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Fastening Furring Strips to a Foam-Sheathed Wall

A screw manufacturer provides advice on how many screws you need

Posted on Nov 26 2010 by Martin Holladay

UPDATED March 1, 2012

If you’re building a house with foam sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , and your siding is installed over vertical rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. strapping installed on top of the foam, how should you attach the strapping? Most builders screw the strapping through the foam into the studs; so far, so good. But what length screws should you use? And how closely should you space the screws?

Answers to these questions can be found in a new technical bulletin published by FastenMaster, the company that manufactures Headlok screws. The bulletin, “Attaching Exterior Wall Covering Assemblies with Foam Sheathing to Wood Wall Framing,” is available from FastenMaster.

If you follow FastenMaster’s prescriptive recommendations, your furring strips will adequately support the weight of the siding and will secure the furring strips to the wall in a way that resists wind and seismic forces.

First, the basics:

  • You have to use 1x4s, since 1x3s could split. (If you want thicker lumber to allow for more secure siding attachment, you might consider using 2x4s.)
  • Fasteners used to secure furring strips must penetrate studs by at least 1½ inch.
  • FastenMaster provides prescriptive advice for walls with foam up to 4 inches thick; if your wall has thicker foam, you’ll probably have to consult an engineer.
  • FastenMaster’s recommendations work for Type II ESP, Type X XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation., Type 1 polyisoPolyisocyanurate foam is usually sold with aluminum foil facings. With an R-value of 6 to 6.5 per inch, it is the best insulator and most expensive of the three types of rigid foam. Foil-faced polyisocyanurate is almost impermeable to water vapor; a 1-in.-thick foil-faced board has a permeance of 0.05 perm. While polyisocyanurate was formerly manufactured using HCFCs as blowing agents, U.S. manufacturers have now switched to pentane. Pentane does not damage the earth’s ozone layer, although it may contribute to smog. , or for any foam with a density greater than one of these listed foams.

I have prepared two tables that incorporate FastenMaster’s recommendations. (My tables are more logical and easier to read than the table in the FastenMaster document, shown as Illustration 2, below.)

The first table below is for houses with studs spaced 16 in. on center; the second is for houses with studs spaced 24 in. on center.

Table 1: Fastener spacing for attaching furring strips if studs are 16 in. o.c.

Foam thickness Fastener spacing (assuming vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). siding) Fastener spacing (assuming fiber-cement siding) Fastener spacing (assuming stucco claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. ) Fastener spacing (assuming adhered manufactured stone veneer)
4 in. or less 24 in. 24 in. 16 in. 8 in.
3 in. or less 24 in. 24 in. 24 in. 12 in.
2 in. or less 24 in. 24 in. 24 in. 16 in.
1 in. or less 24 in. 24 in. 24 in. 24 in.

Table 1 notes:
Fasteners spaced 24 inches apart give you an allowable design wind pressure of 49 psf.
Fasteners spaced 16 inches apart give you an allowable design wind pressure of 73 psf.
Fasteners spaced 12 inches apart give you an allowable design wind pressure of 98 psf.
Fasteners spaced 8 inches apart give you an allowable design wind pressure of 147 psf.

Table 2: Fastener spacing for attaching furring strips if studs are 24 in. o.c.

Foam thickness Fastener spacing (assuming vinyl siding) Fastener spacing (assuming fiber-cement siding) Fastener spacing (assuming stucco cladding) Fastener spacing (assuming adhered manufactured stone veneer)
4 in. or less 24 in. 24 in. 12 in. Don’t do it
3 in. or less 24 in. 24 in. 16 in. 8 in.
2 in. or less 24 in. 24 in. 24 in. 12 in.
1 in. or less 24 in. 24 in. 24 in. 16 in.

Table 2 notes:
Fasteners spaced 24 inches apart give you an allowable design wind pressure of 33 psf.
Fasteners spaced 16 inches apart give you an allowable design wind pressure of 49 psf.
Fasteners spaced 12 inches apart give you an allowable design wind pressure of 65 psf.
Fasteners spaced 8 inches apart give you an allowable design wind pressure of 98 psf.

More information on siding weight

FastenMaster assumes that the weight of different types of siding (including the weight of the furring strips) are as follows:

  • Vinyl siding plus 1x4 furring: 2.3 pounds / square foot
  • Fiber-cement siding plus 1x4 furring: 3.5 pounds / square foot
  • Traditional stucco plus 1x4 furring: 12 pounds / square foot
  • Adhered manufactured stone veneer plus 1x4 furring: 26 pounds / square foot

Note: if you are attaching plywood or OSB rather than 1x4 furring, add 0.5 pound to the above weights.

