the jaws of some long needle-nose pliers and bend  
them all at once to get identical bends .

For the U-ties instead of needle-nose pliers it'd probably be a matter of  
clamping a $#!+-load of wires (cut to the same length and ends aligned)  
between two 2x4s and them folding the protruding wires en masse.

Furring strips (to which the siding would be attached) could be  
pre-drilled for the U-ties (while the lumber is still stacked/banded in  
bundles).

The protruding legs of the U-ties would simply be twisted (like lashing  
re-bar) until the furring and foam is pulled sufficiently tight against  
the framing -- the furring serving as a spreader to prevent the two legs  
of the wire from pinching towards each other and cutting into the foam.

The top ends of the furring strips could be clipped to a nailer attached  
to the underside of the rafters to prevent them from sagging.

If the lump of wire from twisting/being bent over is a problem, a quick  
pass with plunge router to make a shallow (say 1/8" ?) mortise at each of  
the pairs of pre-drilled holes shouldn't be too much of a chore.

No doubt there would be some other fine-grain details to work out but the  
idea seems not too whacked-out enough to be workable.
-- 
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

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