Wood sidings such as clapboards aren't nailed into the sheathing, but rather through the sheathing into the wall studs. One avenue would be for you to sheath with osb as planned, then run your foam panels. The sheathing will keep the clapboards from "cupping" or "bowing" inbetween the stud cavaties whereas with just foam, you would have that "cupping". You will need fasteners long enough to go through the osb, foam, and into the studding at least one inch. I would go the expense to lay your studding out 16" o.c. but that is just my preference as i rarely put any members 24" o.c. If you go with 24" centers, you might want to consider using 5/8" drywall on the walls vs 1/2" to prevent "waving" of the wallboard on the inside of the exterior walls or any where where you have a 24" o.c. layout.

Let's please keep it on-topic. The drywall and studs are irrelevant to my question, and have already been taken care of.

The question I need help with is about the technical details of how to use rigid foam exterior insulation panels with OSB sheathing and wood clapboard siding.

i used foam sheathing instead of osb on my last build then sprayed poly foam inside. i will not do it that way again. you are better off just using sip walls to begin with.
i agree with seirra about 24 on. its not worth the small savings you get.

Once again: I did not ask for advice/input on the stud spacing. I asked for advice/input on how to install the rigid foam insulation panels.

The walls are 2x6 construction with 5/8" drywall on the inside and 7/16" OSB on the outside, with wet-sprayed cellulose in the cavities. That's a DARN solid wall right there, and even with 24"-o.c. stud spacing it's far more solid and structurally-stable than a standard 2x4" wall with 1/2" drywall and 16"-o.c. stud spacing.

So, please, back on topic -- what I need help with here is learning how the sandwich of the OSB sheathing, rigid foam insulation panels to prevent thermal bridging, and wood clapboard siding, goes. Any advice on THIS, from folks that know and have experience with it?

FWIW, here's the blog/photos/construction details/layout/plans for the house: http://BuildingInTheSouth.blogspot.com/

Here is a link that might be useful: Southern traditional home building experience

Ok, I'll bite..... "how do you install to install rigid foam insulation panels?" Around here, rigid foam is typically installed on exterior applications with a cap nail gun.

If, on the other hand, you are looking for more specific details regarding the installation of rigid foam and clapboard siding you may do well do pay special attention to the comments of sierraeast -- who around these parts is known to know a thing or two about sound construction techniques.

What I believe sierraeast is correctly alluding to -- is that your proposed design -- sheathing, foam, siding -- is not altogether uncommon in clapboard siding installations. However, the 24 oc spacing while not structurally problematic, is not standard for clapboard and MAY lead to complications with your siding and drywall installations.

My advice would be to pay special attention to siding fasteners as sierraeast proposed. Also, you'll want to carefully consider how you want handle openings (such as windows) and flashing details given the added thickness. We used 1/2 inch plywood, 1/2 inch rigid foam, and then used fiber cement as siding (comparable to your wood clapboard). We installed housewrap atop plywood, windows installed next, then rigid foam was installed and caulked at the seams.

I might suggest reading some of the material at buildingscience.com where they discuss alot of these very issues in great detail.

Best of luck!

Thanks niff and sierraeast for your replies, and please excuse me if I sounded snippy. It is proving incredibly frustrating to get down to brass tacks and get the real info when it comes to insulation -- the marketing departments of the fiberglass manufacturers are ever-warring with the marketing departments of the cellulose manufacturers, and the rigid foam manufacturers, and the open-cell foamed-in-place foam manufacturers, and the closed-cell foamed-in-place foam manufacturers, etc. ...

And it's hard to know whom to trust, since the Internet is anonymous so you don't know who has a vested interest in giving a biased answer and who doesn't, and who's a rep from the marketing department of a company posting on here or Wikipedia or elsewhere, etc.

It didn't occur to me that by going with 24"-o.c. exterior studs, that would mean fewer places to nail in the clapboards, and thus they'd have more ability to warp. That was a good call by the both of you, and I'm going to edit my plans to reflect that.

So let me make sure I've got this right -- it would be okay to nail 4'x8' OSB sheathing panels to the outside of the studs, then 1" rigid foam panels to the OSB, then put the wood clapboards on top of the foam panels and have the nails go THROUGH the foam panels and into the studs?

Here is a link that might be useful: Blog about the construction of my dream home

Thanks for the reply AND ESPECIALLY THE PHOTOS! (I'm a very visual person)

(1) What was the cost of doing this? How much more was it than just nailing the clapboards to the OSB sheathing would have been (in other words, no foam panels and no strapping)?

(2) What is the advantage/are the advantages of the strapping? Does that air-space present any issues with moisture infiltration behind the clapboards?