If you know the actual weight of the siding you intend to install, you can substitute that weight for FastenMaster’s default values. Remember to add 1 pound / square foot for the weight of furring strips, or 1.5 pound / square foot for plywood or OSB sheathing. If your siding weighs less than FastenMaster's default values, you may be able to space your furring fasteners farther apart. On the other hand, if your siding weighs more than FastenMaster's default values, you may have to space your furring fasteners closer together. In either case, refer to the FastenMaster tables.

Design wind pressures

In the notes below each of the above tables, I have listed the design wind pressures (in pounds per square foot) that these wall assemblies are designed to resist. More information on design wind pressures can be found in Table R302.2(2) of the International Residential Code.

Most homes in the U.S. are designed to resist wind speeds up to 90 mph. However, in coastal areas, the design wind speed is much higher; it is 130 mph in some coastal areas and 150 mph in south Florida.

If your design wind speed is 90 mph, and your home is located in a typical suburban or wooded location, your design wind load is 19.5 psf. If your design wind speed is 90 mph, and your home is located in open, flat terrain, your design wind load is 29.1 psf. For these locations, all of the FastenMaster recommendations are more than adequate. If you live in an area with a design wind speed above 90 mph, however, you should verify that the your furring attachment method is adequate for your local design wind pressure.

Siding attachment requirements

Okay, now your furring strips are firmly secured to your building. The next question is: how do you attach your siding to the furring strips? After all, once you have installed vertical 1x4 strapping over foam sheathing, your siding nails are embedded in only ¾ in. of wood. Is that enough?

Table R703.4 in the 2006 IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. (“Weather-Resistant Siding Attachment and Minimum Thickness”) specifies the required minimum fastener lengths for attaching siding. Moreover, in Footnotes n, p, and y — footnotes that apply to some, but not all, types of siding — the IRC notes that fasteners must “penetrate framing 1 1/2 inches.”

Confusingly, however, Table R703.4 provides no guidance to builders installing siding on furring strips over foam sheathing. The table anticipates several scenarios, including “fiberboard sheathing into stud,” “gypsum sheathing into stud,” “foam plastic [presumably without furring strips] into stud,” and “direct to studs.” Each of these scenarios deserves its own column in the table. However, there is no column for “furring strips over foam sheathing.”

Until recently, many siding manufacturers recommended that siding nails penetrate 1 in. or 1¼ in. into wood. That’s beginning to change, however. The Vinyl Siding Institute requires only ¾ in. of fastener penetration for vinyl siding; James Hardie Corp. accepts only 7/16 in. of penetration for fiber-cement lap siding.

According to building scientist Joseph Lstiburek, if you have any doubts arising from the fact that your siding nails penetrate into only ¾ in. of wood, just switch from smooth-shank nails to ring-shank nails. Unless you’re building near the coast in south Florida, ring-shank nails will be more than adequate, even when penetration into wood is only ¾ in.

If you have more questions about attaching furring strips to foam sheathing, or to request a copy of “Attaching Exterior Wall Covering Assemblies with Foam Sheathing to Wood Wall Framing,” call the FastenMaster Technical Support team at 800-518-3569.

More information

For more information on this topic, see these useful articles:

Last week’s blog: “Makeup Air for Range Hoods.”

Tags: , , , , , ,

Image Credits:

  1. Image #1: Rob Wotzak
  2. Image #2: FastenMaster
  3. Image #3: Cold Climate Housing Research Center
  4. Image #4: JLC
  5. Image #5: Dow Building Solutions

Nov 26, 2010 1:27 PM ET

Thanks for the Article
by Michael Schonlau


This is why I like this site. I've had trouble finding any details on fastening siding to furring strips on a wall with exterior rigid foam insulation. Your article is vey timely for me. I appreciate you providing more info on this overlooked detail. Thanks again.

Nov 26, 2010 5:24 PM ET

Technical Bulletin
by Josh Ayoroa

I am having trouble finding the bulletin you refer to in this post. "Attaching Exterior Wall Covering Assemblies with Foam Sheathing to Wood Wall Framing" could you provide a link or instructions on how to access it please.


Nov 27, 2010 6:00 AM ET

Response to Josh Ayoroa
by Martin Holladay

The document is not posted online. As I noted in the last paragraph of the article, "to request a copy of 'Attaching Exterior Wall Covering Assemblies with Foam Sheathing to Wood Wall Framing,' call the FastenMaster Technical Support team at 800-518-3569."

