Ok so I am going through the details here and my choices for lap siding here in Chicago area are basically LP Smartside or Hardie. The LP Smartside installation says to use furring and put foam BETWEEN the furring, not on top, so the wall the siding is nailed to is flush (no rainscreen). This prevents waviness in the installed siding due to twists in the furring strip faces once screwed down. So I am curious, for you guys running rainscreen applications with the 3/4 airgap, do you guys use Smartside or Hardie? How do you prevent/minimize the waviness?

Hardie looks fine on 16" o.c. 1x furring in most applications.

If 1x furring through-screwed 24" o.c. through thick foam layers there can be some bowing of the furring between fasteners- people who insist on ultra-flat walls can use 2x furring.

"twists in the furring strip faces once screwed down."
this has not been a problem in my installations with any siding

Yea I'm leaning Hardie at this point obviously. So you're saying affix the FURRING with fasteners at 16in oc ? Got it...

Posted By Surfsup on 21 Jan 2014 04:49 PM
Yea I'm leaning Hardie at this point obviously. So you're saying affix the FURRING with fasteners at 16in oc ? Got it...

No, fix the furring through-screwed to the studs with fasteners 24" o.c..  I was presuming 16" o.c. stud spacing.

But even with 24" o.c. studs, pancake-head timber screws on a 24" grid are PLENTY of fastener for fiber-cement siding at up to 5" of foam.  This guy is an old hand at it- take his and others' detailed recommendations to heart and you'll get there without any trouble.   Be sure to use pancake heads, not anything smaller and definitely not bugle heads, which are guaranteed to split the furring over time. Make the timber-screws long enough for 1.5" penetration into the stud, not just the structural sheathing.  Don't try to re-invent this wheel, and don't take short cuts- this is a well trodden path at this point.

Dana and Bob thanks. The studs are going to be 16in oc. Ok I will affix the furring with screws at 24in oc. The fasteners I was going to get were these: 4-1/2" HeadLOK FMHLGM412-250

These are flat-head screws. 4.5in because I figure 0.75 for furring, 1.5in for foam, 0.5 for sheathing = 2.75in and 4.5-2.75 = 1.75" penetration into the stud. I used the James Hardie "formula" to come up with this. I believe these screws were also recommended by name, as well. Your links give me a "access denied" error...FYI.

Building science advisor website is having problems with that ACCESS DENIED mesaage & are trying to fix it. sometimes repeated tries will get in, othertimes not.

So a question about the furring, is kiln dried 1x4 better than OSB sheets ripped down to 4 inches wide?

the 1x4 will be straighter.

I think whether it's kiln dired or green is less important.

ok I'll stick with the KD...thanks

1 x 4 will split and warp, osb or plywood will remain straight. Also you can rip sheet goods to wider then 3.5" if you need to, for around windows and corners.

Remember you are creating a space that will collect moisture and move it away so you can expect the strapping to go through many moisture content changes. Engineered products normally stay straighter through these cycles.

@Surfsup
I'm in the design phase of designing my first home to build for me and my wife.

I am planning on using Hardie Artisan lap siding which is 5/8" thick and less likely warp and bend creating waves in the siding. That is as long as the surface is Flat and stays that way. The home exterior wall constructed will be a high performance wall system with exterior ridged foam insulation and furring strips for the siding attachment.

Some of the Problems I see with furring over EPS

1. Furring strips over soft sheathing has a possibility of being forced/pushed down the shaft of the Screw collapsing the sheathing which would cause waves in the walls lap siding.
2. Problems also could occur as Dana1 stated bowing of the furring from the expansion and contraction of 1x wood furring strips and sliding down the shaft of screw compressing the sheathing.

This is the best solution I could think of to help solve some of the problems as listed above.
Found a Building Science Corporation article discussing the technique.

http://www.buildingscience.com/docu...spray-foam


For residential construction I would say you could solve the problems partly by using plastic sleeves as spacers at each end of furring strips and every other screw from there on. It will open up a hole behind the furring strip down into the foam. But this could be solve by adding silicon calk inside the sleeve before installing each screw.  It would add more cost to job but would solve a few of the problems with concerning furring strips over foam.

Another possible outcome by using a sleeve is you could shim the furring strip outward with a longer sleeve to straighten out the wall section which is bowed in.

As for using kiln dried wood I would think it would be a waist of money ...... I would rather it have a slightly high moisture content when I attached it so it would be more likely to contract rather than expand once the cladding is installed. Either way the Kiln dried wood will adjust to the surrounding environment.





Would like to find a Timber Screw configured similar to the one below.
Better yet, threaded all the way up the shaft, I think this would be a good enough alternative and easier solution for residential wood framing construction than using the sleeve spacer!

I went on the hunt looking for a continuous threaded Timber Screw but no luck ..... ANYONE?

FBBP, That's what I thought...so I will go back to using OSB. I would think plywood would not be as durable long-term as OSB?

ricky005, thanks for the article. I think I will just bore a counterbore into the furring at each screw and monitor each screw
s pressure to make sure they don't compress the furring as best as possible. There is very little siding on the front of my house. I am more concerned with the long-lasting of the siding, which is why the rainscreen is being installed, not necessarily it being perfectly non-wavy. I'll see if I can find those screws though. I think they will be expensive.

My general understanding was that plywood is MORE durable than osb. At least in terms of water tolerance. I believe it was in a conference where Joe Lstiburek listed materials in order or water tolerance, highest to lowest (lumber, plywood, OSB, particle board). Maybe your have are thinking of durability in another way, so i might be off base (dimensional stability maybe). The metal hat channel or c-channel could be more/less durable/ dimensionally stable depending on the circumstances.

Another thread here recently mentioned an easy fix for keeping siding straight (at least at the time of installation). Overdrive the screws fixing the furring to the studs, then selectively loosen them until they are straight, hanging a straight edge on the wall was used as a guide in the example i believe.

I was thinking about using a 4 foot level and just put it against the furring strip to check it

Posted By Surfsup on 06 Feb 2014 05:36 PM
I was thinking about using a 4 foot level and just put it against the furring strip to check it

4 Foot or greater straight edge, the longer the better.  Me I would prefer 6 foot plus a string level pulled from outside corner of building to opposing side to double check the furring strips before calling it finished.

P.S.
Had no luck finding fully threaded timber screws .... Maybe someone should contact a manufacture and make them aware of the durability enhancements it would make for wood framed homes when attaching Furring strips over ridged insulation.

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