We, too, did the rain screen/air gap design as well. One thing we did in our installation in addition to vertical furr strips/strapping was to run strips of cor-a-vent in key locations (such as at window heads and at the watertable). Coravent provides both ventilation and a bug screen in a single design. You can read more about the cor-a-vent design at their website at coravent.com (I believe).

In regards to cost all said, additional plywood for furring, coravent, and rigid foam all added about $2-$3K to our job. Oh, and we put felt paper on the furring strips at the joints.

As to the strapping, this design is referred to many as a rain screen design. The air gap creates a ventilation gap that specifically allows any moisture that does get in the ability to dry. This design is thought to extend longevity of the siding and its paint. And yes, all the details can get pretty tricky if not well thought out.

For more on rain screen design, Fine Homebuilding's Exterior Siding book has a whole article that walks through the design (with a clapboard installation I recall). Also, another resource you might find is to do a search on the Delores House done by Rollie ? who steps in here now and then. He details step by step in a photo journal how he constructed a house with a rain screen design. I think if you google delores house you may find it.

That Delores House photo-tour was very informative. Thanks!

Question: how thick should those strapping strips be? 1/2"? 1"?

Much debate on furring strip thickness required to be "sufficient for rain screen design", but from everything we have read, it seems the general concensus is 3/8" or greater will definitely work. We used 1/2" cdx ply as it is the exact same thickness as the cor-a-vent siding strips used at the bottom and top.

see the cor-a-vent website for installation instructions. I think they make the strips in 3/4" as well, but 1/2" is plenty IMO.

Rollie's Delores house lives on!

where are you building pierce?

I am building in BEAUTIFUL Dade County, GA

For more details of the house and the move, please check out the blog! http://BuildingInTheSouth.blogspot.com/

Here is a link that might be useful: Blog about the construction of my dream home

i love it when wanabe home builders ask for advice and then when experienced builders give wanabe home builder, who by his own admission doesnt know much about building, advice he gets snippy.
i am telling you as an experienced builder who has already done what you are attempting to do that you can more easily and probably for less money accomplish your goal with sip walls.
using an inch foam sheathing sounds easy but you run into all kinds of problems with window framing and window and door jambs and having a flat nailing surface for flat siding. been there done that. never again.

Since I'm in the design/planning stage of my dream house, I'm reading this with great interest. Although the OP had one specific question, others might be interested in the whole wall structure. My design incorporates 2X6 wall framing as well, but I'm leaning towards SIP's, if I can afford it.

I've been staring at my monitor for a half hour deciding if I wanted to write this.
This is one of the most wonderful forums with the best group of people on the web. I love reading the wonderful blogs many of our members keep while building their homes and have quite a few saved for future reference. So, of course , I settled back to read what I assumed would be a wonderful journey to a wonderful home in that gorgeous Georgia country. It's taken me this long to pick my jaw up off the floor.
I would encourage you all to read the OP's blog and decide if this is someone you WANT to respond to. By the second paragraph of his first blog entry, I was stunned-by the end, I was sick to my stomach that this could exist in 2008.
Pierce, I am what you so tactfully described as one of "those carpet-bagging Yankee bas***ds" that dared to move South from New York and desecrate your Southern culture. Very fortunately for my family, the TRUE Southerners we have met since we moved here 3 years ago, have been welcoming, gracious and have made us proud to call the South our home. For the record, you have NO idea what it means to be Christian.

Now I really feel sick. The following is what I recieved in my email from preacher Phillips. His blog has now been edited to remove references to his desire to live in a "white" county. Now I think I'll join MightyAnvil

Sweetheart...you live in the People's Republic of Chapel Hill, and you think you know what the South is really like? Seriously? You live in a city -- but not just any city, a college town known far and wide as one of the most liberal in the entire South...and you think you're in the real South? That would be like spending a week on an oil rig off the coast of Texas, and saying you thus know what Saudi Arabia is like.

Why don't you troupe on up here to Vance County sometime, where we still have the Klan listed in the phone book. Yeah, in 2008. (252) 492-7000.

You're just a God-hating, Bible-defying Jezebel with a bad attitude and a selfishness complex. Being an ordained preacher, www.pierce-phillips.com, I beg to differ with you that you know the Bible better than I do. Have you ever even read it cover-to-cover and learned every verse? Or are you just "buzzword-compliant"?

I also read your blog and just wanted to make a small correction for you. The house you are building does not appear to be shotgun house. Shotgun houses have all of the rooms lined up in a row with no hallway. The houses are narrow and the rooms are lined up single file. Your house does not fit this. You might want to do a little more research on this before you continue to tell everyone that you are building a shotgun house.