The illustration for the article on this Web page depicts the original FastenMaster table.

Nov 27, 2010 9:47 AM ET

Angle the screws
by Garth Sproule

I believe that it was Thorsten Chlupp who advised angling the screws at an upward angle of five degrees to help prevent future sagging of the cladding. Have you seen any research regarding this ?

Nov 27, 2010 10:10 AM ET

Response to Garth
by Martin Holladay

I don't know of any research that looks at that specific method.

However, the FastenMaster recommendations are based on engineering calculations, and should satisfy most hard-to-satisfy engineers.

Joe Lstiburek and his colleagues at the Building Science Corp. have also done a variety of tests with mockups, to see how much weight can be hung from furring strips attached with a variety of fasteners. Joe's conclusions: the FastenMaster recommendations are very conservative, and are likely the provide stronger than necessary results.

Nov 27, 2010 10:44 AM ET

Thorsten Chlupp Detail
by John Brooks

The other nice thing about Thorsten's detail...
water would be more likely to "drain away"

Nov 27, 2010 12:10 PM ET

by Dan Kolbert

But the heads would stick out more.

Nov 27, 2010 3:02 PM ET

Related Document
by John Brooks

Here is a link to the Document that Thorsten worked on

Nov 27, 2010 4:55 PM ET

angling screws has an obvious benefit
by Anonymous

try to do an iron cross on the rings and get back to me. The angled screw has a vector component that opposes downward force of gravity. A horizontal screw only has friction to oppose such.

Nov 27, 2010 4:58 PM ET

engineers or philosphors
by Anonymous

This site could use more engineers and less couch potatos and amateur Gandhi wanna be's

Nov 27, 2010 7:29 PM ET

by Kevin Dickson, MSME

I'm getting ready to finalize construction drawings using this type of wall, so thanks. I'm still a bit fuzzy on how to install "outie" windows. Could you direct me to a good cross-section of that detail?

Nov 27, 2010 9:57 PM ET

by Raff

Kevin, both the innie and outie window install detail is in the REMOTE manual

I installed most of my windows in outie fasion, all basement windows using innie fashion. I strapped 5.5" of foil faced polyiso with horizontal 1x4 pine (16"OC) secured with 8" Deckfast panel screws at a slight upward angle. My PEng was more than satisfied with this detail.
The above manual is VERY informative and the guys at CCHRC are great to get additional info from ;)

Nov 27, 2010 11:18 PM ET

by bpi na

Just an FYI.... I have 30 year old deck screws on past jobs failing, rusting out.

Now am stainless steel screw guy.

Nov 27, 2010 11:25 PM ET

Response to Michael Schonlau
by jeff_williams

I also had trouble locating information on this method online but decided to email the manufacturer directly (James Hardie in my case) and in only a few hours I had all the details I needed for the install and the product warranty was still preserved. I recommend the same for any product you're considering.

Nov 29, 2010 10:39 PM ET

Depth of Fastener
by Bruce Miller

Can anyone tell me if the penetration of a Headlok screw through CDX plywood sheathing (say 1/2") fastened to the framing would count for any of the 1 1/2" required fastener depth into a 2x4?

Nov 30, 2010 2:11 AM ET

Poential contradictions in IRC to your assertions on nailing
by Bob Ellenberg

As always I appreciate your research and input but have a couple of questions regarding this.

First of all, I have looked but have not been able to find Hardi specs for 7/16" penetration and I have most of their technical bullentins. Could you share which one has that specified?

But more important is Table R703.4 as it is the code which we must adhere to. In referenceing it, you state, "However, the table doesn’t specify any minimum fastener penetration into wood.", I believe it does give it at 1.5" into framing. There is a column labeled Foam plastic sheathing into stud which is exactly what you are discussing. For this column, it gives notes "n", "p" and "y" which apply to different siding materials but all state the fastener must accomodate the sheathing and penetrate the framing 1.5". This is also stated in the Building Science Corp. article you referenced and they further stated if you do it differently you will need engineering to meet the code.

I agree with their statement unless I have missed something and do not believe you can use these fasteners with 1x nominal material unless you have an engineer state it will have the equivalent holding power as what the prescriptive code requires.

