Vinyl Siding Over Furring Strips
A Q&A post wonders whether vinyl siding should be installed over furring strips. Although some builders apparently do so, advice from manufacturers seems contradictory.Image Credit: Image #1: Carol Collins
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Wall assemblies that incorporate rigid foam insulation over exterior sheathing, followed by furring strips and siding, are becoming common. The extra layer of insulation helps reduce thermal bridging through wood framing, and the furring strips create a ventilation space behind the siding that promotes drying.
But writing in a Q&A post at Green Building Advisor, Sonny Chatum wonders whether this wall system, often called a “vented rainscreen,” is compatible with vinyl siding.
“I am referring to a general wall assembly with several inches of rigid foam over studs, followed by 1-by or ripped 3/4-in. plywood furring strips attached with HeadLOK screws into studs, say on 16 in. centers — so that there are voids, or vented, areas between strips,” Chatum says. “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.”
It’s an intriguing question that could potentially affect many builders and homeowners. Is it OK or not?
Industry group seems to back idea
Several posts direct Chatum to online articles about the correct way of attaching furring strips to the wall over a layer of foam, but it is the vinyl siding itself rather than the furring strips that has Chatum concerned.
Specifically, he wonders whether the void behind the siding between the furring “presents a problem for the lasting integrity of a vinyl siding installation.”
On this question, GBA senior editor Martin Holladay offers a link to a Vinyl Siding Institute installation guide that…
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16 Comments
pre-notched furring strips.
You can get furring strips pre notched into eps. You will probably want a wrb over the foam so you just have to be careful that your nailing ino the strips through the paper. then simply apply the viynl siding like a regular job. This is perfect for viynl but i would'nt do fiber cement this way.
ICF
we build mostly ICF homes 30 - 40% have viynl siding
vert straping 16" oc 12 years + and have seen no problems so far
personaly i wouldnt use viynl on a dog house but customors choice
Siding by myself with the furring already in place-steel siding?
Scott, thanks for following up, and there's still questions, as you note. Over the years, it seems that GBA has strongly supported the furring strip approach, but perhaps has been somewhat casual about the implications of specific cladding types applied this way. I sort-of quietly felt that GBA "owed" us readers a more in-depth look at the situation. One question is, do you have any history of success/failure with the vinyl job shown in the picture you used?
Thanks, Randy R., for the 12 yrs. of experience. So, in your experience, none of the vinyl has taken on a wavy appearance because of any vinly sinking into the spaces? What cladding over furring strips do you use the most? I live in the dog house that I think I'm going to put vinyl on. I should be able to install vinyl all by myself, which is one reason I "like" it. Furring is already on, and the Alpha B. is biting at the fur, so I'm looking for a comfort zone.
For now, I've started filling between furring strips with 3/4" foam, because I just don't trust the vinyl not to get wavy over the open areas. Look closer at the Mastic instructions that Martin cited
(http://www.mastic.com/Homeowner/Learning_Center/Install_Instructions/Installation_Instructions.aspx), page 17: "Do not apply vinyl siding directly to furring strips without sheathing, because the siding may conform around the furred areas causing an uneven appearance." That would be cute--it might "catch on."
I know it's more expensive, but does anyone want to talk experiences with steel siding? Can I do it myself (assuming competency)? The Rollex instruction manual shows an installer going right at it with installing the steel siding over furring strips.
doghouse
never had a problem with wavy siding as long as the plane of the straping is true
the siding should remain nice and strait the 1/2 " bend on the butt should hold its shape
as for straping i rip 5/8 or 3/4 whatevers on sale presure treated plywood into 3 inch strips
i have found plain staping cups and warps and throws out the wall
(word of caution dont use iron or galvinized screews with pt lumber)
stainless steal is the best fastener or ceramic coated
Furing under vinyl
What timing. I just decided to do vinyl over strapping. I was thinking that would reduce the amount of nail holes through the 2" iso over the sheathing. I was looking at this product (http://www.alside.com/index.aspx?page=54) as it has a reinforcement strip. Just a bit of insurance against sagging. Each 8' fur strip will be attached with three screws. The siding nails will pierce the exterior aluminum skin on the iso but not the interior skin. Please comment before I start cutting checks!
Vinyl Siding can be purchased
Vinyl Siding can be purchased that has a foam backer, and is superstiff. Of course it is meant to be tight to sheathing and part of the insulation package. It is by far the best looking vinyl. And it is as expensive as all other choices such as fibercement or cedar, etc.
A home with lots of exterior foam is expensive to build. So, one might as well upgrade one's siding choice to a top shelf product. To save costs if really needed go with T 1-11 which done right can look great.
struggling with same questions
Great timing on this discussion for me also since I am currently trying to decide what to do with vinyl/foam. I am only trying to cut down of thermal bridging for my 2x6 construction heated garage and wanted to do 1" polyiso but now know that is not enough to keep dew point outside wall... I contacted Mastic vinyl company to find out if I could nailor screw thru 1-3/8 polyiso with regular vinyl OR if I could nail their insulated siding thru 1" of foam.....I have recieved no respose.
