Image Credit: Image #1: Rob Wotzak
More Musings of an Energy Nerd
UPDATED March 1, 2012
If you’re building a house with foam sheathing, and your siding is installed over vertical rainscreen 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 XPS, Type 1 polyiso, 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.
Weekly Newsletter
Get building science and energy efficiency advice, plus special offers, in your inbox.
This article is only available to GBA Prime Members
Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.
Start Free TrialAlready a member? Log in
78 Comments
Thanks for the Article
Martin,
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.
Technical Bulletin
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.
Thanks.
Response to Josh Ayoroa
Josh,
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.
Angle the screws
Martin
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 ?
Response to Garth
Garth,
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.
Thorsten Chlupp Detail
The other nice thing about Thorsten's detail...
water would be more likely to "drain away"
angle
But the heads would stick out more.
Related Document
Here is a link to the Document that Thorsten worked on
http://www.cchrc.org/docs/best_practices/REMOTE_Manual.pdf
angling screws has an obvious benefit
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.
engineers or philosphors
This site could use more engineers and less couch potatos and amateur Gandhi wanna be's
Windows
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?
windows
Kevin, both the innie and outie window install detail is in the REMOTE manual
http://www.cchrc.org/docs/best_practices/REMOTE_Manual.pdf
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 ;)
screwed
Just an FYI.... I have 30 year old deck screws on past jobs failing, rusting out.
Now am stainless steel screw guy.
Response to Michael Schonlau
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.
Depth of Fastener
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?
Poential contradictions in IRC to your assertions on nailing
Martin,
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.
Response to Bruce Miller
Bruce,
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.
Response to Bob Ellenberg
Bob,
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:
http://www.jameshardie.com/pdf/install/hardieplank-hz5.pdf
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.
Bruce's question regarding penetration
Bruce,
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!
Additional info on James Hardi requirements and IRC
Martin,
I remembered seeing additional information somewhere so I did a little digging this morning.
This page on Hardi's website, http://www.jameshardie.com/builder/bestPractices.shtml , 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.
James Hardie recommendations
Bob,
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?
Hardi Recommendations
Martin,
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.
Thanks, Bob!
Bob,
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:
http://www.jameshardie.com/pdf/best-practices/hz/hz5-108-128.pdf
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."
Always vertical?
Does this article imply the furring/strapping is always vertical? What is the effect on the rain screen?
Response to Pat Murphy
Pat,
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.
Exterior foam systems....
Hey, there folks...let's take off the Neanderthalian approaches......Og and Grog can be left back in the cave.........................
Check out http://www.quadlock.com 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 SCIENCE......you 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.
Exterior foam systems....Part 2
My apologies, but I failed to mention this:
HANDS ON, FULL DAY TRAINING SEMINARS AT THE WHOLESALER'S OFFICE AND WAREHOUSE.....PLUS ON-SITE HELP FOR YOUR FIRST JOB OR TWO BY THE WHOLESALER......IT FEELS LIKE A EUROPEAN COMPANY-THEY WANT YOU TO GET IT RIGHT-TO MAKE A FAIR PROFIT- AND TO PROVIDE YOUR CLIENT WITHA TOP-NOTCH JOB.....
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'
Easy to miss studs?
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?
Response to Dan Burgoyne
Dan,
Use accurate layout and marking methods. When in doubt, walk into the house and look for the screws from the inside.
wood siding
your tables cover everything but wood siding. What's the guidance on wood siding?
board and batten over foam
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?
Response to Mike Keesee
Mike Keesee,
Wood lap siding weighs less per square foot than fiber-cement, so you should be fine with screws spaced 24 in. apart.
Response to MJB
MJB,
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.
FastenMaster Technical Bulletin
This morning (12/04/2010 10:45am) put the HeadLok Technical Bulletin on our website. It can be found here: http://www.fastenmaster.com/Files/TechnicalCodeFiles/48/DocumentFile/101104%20FastenMaster-Headlok%20Technical%20Bulletin%20(wood%20final).pdf
I think this is the current one the shows the info on the Headlok https://d3g5z6m6vcoqo2.cloudfront.net/resources/ter_1009-01_2022-10-03-125505_ivoe.pdf
Please no wood furring strips
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!
Response to Michael Strong
Michael,
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.
OSB Furring
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.
On rotting windscreens
Martin - pine 1x material rots pretty easily, especially when regularly wetted in a hot climate.
Response to Tom Barthelemy
Tom.
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.
Semi-rigid mineral wool sheathing
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.