Here is an alternate idea which is more costly if you had only planned to add 1" of foam but meets the code and adds more insulation. Unless using brick, as you and BSC have discussed in the past, the space behind the siding doesn't need to be 3/4", it can be quite small. Cover your studs in 1"-2" of foam to give you the thermal break. Then rip studs with a thin kerf blade giving you two pieces 1-5/8" to 1-11/16" thick. Fasten those as you describe above for the 1x material. Then fit 1-1/2" thick foam sheets snuggly between them and calk any gaps. I belive you could do the WRB on the base layer of foam or just below the siding but the drainage plane would probably perform better if it were a the base layer of foam. Fasten your siding into the furring strips which meet the code thickness and give you a 1/8" drainage plane.

Nov 30, 2010 6:34 AM ET

Response to Bruce Miller
by Martin Holladay

Q. "Can anyone tell me if the penetration of a Headlok screw through CDX plywood sheathing (say 1/2") fastened to the framing would count for any of the 1 1/2" required fastener depth into a 2x4?"

A. As far as I understand the FastenMaster recommendations, the answer is No. For further information, however, you may wish to contact Brice Hereford at FastenMaster. His e-mail address is
BHereford [at] olyfast [dot] com

Here's one problem: every 4 feet, the screw lands on a gap between two sheets of plywood, and there aren't many wood fibers in the gap to help hold the screw.

Nov 30, 2010 6:49 AM ET

Response to Bob Ellenberg
by Martin Holladay

The statement that 7/16 in. of nail penetration satisfies the James Hardie Co. came from a Hardie technical rep, who assured me over the phone that 7/16 in. was enough. That statement is implied, but not made explicit, in the following sentence from the installation instructions for HardiePlank lap siding:"HardiePlank lap siding can be installed over braced wood or steel studs spaced a maximum of 24" o.c. or directly to minimum 7/16" thick OSB sheathing."

Here's the link to the document:

Thanks for drawing my attention to footnotes n, p, and y to Table R703.4. I will correct my blog to reflect those footnotes.

Joe Lstiburek states that ring-shank nails will solve this problem, but evidently builders may need an engineer to certify that fact.

Nov 30, 2010 11:35 AM ET

Bruce's question regarding penetration
by Brice Hereford

Q. "Can anyone tell me if the penetration of a Headlok screw through CDX plywood sheathing (say 1/2") fastened to the framing would count for any of the 1 1/2" required fastener depth into a 2x4?"

There are two inches of thread on the HeadLok and the values given are based upon 1 1/2 inches of penetration. The values are based on only 1 1/2 inches of penetration in the stud! So if you get the 1 1/2 inches into the stud, leaving a half inch in the CDX, you will be okay! I recommend that you put the full two inches of thread into the stud. More is better!

Nov 30, 2010 11:47 AM ET

Additional info on James Hardi requirements and IRC
by Bob Ellenberg

I remembered seeing additional information somewhere so I did a little digging this morning.

This page on Hardi's website, , has all of their documents and requirements and has the Legacy report, NER-405 which covers all of the different code requirements. If you go specifically to the Best Practices for lap siding document--not panel siding, it discusses installation over furring strips as well as nailing into OSB. In describing how and where you can use 1x furring strips and meet codes, it refers to some of the tables in the NER-405 (a 35 page report). What the Best Practices document does not tell you (requires digging through the NER-405) is that it is ONLY the tables covering the UBC, SBC and BOCA that approve it--not the IRC. The report goes into different wind loads and shear loads which is emphasized in the IRC and specificallyl requires 1-1/2" penetration specifically into framing.

Realistically your research of these type of questions and details is not only more in depth than contractors and designers typically have the time to do, it is often more in depth than many code officials have been able to do. The IRC gives the code official the authority to approve alternative methods. If you are under the IRC and not in a high wind or seismic zone, you can certainly approach your code officials armed with these documents and ask for approval using 1x material.

Nov 30, 2010 12:21 PM ET

James Hardie recommendations
by Martin Holladay

I've clicked on the links to the Best Practices documents, and I've skimmed the NER-405 document, and I can't find any references at all to installations using furring strips over foam.

Can you be more specific about where this information can be found? For example, can you provide a link to the document -- not a link to the overview page -- and a reference to a page number?

Nov 30, 2010 3:29 PM ET

Hardi Recommendations
by Bob Ellenberg

Sorry, I left out one step and a section of the 405 referenceing the IRC (I said I had to dig to get this) and it is as clear and mud--very thick mud! I'll go a little deeper into what I found and how I read it.