I am so undecided at this pointthat I am considering attaching the foam to the interior of the wall. I did this on my home several years ago and have beeen happy with it. If anyone has any links to interior foam discussion it would be much appreciated.
My concerns about strapping over foam are more due to it warping and the fact that I did not figure. the foam/strapping into my overhang design (too late now and I dont want to lose any.
vinyl siding handbook say max thickness foam under vinyl is 1".
Wondering what all posters above did with housewrap (WRB). under foam. over foam or ommited completely.
vinyl over strapping
Firstly, good luck with trying to get any guidance from the vinyl manufacturers. I have tried and get pretty much the same response as mentioned above. For them it seems, it's caveat emptor and CYA.
We have done several vinyl siding jobs over foam with strapping with no problems (none yet anyway). The most recent was 2" of Thermax over pine board sheathing. After stripping the original wood siding, we wrapped the house with tyvek, taping all seams. We did this mostly to protect the house from the elements during the ridgid foam installation process. Over the tyvek, we attached 2" of ridgid foam using occasional 3" roofing nails and roofing tins. We would later be installing vertical strapping 16" oc, so we didn't go overboard with the roofers and tins. All foam seams were taped with aluminum tape.
On the outside corners we "strapped" with 8" wide rips of 3/4 plywood to give good nailing for the 6" vinyl corner boards. In the field, and around all windows, we just ran standard drywall strapping. All strapping was attached with 4" GRK screws. Since the sheathing was 1" pine boards, we weren't to concerned about hitting the framing. We put a screw about every 4' or so. Along the bottom of the walls between the strapping, we stapled strips of ridge vent material (Cobra vent) to keep out critters and allow drainage.
I think the vinyl was Certainteed, since this is what our siding guy generally uses.
We discussed putting a second layer of tyvek over the foam (before the strapping went up), but opted not to as we couldn't figure out a way to attach it and figured the foil facing was a perfectly suitable WRB, and in the event of a failure, there was a layer of tyvek under that.
It's been over a year and the vinyl shows no signs of warping or sagging between the strapping. The entire process was fairly labor intensive, especially detailing around windows but we wouldn't hesitate to do it again.
WRB as backing to vinyl siding
Has anyone tried using a second layer of inexpensive WRB (tyvek?) over the furring strips to keep the vinyl siding from "waffling"? Pulling it tight is fast and achieves a flat surface. It went up fast and gives us a little insurance on high wind winter days. Any thoughts or concerns?
Cheers,
PK
Response to Paul Kuenn
Paul,
I have no idea if it will help, but it can't hurt.
Seems well worth it to put the extra 3/4” foam between furring strips. A tad more R value and a clear CYA to prevent the siding from failing a decade from now. It seems like you’d want a 1/2”? air gap between the furring strips and the filler foam to prevent holding water against the sides of the strips.
Nick,
That would work, but represents an awful lot more labour.
Furring Strip Dilemma -- I am rebuilding my 450 square foot, Northern Michigan cabin from the floor up. Walls are 2x4 with 1/2" OSB, then 2" XPS rigid foam, then 1/2" vertical strapping, then horizontal vinyl siding. I have finished most of the strapping but will not get to the siding until winter or spring -- probably spring since working with vinyl siding in winter may not be recommended ( and I do not care for working out in the cold when I don't have to ). But I may have made a mistake on my choice of furring strips! I used 1/2"x2-1/2" strips of OSB on 16" centers. I've recently been told that OSB furring will absorb moisture from the air and will swell and deteriorate under the siding. Is this true? Should I have used treated 1/2" plywood? I can still remove the OSB furring in the spring when I side the cabin. The furring is attached to the wall studs with 4" screws. Also, should I consider adding strips of furring between the 16" OC straps for added vinyl siding support?
Thanks! Tony
Tony,
Two issues: (1) Leaving OSB exposed (OSB can indeed swell and eventually deteriorate when exposed to rain), and (2) the thickness of your furring strips (most advice, including the advice of the Vinyl Siding Institute, is that the minimum thickness for furring strips under vinyl siding is 3/4 inch -- see image below). So your plan is not ideal.
“[Deleted]”
Tim,
1. According to the Vinyl Siding Institute, if you want to nail through exterior rigid foam to the underlying sheathing and studs, the maximum thickness of the rigid foam layer is 1 inch. Thicker rigid foam requires another layer of sheathing or (perhaps) furring strips. For more information, see "Fastening Vinyl over Foam."
2. Fastening vinyl siding to furring strips is controversial. For more information, see "Can Vinyl Siding be Applied Over Furring Strips?"
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