Response to Mark Kerschbaumer
Mark,
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?
Martin
I recall the width of
Martin
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
Martin.
Just heard back from
Martin.
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.
Furring strip material
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.
Changes in the 2009 IRC
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.
Response to Bob Ellenberg
Bob,
Thanks very much for the useful information.
what about wood siding over SIPs?
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?
Response to Jay Hersh
Jay,
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?
let me rephrase
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.
Fastening siding to SIPs
Jay,
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.
splitting 1x3s
I just reread this column and said yikes, because I've got a pile of 1x3 cedar headed to my place in an hour or two.
Splits when exactly? Assuming I predrill every hole for the 3/8" fasteners I'll be sending through, will it probably be okay? Or, will it split when I nail the siding to it?
Response to Minneapolis
Minneapolis,
I hope you got a good price on the cedar. Here in Vermont, cedar is expensive. I wouldn't spring for cedar for a dry, protected location (furring strips) -- I would use spruce or fir.
Anyway, you'll be fine. Here's what determines whether your furring strips split: the diameter of the the fastener, the number of knots in the lumber, and the intelligence and care of the installer.
With a clumsy installer, a fat screw, and knotty wood, you'll get a lot of splitting. With a smart installer, a slender screw, and few knots, nothing will split.
Any if you pre-drill everything, of course the wood won't split. You'll just spend a long time drilling holes.
Glad to hear it. I was going
Glad to hear it. I was going to have someone pre-drilling anyway, in the hope that it will make aiming the screws a little easier.
For what it's worth: I got a so-so price on the cedar (approx 0.26/lf), but checking back with them now, it sounds like their only cheaper option would have been pine--fir was approx twice as expensive as their cedar.
I did, however, get a pretty nice price on the stacks of polyiso, and the 10" SPAX screws (yes, I'm trying to go thick on the foam) are on sale this week, lucky us. Thanks.
Nails Instead of Screws
Sorry if this has already been discussed.
Why screws as opposed to ring-shank nails? Cheaper, easier, faster.
Is there a concern about pull-out from the foam flexing over time? I would rather shoot two nails than drive one screw...
Response Thomas Farwell
Thomas,
Unless you are installing very thin foam, the length of the required fastener exceeds the maximum length of available nails for nail guns. They don't make 'em that long. So you need screws.
Where is the FastenMaster bulletin?
I haven't been able to find the FastenMaster bulletin anywhere, although Certainteed's website also refers to it. The link posted by Rob doesn't work for me. Is the document currently available anywhere?
The Foam Sheathing Coalition (whatever that is) has this document, which has spacing requirements for various types of fasteners for foam up to 4 inches thick (including nails, in case you prefer to use 7-inch nails):
http://www.foamsheathing.org/images/TM_Cladding_Attachments_Through_Thick_Foam_Sheathing.pdf
Does this appear reliable?
Response to Ian Brown
Ian,
It certainly seems as if FastenMaster has removed the technical bulletin from their website. If you need a copy, I suggest you send your request by e-mail to Brice Hereford, FastenMaster's code compliance specialist:
BHereford [at] olyfast [dot] com
furring strip material
Can Azek or other non-wood material be used as furring strips in a wall with 2" of rigid foam "outsulation" and fiber-cement cladding? Whatever I use must be able to support the weight of the cladding. For fiber-cement board, I think I need 3/4" thick material at a minimum.
Response to Stuart Murray
Stuart,
Furring strips need to hold fasteners. I'm not familiar enough with Azek to know how well the material holds nails and screws, but I can't imagine a single advantage of Azek over spruce or fir in this application. Azek is designed to look pretty and be exposed to the weather, and it is expensive. Spruce or fir are both excellent at holding screws and nails, and the price is right.
Pancake heads
Is the head thickness of these screws negligible enough to not worry about it affecting the straightness of the siding? I found a blog post somewhere where they countersunk every single headlok screw in their furring strips... That seems really laborious. Are there any bugle head structural screws that would work in this application? I suppose you could also align the screws so that they're never present at the top edge of a row of siding, but again that seems like an extra headache.
Response to Nick Welch
Nick,
According to "REMOTE: A Manual," "The standard fastener for attaching furring is a pan-head panel-type roofing screw that is long enough to pass through all layers of foam board and penetrate securely into the framing."
If you have any doubts about the structural strength of your chosen screw, you can consult an engineer. But most screws meeting the description provided in the REMOTE manual should work fine.