Go to the link, scroll down and click on the icon above the words HardiePlank pg. 78-89, and from that one scroll down to the bottom of page 81 which will state that face nailing may be required for some installations and code requirements, and then refers you to Appendix B. Go back to the link and click on the icon above the words Appendix/Glossary pg. 108-128. Starting on page 108 they discuss how to install over furring strips and specifically state that it must be installed with the same penetration and and holding power specified in the NER-405. They go on to state "When attaching lap siding products over wood furring, the typical fastener used is the 1-1/4” long No. 11 ga. roofing nail, blind nailed. This fastener is going to be the shortest fastener
approved for fastening lap siding products, therefore the furring must be a minimum of 0.75” thick to achieve the same values as NER-405 Table 2 states for the 11 ga. 1-1/4” roofing nail given
plank reveal, stud spacing, building height and exposure category." I'll get back to this statement later.

Go again back to the link and click on the link to the NER-405. This report in turn gives specifics for every Hardi product and every code. For example, take one that references nailing to OSB. On page 131 (which is actually page 3 of the Legacy Report), left side, 3.2.6 for Hardishingle, it states over plywood you refer to tables 6A, 6B and 6C and for over OSB you refer to tables 7A 7B and 7C. The tables start on pages 142 (page 14 of 35) and you will see that all of these tables list several codes but not the IRC. If you back up to page 140, they reference equivalent wind speeds for the IRC and how to convert it to the BOCA. Where it gets tricky is determining penetration requirements and reading between the report and the actual code. My understanding is a Legacy report CAN be accepted by the AHJ but is not automatic or mandatory, particularly if it is a lesser requirement. The manufacturer's recommendation (the above referenced Appendix B where they state if you use furring strips, says it must have the same penetration as called for in the 405 report. When you look at the tables, they do not specifically state that the fasteners have to go into the framing. But if you refer back to section 7.3.1 on page 140 (12 of 35), it states specifically that the referenced tables 2a and 2b provide capacity ratings for Hardi siding attached to studs. I believe the implication there is pretty clear that the fasteners have to go into the framing (except when you are attaching to sheathing using those specifications). Also if you scan through the list of documents Hardi submitted to get this report (laboratory and P.E. testing) you will see that many of them refer specifically to the test being conducted with the fastners penetrating the framing. However, for some of their products, they were clearly tested for fastening to sheathing, but not all of the products.

I may not be right on the reading of the report as you need to be both an attorney and an engineer to decipher it, but I think I am. Since it treats fastening some of the products to OSB but not all of them and gives different specifications for that fastening, I don't believe we can take that shallow penetration and apply it to furring strips (as far as code compliance is concerned) and in their Appendix, Hardi stated it had to have the same penetration as the 405 report calls for. Clearly the 703.4 table in the IRC states 1.5" but does the referenced 405 only require 3/4", as stated in the Hardi Appendix?

Per the tables in the 405, the use of 1-1/4" roofng nails is ONLY when going through a single 5/16" thickness of Hardi product. When it is lapped and nailed through the overlap, the 405 calls for 2". So a 1-1/4" nail going through a single thickness of siding penetrates the framing 15/16" of an inch--3/16" more than you get with a nonimal 1x.

And just to muddy it up a little further, if you consider that in the Appendix Hardi gives pretty specific direction on fastening it over 1x furring with a 1-1/4" roofing nail and that appears to conflict with the 405, section 4.0 Installation, on page 135 (page 7 of 35) states that if there is non-editorial differences between the manufacturer's product information sheet and the 405 report, the report is null and void! So where does that leave your code compliance?
I've spent way too much time this morning but I continue to learn how complex some of these details are and it helps me realize how much I don't know and how much attention I must pay to every detail of building.

Nov 30, 2010 3:46 PM ET

Thanks, Bob!
by Martin Holladay

Thanks very much for digging into this so thoroughly and sharing what you found. I appreciate it.

Okay, all you code people out there, here's your homework: we need more clarity in the building code on this issue. During the next code cycle, please introduce code changes to provide clear guidance on how builders can attach furring strips through foam sheathing, and how siding can be fastened to furring strips.

For readers interested in cutting to the chase: the most interesting and potentially useful guidance from James Hardie can be found in this document:

Here are the most relevant passages:
"Attaching lap siding to wood furring: When attaching lap siding products over wood furring, the typical fastener used is the 1-1/4” long No. 11 ga. roofing nail, blind nailed. This fastener is going to be the shortest fastener approved for fastening lap siding products, therefore the furring must be a minimum of 0.75” thick to achieve the same values as NER-405 Table 2 states for the 11 ga. 1-1/4” roofing nail given plank reveal, stud spacing, building height and exposure category."

