I'm installing 2 3/8" of Roxul Drainboard on the exterior of the house sheathing. Then 3/4" furring to support the wood siding 3/4"+ away from the Roxul.

Looking to use the long special-threaded GRK screws or similar to anchor in the framing. The vertical furring is 16" OC, just like the wall studs, so we'd anchor the GRKs through Ply sheathing and solidly into the studs.

Seems like the bottom of each vertical furring should have a block or solid stop. The foundation edge might have been good, but there's no available edge.

I was thinking about a block of some sort attached to the bottom plate for solid anchoring without blocking airflow

Thanks for any groovy ideas!

EDIT- This is LP Smartside going up

A good 5" -6" screw from GRK, Fastenall or Timberlok will hold the strapping well enough so that it will not "slip" on the wall. You should include an insect barrier at the bottom of the wall - typically roof venting material - either the roll vent type cut in half, or the solid plastic kind; either works to seal the gap between the strapping.

Thanks Bob-

The LP Smartside might be 1.5 pounds a square foot. Given the 16" OC vertical furring they require, I wonder what the vertical spacing of the screws should be? Any thoughts? 24"? 12"?

Interestingly, LP requires 1 3/8" nail penetration for the warranty. I'm tempted to say that's excessive and use 3/4" or 4/4" furring.

someone published a report of how many screws to use; I don't have a link, though, but two screws every 16" will be plenty. that length of nails appears to mean that they want the siding nailed through the sheathing into the studs, not the sheathing alone. (Wonder if they are worried about warping?) If you're not concerned about the warranty, using knotty pine strapping should hold the siding adequately. Personally I'd look for local pine clapboards if possible.

I'm going to be calling them tomorrow regarding these very issues.

I would LOVE to have used a local clapboard. I tried fast and furious, but no one cuts the bevel up here (N Michigan). So I ran outta time and didn't want to ship from VT

UPDATE:

LP isn't helping much. The siding attachment is purely your liability. They want lumber to lumber thermal bridging, not GRK screws through foam or Roxul. 2x4 furring, not 3/4". 16" OC, not 24". So at least according to the tech specialist I spoke with earlier, you can't get a warranty and avoid thermal bridging every 16".

Wood clapboard would be best if not for the price.

Posted By Bob I on 20 Apr 2014 08:15 PM
someone published a report of how many screws to use; I don't have a link, though, but two screws every 16" will be plenty. that length of nails appears to mean that they want the siding nailed through the sheathing into the studs, not the sheathing alone. (Wonder if they are worried about warping?) If you're not concerned about the warranty, using knotty pine strapping should hold the siding adequately. Personally I'd look for local pine clapboards if possible.

24" o.c. is what's specified in the FastenMaster's manual on the subject for insulation that thick. 

More here.

And here.

And here

This is exactly what I'm doing. Roxul Drainboard. 8 pound density. The article shows it works great. It would seem that 16" OC 1x4 vertical strapping / furring anchored with the special GRK-type screw at 16" would give the support and wind resistance. No squash blocks.

Somehow I'd feel better with a little shelf under each vertical strap, though.