If I were you, I would experiment with any screw you are thinking of using. Assuming that you are using softwood furring strips (spruce, fir, or pine), I imagine that you will be able to set the screw heads below the surface of the furring strips without any need to pre-drill a countersinking hole. Just drive the screws until the screw head is below the surface of the furring strip. The wood should be soft enough to allow this.
Board and Batten application with fiber cement board
I´m trying to figure out how many times I need to use fasteners for my wall system. I live in a hot humid rainy area, so I wanted a wall system that has a rainscreen and a thermal break.
All measurements are actual (not nominal), and all wood is super dense Quinilla (considered exotic hardwood in the USA) that when dry requires all holes to be pre-drilled, so it´s good to nail or screw when the wood was freshly cut.
Going from the structure to the outside of the wall, I have 2" x 3" studs 16" on center (there will be 2" Rockwool with aluminum radiant barrier on one side in between the studs with 1" of air space in between the almuninum and the foam sheathing), then 1/2" foam sheathing (expanded polystyrene), then 3/4" x 3" wood furring strips also 16" OC over every stud, then 5/16" fiber cement panels (4´x 8´) placed vertically, then 1" x 2" battens every 16" OC over every stud.
So at each stud there is foam / furring / cement fiber panel / batten.
My concern is, if I´m nailing (or screwing) up each of these layers on the same stud, that´s 4 layers of fasteners, and it seems excessive.
My question is, can I just tack up the first 3 layers (with minimal fasteners just to keep the layer from falling during the installation), then lay down a serious 4" SPAX structural screw (slightly countersunk into the batten & covered with wood putty to hide it) through all layers that would give 1.5" of penetration into the stud every 8" OC? That makes sense to me, as those SPAX are super strong. Or would it need 6" OC as it seems to me that cement fiber panels (like vertical hardie panels) require 6" OC? (I could be wrong, it´s been very hard to get a good grasp on this)
One caveat is that where there are vertical joints of the panels, I imagine I´d need to make sure both edges of the 2 panels were nailed in as 1 Spax Screw 8" OC (or 6"?) would only go through 1 panel, or just between the 2 panels.
So what do you think, just 1 main SPAX screw for most of the wall system, with extra nails or regular screws (how long? 1.5" screws?) for vertical joints between the panels?
Thanks so much for any help you can give, I hope that somebody can advise. I work for a non-profit in the jungle area and am trying to build our house to protect us from the rain and hot sun.
Response to Ben Brown
Ben,
My guess is that you are building somewhere without building codes, so I'm inclined to say that you can do whatever you want.
To be more specific: if you were building in the U.S., most engineers would be asking what your plan is for bracing your walls (that is, to provide racking resistance). Choices include 1x4 let-in bracing or plywood installed directly to the studs (with no intervening foam).
Once you've taken care of your bracing problem, your wall may look different.
If your walls are properly braced, and you don't have to worry about hurricanes, you can install the other layers using common sense. If every layer feels properly fastened, it probably is.
Note that putty over countersunk screws doesn't last long in a humid climate. Skip the putty and just use stainless-steel fasteners (if you can find them).
Alt. Fasteners or Fastening Schedule?
is the FastenMaster table the only one out there from which we can discern the necessary fastening schedule?
Their table suggests that vinyl attached to furring strips over 1" of foam is the same as cementious siding over 4" of foam. Given the beefiness of their HeadLOK fasteners, I'm going to say that one end of that spectrum is serious overkill vs the other.
I'm looking to attach vinyl siding to 1x4 furring strips over 2-1/2" foam. 6" HeadLOK fasteners 24" on center seems like overkill, and a pricey means of achieving that overkill.
Response to Dave De C
Dave,
Engineers generally include a safety factor when creating fastening schedules. If you want to deviate from a fastening schedule created by an engineer, it's best to have another engineer give you the OK.
Otherwise, you may discover that there was a reason behind the recommendations in the fastening schedule that you decided to ignore.
-- Martin Holladay
Types of Furring Strips
I would be interested in reading a response to Rob Dickinsens questions
Response to Scott Wilson
Scott,
It took some sleuthing on my part, but I finally figured out that your comment is in reference to Comment #44, posted on January 1, 2011.
Q. "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 climate. Martin -- would you still think pine is OK in a rainy environment?"
A. Yes, I do.
Q. "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)."
A. There are three reasons to avoid pressure-treated lumber: (1) PT lumber costs more than untreated lumber. (2) PT lumber is unnecessary, since untreated spruce, pine, or fir works very well in this dry environment. (Being protected from rain, these furring strips spend their lives in a dry location.) (3) PT lumber requires stainless-steel fasteners, which are very expensive.