The document also states:
"Attaching panel siding to wood furring: When attaching panel siding products over wood furring, the typical fastener used is the 6d common 2” long nail. This fastener is going to be the shortest fastener approved for fastening panel siding products into wood, therefore the furring must be a minimum of 1-11/16” thick to achieve the same values as NER-405 Table 2, given stud spacing, building height, and exposure category. It is deemed an acceptable practice to not fasten along the top and bottom plates for the 5/16” HardiePanel configurations listed in the NER-405 using the following fastener type:
• 0.091” shank X 0.225” HD X 1.5” long ring shank nail
• 6d common 2” long nail
• Min. No. 8 X 0.311 HD X 1” ribbed bugle head screw
• 0.10 X 0.25” HD X 1.5” long ET&F pin or equivalent
Conditions of use:
• This practice is acceptable for transverse load only.
• This practice is not acceptable for racking shear values or in-plane
forces other than perpendicular/normal wind forces.
• All vertical joints shall occur over framing.
• All other James Hardie Installation Requirements shall be followed."

Dec 1, 2010 10:01 AM ET

Always vertical?
by Pat Murphy

Does this article imply the furring/strapping is always vertical? What is the effect on the rain screen?

Dec 1, 2010 10:24 AM ET

Response to Pat Murphy
by Martin Holladay

If the engineering calculations (or the FastenMaster table) indicate that you can space your screws every 24 inches, then there is no reason you can't use horizontal strapping. If your studs are 24 in. on center, then the horizontal strapping gets one screw per stud.

However, if the engineering calculations or the table indicate that you need to install your furring strip screws every 8 in. or 12 in., you'll have to consult an engineer, because studs aren't spaced that closely.

There is a secondary concern: horizontal furring strips (generally used for cedar shingle siding) don't allow drainage of liquid water unless the furring strips are regularly kerfed on the back. These kerfs introduce new questions -- do they weaken the furring strips and therefore change the ability of the furring strips to resist wind pressures?

I used horizontal furring strips over EPS foam on my own house, built in 1980. The furring strips aren't kerfed. I don't think the lack of drainage for liquid water makes any difference. Very little liquid water gets past my siding, and the air gap between the foam and the shingles dries readily, due to air movement -- the pumping action driven by temperature changes -- and diffusion through the shingles.

Dec 2, 2010 4:35 PM ET

Exterior foam systems....
by Ed Latson

Hey, there folks...let's take off the Neanderthalian approaches......Og and Grog can be left back in the cave.........................
Check out and their R-ETRO SYSTEM.......rain screen/short screws/panels/attachment for horizontal/vertical siding..or acrylic stucco...R-10 or 18 or 26 systems-use them outside/inside/against your cellar wall ....even on the ceiling....GREAT tech support via the wholesalers and the company........THIS IS THE BEAUTY OF OUR 20 YEAR WAIT FOR REALLY COOL STUFF THAT WORKS IN MODERN BUILDING can spend 3 weeks on their website and another 4 weeks studying their pdf manuals-ALL EXPERTLY WRITTEN AND ILLUSTRATED......AND CALL OR EMAIL IF YOU HAVE QUESTIONS.......QUADLOCK-period.

Dec 2, 2010 5:00 PM ET

Exterior foam systems....Part 2
by Ed Latson

My apologies, but I failed to mention this:
This is what Amory Lovins/Rocky Mtn Institute/CO is trying to get us to----efficient/damn good sysytems that work right the first time/ hopefully with decreasing costs (because of our efficiencies..) and making retrofitting our older building stock 'fair' for all.......remember-$$$$$'s are a green resource,too......'.Latson'

Dec 2, 2010 5:44 PM ET

Easy to miss studs?
by Dan Burgoyne

In the case of foam over exterior plywood shear sheathing over framing, it seems like screwing through 1x furring strips and several inches of rigid foam would make it pretty difficult to hit studs that you can't even see on the other side of sheathing. Do you have any suggestions to increase odds of hitting framing? If some of them miss, and just go through 3/8" CDX sheathing, does this weaken the structural integrity of furring supporting exterior finish?

Dec 2, 2010 8:14 PM ET

Response to Dan Burgoyne
by Martin Holladay

Use accurate layout and marking methods. When in doubt, walk into the house and look for the screws from the inside.

Dec 2, 2010 8:59 PM ET

wood siding
by mike keesee

your tables cover everything but wood siding. What's the guidance on wood siding?

