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Does anyone have an appreciable history with installation of horizontal vinyl siding over furring strips, attached through several inches of rigid foam to studs?

user-1115477 | Posted in Green Building Techniques on

I am referring to a general wall assembly with several inches of rigid foam over studs, followed by 1-by or ripped 3/4″ ply furring strips attached with headlok screws into studs, say on 16 in. centers–so that there are voids, or vented, areas between strips. How does the siding installation hold up if installed over such strips? Is it good to make the strips wider than, say, 4 inches so the vented areas are less and support for the vinyl is more? Certainteed vinyl siding installation instructions seem to be against this vented approach, but at the same time their website points to a technical bulletin from Fastenmaster that certainly supports the furring strip approach-so they are confusing.

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  1. jhrockwell | | #1


    This web site is loaded with good information about the system you describe. Here is a start:

    Also, there are lots of articles available for downloading via Fine Homebuilding, Building Science Corporation et al. Good luck.

  2. GBA Editor
    Martin Holladay | | #2

    In addition to the link provided by John, check out this article: How to Install Rigid Foam Sheathing.

  3. user-1115477 | | #3

    John and Martin, thanks very much for your quick responses. Unfortunately, my questions were not addressed by any of the articles cited or otherwise. I have been very closely familiar with Martin's articles since the time they were written, and actually familiar with the subject matter before those articles appeared. Also, I have looked at Fine Homebuilding and BSC. My questions are not about how to apply foam, wrb, furring strips, nor about structural integrity and holding power of furring strips. I have an entire house sitting right now with furring strips all over it, applied, I believe,correctly, with headlok screws.

    My questions are specifically about VINYL SIDING applied over such an assembly. Additionally, there is no concern with the strength of attachment of vinyl siding onto the furring strips on 16 in. centers. The concern is whether or not the void, the venting area, between furring strips presents a problem for the lasting integrity of a vinyl siding installation. There is a potential degree of freedom for vinyl siding movement or bending because of the "vents" that would not normally be there with a conventional installation that provides a continuous, solid surface (ply, osb, or 1 in. continuous foam).

  4. GBA Editor
    Martin Holladay | | #4

    The Vinyl Siding Institute recognizes the use of furring strips under vinyl siding. Check out the Vinyl Siding Installation Manual.

    The manual has several references to the use of furring strips, including this one: "Screw fasteners can be used if the screws do not restrict the normal expansion and contraction movement of the vinyl siding panel on the wall. Screws must be centered in the slot with approximately 1/32” (0.8mm) space between the screw head and the vinyl. Screws must be able to penetrate not less than 3/4” (19mm) into framing or furring."

    Installing vinyl siding over furring strips is very common, especially over concrete blocks (CMUs). See the illustrations below from the manual I linked to. (The two illustrations have blended together. Click the lower illustration to enlarge it.)

  5. user-1115477 | | #5

    Martin, much thanks for giving me that reassurance. Time after time you give good answers.

    I had actually printed out the Vinyl Siding Installation Manual from the institute some time ago, and saw what you posted, but had forgotten.

    It's easy to have forgotten such a low-key, mild, positive position on the furring strips when my recent readings have been stronger against their use. A Certainteed representative told me on the phone that the furring strips are fine, but to fill in the gaps between with 3/4 in. insulation, to end up with a continuous, planar surface. The Certainteed installation manual states things like:
    --"Vinyl siding must be applied over a rigid SHEATHING that provides a smooth, flat surface."(p. 21, emphasis added)
    --The manual discusses use of furring strips to correct an uneven wall surface, and then notes: "Note: You must apply rigid sheathing over the furring strips." (p. 22)
    --"Never install vinyl siding over open furring strips or studs." (p.72)

    Despite the mixed positions, my guess is that Certainteed (and others) just don't want to extend themselves beyond acceptance of anything short of a "perfect" substrate. But I'm sure someone has installed vinyl siding over the furring strips, and has probably experienced good results, if the other important installation details were followed. That is why I asked for comment from someone who has previously done it. I can't be the first---was never first at anything else!