Q. "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?"
A. No.
Q. "I am wondering if I can use the same spacing for the TimberLok/HeadLok screws if I use 3/4-inch 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.)"
A. Your plan to contact TimberLok is a good one. However, since 3/4-inch plywood has nail holding abilities and strength characteristics that are at least as good as 3/4-inch spruce or fir, I wouldn't worry.
Treated Lumber
After a decade or so of supplying ACQ lumber which needed galvanized or stainless steel fasteners, lumberyards are increasingly stocking MPS. It is still copper based, but somehow encapsulated so that it doesn't eat nails and screws.
This may help address Martin's third point, but the other two remain.
Response to Malcolm Taylor
Malcolm,
I'm not familiar with MPS lumber. Thanks for the useful information.
Martin
Over the years I have had some real disasters using ACQ. It as particularly partial to eating Galvalum siding panels, which I use extensively. When they came up with MPS I went to a nearby church and lit a candle.
http://www.homebuildercanada.com/2602_deck.htm
Martin-
Great article, as always. Here are a couple updates. FastenMaster website's current page for using HeadLOK screws for this application:
https://www.fastenmaster.com/blog/details/attaching-exterior-rigid-foam.html
which will link to this document:
https://www.fastenmaster.com/tl_files/fastenmaster/download/TER1009-01_20131218_HDLOK_Attach%20Cladding%20Wood.pdf
... now requires 2" framing penetration instead of 1-1/2":
"6.1. Add up the total thickness of furring, rigid insulation and sheathing then select the appropriate length of HeadLOK fastener (see Table 1) that will attach these combined materials and provide a minimum 2" penetration into the wood framing."
Thanks again for all the great content,
Steve
Hi Martin,
I'm doing furring strips on the outside of 10 cm of rigid foam.
On some parts of furring strips, it's only possible to screw into the sheathing (24mm plywood). But where the furring is directly in line with the studs, I want to screw 52mm / 2 inches into the studs.
Here's my worry: Since my interior design is to have open walls (no drywall -- like an old schoolhouse), I need to make sure that my longer screws hit the studs every time. Otherwise not only do I have inadequate anchoring, there will be a screw tip showing. It's the same for the roof with open rafters where I will use 140cm of insulation and 230mm screws (42mm / 1.6 inch stud penetration).
How do I make sure to hit the stud every time? I will transfer the exact stud centers to the outside of the insulation, and I thought maybe if I use a 4x4 piece of scrap wood to line up vertically next to the screw as I drive it, it will help make sure the screw is going in straight (at least on the left-right axis, up down doesn't matter so much).
Also I suppose pilot holes (or clearance holes?) will be necessary for the furring.
Any advice to make it easier and more precise?
Thanks!
BBBGGG123,
Use one of these. You may want to put a larger plywood base on it.
https://www.amazon.ca/Milescraft-1318-DrillMate-Drill-Guide/dp/B014A1Z92I/ref=asc_df_B014A1Z92I/?tag=googleshopc0c-20&linkCode=df0&hvadid=292947999281&hvpos=&hvnetw=g&hvrand=12977624643529258404&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9047862&hvtargid=pla-437180793075&psc=1
Do people really use that contraption for this purpose? Seems a bit much, and I'm not clear how it would work with an impact driver.
BBBGGG,
You probably want to read this article by Rob Myers: "A Timber-Frame House for a Cold Climate — Part 3."
Myers included a photo (see below) of predrilled strapping, with the following explanation in the text: "As with the wall strapping, each screw was predrilled and countersunk using a small jig to ensure that the angle was consistent and the hole was straight. Predrilling the strapping was especially important for the roof, because the strapping and foam are both thicker. If you simply try to drive the screw without a pilot hole, then the slightest variation in grain direction will move the screw off axis and it will miss the rafter. I also inserted all screws before lifting the piece to the roof — it is much easier to work on the ground whenever possible rather than hanging off the roof."
With 2" foam and 1/2" sheathing, is it possible to use very thin furring strips (1/4") that are there only for providing a drainage plane? Siding/cladding would be fastened through the foam with ~3 inch screws or nails.
I ask because we are trying to save a bit of wall thickness.
badmechanic,
Yes, The only downside can be that sheet WRBs (like Tyvek, etc.) don't lay entirely flat, so at that depth they often bridge the cavity, which defeats the capillary gap, and can block air-movement.
Log in or become a member to post a comment.
Sign up Log in