Dec 2, 2010 10:55 PM ET

board and batten over foam
by mjb

I'm envisioning a scenario where 1.5" foam outsulation would be interrupted every two feet horizontally by a 2 x 2, then housewrap over that, then corovent rainscreen installed over the 2 x 2's position, and finally board and batten siding nailed with nails long enough to shoot through the vent and into the 2 x 2 to achieve the required penetration into solid wood. There's obviously a thermal bridge there, but could it be deemed as an acceptable trade-off in order to attach the siding properly?

Dec 3, 2010 5:39 AM ET

Response to Mike Keesee
by Martin Holladay

Mike Keesee,
Wood lap siding weighs less per square foot than fiber-cement, so you should be fine with screws spaced 24 in. apart.

Dec 3, 2010 5:43 AM ET

Response to MJB
by Martin Holladay

Your proposed wall will work fine, as long as your rigid foam meets the minimum R-value requirements for your climate zone and stud depth. To determine the minimum R-value of your foam, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

Dec 4, 2010 12:00 PM ET

FastenMaster Technical Bulletin
by Rob

This morning (12/04/2010 10:45am) put the HeadLok Technical Bulletin on our website. It can be found here:

Dec 4, 2010 12:03 PM ET

Please no wood furring strips
by Michael Strong

Ouch! Please remove the wood furring strip in the photo. Down here where its hot and humid anything but wood for a furring strip please. They will rot out before you get your first coat of paint on the siding. We like to use Azek composite materials. Nice blog Martin!

Dec 4, 2010 5:18 PM ET

Response to Michael Strong
by Martin Holladay

How in heaven's name are you building your rainscreens? Are they ventilated? Or are you somehow wrapping your furring strips in polyethylene (heaven forbid)?

There is absolutely no reason why vertical wood furring strips installed in a ventilated rainscreen should "rot out before you get your first coat of paint on the siding." You must be doing something seriously wrong.

Dec 4, 2010 8:20 PM ET

OSB Furring
by Tom Barthelemy

In reference to not using 1x3 because they might split, I have been using 3/4 OSB as furring for a couple decades now, mostly in interior applications. Some time on the table saw ripping them out, but they never split and cost less as well. Also, contrary to what I hear and maintained myself for a while, OSB takes a whole lot of water and exposure to rot. It does swell if it gets wet, but I'd use it under a fairly tight sidng such as cedar or Fiber Cement. If you are using a loose siding such as vinyl or steel lapsiding, OSB might not be the best choice.

Personally, I resist using vinyl siding because when installing the stuff I have to wear a bag over my head, which makes it real hard to see.

Dec 4, 2010 8:23 PM ET

On rotting windscreens
by Tom Barthelemy

Martin - pine 1x material rots pretty easily, especially when regularly wetted in a hot climate.

Dec 5, 2010 6:47 AM ET

Response to Tom Barthelemy
by Martin Holladay

Pine 1-by exterior trim rots incredibly quickly, I agree, but that's because it is exposed to the rain.

Rainscreen strapping may see slight wetting in extreme rain events, but those events are very rare, and the amount of liquid water reaching the strapping will be very little. Due to the fact that the rainscreen is ventilated, the strapping will dry very quickly. Since the sun should hit the siding occasionally, the air space behind the siding will be hot and dry.

If your rainscreen strapping is rotting very quickly, you have made serious flashing errors.

Dec 7, 2010 12:07 PM ET

Semi-rigid mineral wool sheathing
by Mark Kerschbaumer

We recently completed a home in North Vancouver BC and used 2" of semi rigid mineral wool (Rock Board 60 from Roxul). This is my preferred material mainly because of its high vapour permeability and ability to shed/repel water. Biggest challenge was to agree on best way to attach strapping as it is not as rigid as other foam stock and ended up using 1x4 fir screwed into 24 o/c studs and selecting cedar bevel over hardie siding because of weight and 'wavie-ness' potential. So far so good. This was sort of new ground for the Roxul folks so I am interested in what comments the forum might have on this.

Dec 7, 2010 12:11 PM ET

Response to Mark Kerschbaumer
by Martin Holladay

How did you prevent the furring strips from compressing the Roxul? Did you put standoffs (for example, short lengths of PVC pipe) between the furring strips and the sheathing?

Dec 8, 2010 9:44 PM ET

Martin I recall the width of
by Mark Kerschbaumer


I recall the width of the 1x4 was sufficient to disperse the compression forces and there was an aluminum angle at the bottom to support the Roxul vertically. I will check with the builder to confirm this. I

Dec 10, 2010 1:15 PM ET

Martin. Just heard back from
by Mark Kerschbaumer


Just heard back from the builder. They ended up nailing off the 1x4 6-8" o/c, then screwing it off. The nails provided even pressure whereas the screws were trickier to keep consistent. Would be nice if Roxul made a stiffer board for this sort of application.