  6. GBA Editor
    Martin Holladay | | #6

    Well, there are advantages of following manufacturers' instructions. If CertainTeed won't allow it, I would find a vinyl siding manufacturer that will allow it -- in case you have a future warranty claim.

  7. user-1115477 | | #7

    OK, well, almost good answers time after time. There's no vinyl siding manufacturer that would officially "allow" it.

  8. GBA Editor
    Martin Holladay | | #8

    OK, I've learned something. I assume they allow the use of furring strips as long as the gaps between the furring strips are filled with 3/4-inch-thick rigid foam -- am I correct?

  9. user-1115477 | | #9


    I can find no manufacturer's installation instructions that specifically mentions vinyl siding installation over open (3/4-inch-deep vent) furring strips as an approved method.

    As far as "they" (Certainteed) are concerned, there is no telling what they officially "allow," from my experience. I've already mentioned what the Certainteed installation instructions say, but they are not definitive, especially since they cite the Fastenmaster document. Even the statement from the manual that I previously mentioned, "Never install vinyl siding over open furring strips or studs," is given in the vertical siding section of the instructions, and I don't think that statement is given in the horizontal section.

    The Certainteed installation manual does NOT say it is ok to use furring strips as long as the gaps between are filled with 3/4-inch-thick rigid foam. It doesn't mention that at all, to my knowledge. That statement came from one of the 3 different Certainteed phone reps I have called. The phone reps were all over the place on the issue of Certainteed horizontal siding applied over open (vented) 3/4" furring strips installed 16 in. o.c., rigidly attached to studs, and coplanar, as follows:

    Phone rep #1 did not know, in the end, and transferred me to an expert at Certainteed headquarters. I got the expert"s answering machine and he never called me back.

    Phone rep #2 didn't see a problem with installation using the furring strips (too easy, there, so I was suspicious)

    Phone rep #3 was the one who said it is ok to use the furring strips, but fill in between with 3/4" rigid foam.

    So the phone reps don't seem very official to me, to represent what is allowed by Certainteed.

    It seems odd that GBA for years has been promoting the furring strip approach to be used under "cladding," but that there does not seem to be any history with vinyl siding as the cladding. Yes, I recognize that some people don't support vinyl at all.

  10. GBA Editor
    Martin Holladay | | #10

    Mastic Vinyl Siding (a division of Alcoa) has an installation guide that shows furring strips with rigid foam between the furring strips. Surprisingly, the illustration depicts rigid foam than is not as thick as the furring strips.

    Here's the link:
    Mastic Vinyl Siding Surface Preparation

  11. user-1115477 | | #11

    Yes, this issue gets more suprising (scarier) all the time, even beyond my disbelief that it really doesn't seem to have been encountered or addressed before.

    Like you say, the Mastic illustration is suprising (scary), not only because it shows foam thinner than the furring, but because the link also states, "Fill in the area between the furring strips with insulation boards to make the wall level." Level? Presummably, they mean to establish a coplanar mounting surface for the siding, at the same time that they illustrate shallow voids, instead.

    I guess I could go back all around the house and fill in 3/4 inch-thick foam, negating all the vents and screens already and installed and wow..............

    OK, I'm thoroughly perplexed but, Martin, thank you for sticking with me some.

  12. TrQhFS6ysA | | #12

    On furring strips, is it best to use 1x4 or plywood strips. What would be best over time?

  13. GBA Editor
    Martin Holladay | | #13

    There's nothing wrong with 1x4s -- and they are available in long lengths. I certainly wouldn't bother to run plywood through a table saw to make furring strips.

  14. GBA Editor
    Martin Holladay | | #14

    I think "coplanar" is a pretty long word for the technical team at Mastic Vinyl Siding. "Level" is easier to spell, even if they aren't quite sure what it means.

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