Jan 1, 2011 12:17 PM ET

Furring strip material
by Rob Dickinson

I really appreciate how useful this forum is, as there is always good discussion on topics just when I need the information!

I am trying to decide just what material to use for the furring strips on my exterior insulation project. We're attaching 4" of foil-faced polyiso boards to a stick-framed house with 2x4 walls 24" OC.

We were originally going to use cedar 1x4 material, given that cedar is fairly moisture-tolerant, but the cost of the furring strips is more than I was expecting. So now we're looking at other materials to see if we can save on costs.

The house is in the Eugene Oregon area, where rain is a way of life. ;-) So while I appreciated Martin's comments on how pine furring would dry out normally when used in a rainscreen assembly, I didn't know whether I should still avoid it given our wet climated. Martin -- would you still think pine is OK in a rainy environment?

If I discount my own labor and spend some money on primer, I might still save money using primed pine over the cost of cedar 1x4s.

Another option might be to use pressure-treated 1x4s, which turn out to be cheaper than cedar stock. Given we want to avoid any chemical interaction with the underlying foam, we would probably lay down strips of our tyvek WRB over the foam and under the pressure treated furring strips (if we use PT furring material at all).

Finally, the Thorsten Chlupp article (and the FastenMaster info) talk about using 3/4" plywood strips for furring material. This would be cheaper still, and would cut the cost of the furring strips in half. Should I be concerned about the weatherability of exterior CDX in our rainy climate when used in a rainscreen? (Again, I could go wild with primer if that would help and the cost would still be lower)

Finally, I am wondering if I can use the same spacing for the TimberLok/HeadLok screws if I use 3/4" CDX plywood. The chart from TimberLok (in their technical document) seems to indicate a minimum 12" spacing when using 3/8" minimum WSP (wood structual panel), which is twice as much as for 1x4 furring strips. I don't know if that would still be true for 3/4" material which is a lot more robust. But if I read their table conservatively, I would guess I would need to use twice as many screws, which would negate any savings from using the cheaper plywood furring strips. (I'll probably contact TimberLok, but I bet someone on this list has already tracked down this info)

Thanks for any advice on this material selection.

Jan 13, 2011 11:17 PM ET

Changes in the 2009 IRC
by Bob Ellenberg

Martin--I am doing a pretty thorough review of the 2009 IRC to find the subtle changes from the 2006 and low and behold, I found a change that impacts the long discussions we had at the beginning of these comments. Remember the notes in table R703.4 that required the siding fasteners to penetrate the framing 1.5"? Well section R703.10.1 in the 2009 for fiber cement panel siding allows you to use the manufacturers method, "Panel siding shall be installed with fasteners according to Table R703.4 or approved manufacturer's installation instructions." Hardi's instructions that you referenced could be used under the 2009. It goes on to give the same OK for lap siding.

Jan 14, 2011 6:11 AM ET

Response to Bob Ellenberg
by Martin Holladay

Thanks very much for the useful information.

Feb 10, 2011 1:21 PM ET

what about wood siding over SIPs?
by Jay Hersh

I'm thinking of using a liquid water barrier like StoGuard or Tyvex liquid applied membrane with HomeSlicker between it and wavy edge bezel hung wood siding we're thinking of using. This would be over the top of SIPs.

Would there be anything different in doing this from your guidelines above?

Feb 10, 2011 2:40 PM ET

Response to Jay Hersh
by Martin Holladay

I don't understand your question. This blog is about fastening furring strips to studs through foam sheathing.

The wall assembly you are suggesting will have
(a) no studs,
(b) no exterior foam sheathing, and
(c) no furring strips.

So how does a discussion about fastening furring strips to studs through foam sheathing apply?

Feb 11, 2011 10:25 AM ET

let me rephrase
by Jay Hersh

My concern was with how to properly secure the bezel boards to the SIPs and whether I would need furring strips to do this (sounds like the answer is no) or can attach the siding directly to the SIP and if so what the fastener spacing should be. Maybe this still isn't the right place to ask this question.

Feb 11, 2011 10:56 AM ET

Fastening siding to SIPs
by Martin Holladay

When siding is installed on SIPs, the siding is usually attached to the OSB facing. If you have any further questions about fastening siding on SIPs, just contact your SIP supplier.

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