Girts - best attachment method?

[PlicketyCat]

Post-framing my "shanty" -- 16'x24', with three 8' bays. My posts are 8x8, which is way bigger than I need for structure, but the right size for the depth of wall insulation I need. I ran the numbers and don't need any studs in that span and don't want to deal with stud-framing anyway. So have decided to use horizontal girts (top, bottom & mid) for rigidity and a nailing surface for sheathing. Figured I'd use 2x4's for the girts, just trying to figure out what's the best way to attach them for structural support, weather-tightness and insulation.

Would it be best to:

• Face nail the girts flat (4" out) to the outside of the posts and shim the posts out flush for the cladding? (seems like a waste of lumber)
• Face nail them flat, but let them into the posts with notches so the face is flush for the cladding? (a little more work, but not as much waste and doesn't eat up too much insulation space, but is it sound for bracing)
• Toe nail them on edge (2" out), between the posts? (seems more sound for bracing but really eats into my insulation cavity)

Also wondering if I'm still going to need diagonal bracing if I use any of these methods? (Wind Cat B/C, max 60mph, but Seismic D1)

And what to do about the interior side of the wall... still need some sort of nailing surface and support for the inner sheathing. More girts? (might as well stud frame if I'm going to use the same amount of lumber). 

Biggest thing is not creating (m)any thermal bridges in the walls and getting as much insulation as possible in there, as consistently as possible, so I don't get cold spots. And, of course, not using way more lumber than I actually need to for structure and insulation.

[moonhill]

PC, what are you going to use for insulation?

Tim

[Jim_Rogers]

One of your first decisions is which way is the siding running? Up and down or left and right. This will tell you how your outer girts will be placed. As I read your choices I'd say you have decided to have your siding run up and down, as you're talking about attaching the girts to the posts.

Well there are these ways to attach girts:



Next comes the same question, which way will your interior cladding run? Vertical or horizontal. This again will determine how your girts will run. If you're going to do the same thing run them vertically then you'll have to figure out how to deal with them at the top and bottom where they touch the plate/ceiling or floor/sill.

When not wanting to create a thermal bridge then one set of studding is done outside and one set is done inside with a gap between the studs. And these studs are not necessarily aligned with each other.

If you ran the outside girts outside of the posts and then put on vertical siding there will be a gap between the siding and the post, which I think you have mentioned. Instead of filling this gap with wood; you could stuff it will some insulation and thereby break some of the thermal bridge between the post and the outside.

Another consideration that you need to think about is what type of insulation are you going to use? If you're using batts that's one thing, but if you were to use sheets of ridge foam you could put them on over the girts and then put the siding on. This would make the wall thicker and eliminate any bridging at the posts. If you did use sheets you could flush attach the girts.

Just some things to consider.

[shinnlinger]

Nice post Jim (as always)

I always like windbraces, but they can mess with your insulation if you are infilling the wall.  If you are putting plywood on the exterior you may cover your shear concerns that way, but it is your seismic issues that may have me talking with an engineer, but you probably be OK with 3 or 4 horizontal girts with plywood attached.

If you go that route, I can see the plywood being a nice surface to attach your exterior siding, but dont know how you will attach your interor wall once the insulation is applied/installed.

Dave

[PlicketyCat]

We'll be using dense-pack blown cellulose... it's the biggest bang for the buck (we have to have min R-24 in the walls and R-32 in the floor/roof) and will flow in around any weird framing. Rigid foam is a bit easier to work with on large spans and better R for the inch but won't flow around framing and is way $$$. Batts require too much framing and don't have as much R as cellulose unless you get the $$$ stuff. Blown fiberglass is not an option since hubby is extremely sensitive to fiberglass and I'm not doing that part of the job all by myself (again!) :D

I intentionally designed on a 4x8 grid so it really doesn't matter which direction I run my cladding, as it'll fit evenly in either direction... so in the end it'll come down to which direction the cladding can be properly supported & attached between the posts (and to the posts) with the minimum amount of supplemental (non-structural) framing.

We'll be using 3/4" CDX ply, then weather barrier, then probably T1-11 or similar on the outside... the double diaphragm is what the structural engineer at UAF recommended for our seismics even though a single layer is normally enough for most walls. Inside we'll have 8 mil vapor barrier and thinking ACX T&G ply, probably 3/8 or 5/8, since it's sturdier than sheetrock (and you don't have to tape and mud it -- bonus!). If we go with T&G on the inside rather than plain, we'll probably run it vertical because too many horizontal lines make me go buggy and tend to make a room look squat (not what we want in a tiny cabin).

Outside, I think if we run the CDX horizontal, and the T1-11 vertical, we should cover our shear issues and not end up with water pooling in the T1-11 grooves & joints inviting rot. Inside shear isn't as much of an issue, we just don't want the wall to bow and gap (horizontally or vertically) because there isn't enough supporting it from the backside.

The girts (or studs) don't necessarily have to be 2x4s, they could be 2x2 or 1x6 or whatever will provide the proper rigidity, as long as they are price comparable. I think either half-lapping a 2x4 girt flush (2" out) or housed butting them (4" out) flush would give the best support without weakening any of the members or eating into my insulation too much.

[shinnlinger]

 I say the housed butt joint, the second one down in Jim's pic, will serve you well.  It will lock the 2x4 and is the easiest of the 4 to make IMO.  I would  run the cdx horizontal and stagger the interior ACX with the the t-111.  I assume you will run another 2x on the inside face to hang the ACX.

[PlicketyCat]

We're figuring at least one girt at 48" for center/edge support no matter which way the play is oriented and probably another at the top and bottom at least on the inside (outside we can nail directly into the sill and header beams). If we're running the ACX vertical, we might also put in a vertical stud at 48", just to shore up the seam.

I agree, house butt joint only requires me to make one cut... less work is much goodness

[Thehardway]

Plickety,

Jim's drawings show a number of methods for attachment all of which are good for bent style timberframing.  There are a couple of issues you might consider when choosing.  The more uninterrupted horizontal members your frame has the more rigid it will become.  Lots of discussion has been had about traditional vs. bent style framing for this reason. Modern day bent style framing has very few continuous members. If you can incorporate continous sills, plates, or girts it does a lot to strengthen and make things more rigid and square.

Unless there is a specific reason for doing so, (such as you can't get 2X in lengths longer than 8') it would IMHO be better to use 16' (24" would even be better if you are cutting your own material) 2X for the girts.  Alternating the joints over the 24' span and using a half lap at the post will give you a very rigid and square structure to attach your horizontal CDX ply to.   I would also leave the lap joints 1/2" proud at the posts.

Why leave them  1/2" proud?  Because as Jim mentioned, it eliminates most of the thermal bridge created by your posts.  You can now cut a strip of 1/2" ridgid foam board to place between the sheathing and the post which will serve to break the thermal conductivity and to seal the seams between panels as well.  Where you are building I could see heat loss through an 8" post if there is no thermal break depending on the type of wood you use.

You might also want to consider a spray in place polyurethane insulation.  You get a much better r-value per inch, it forms a airtight barrier, is fire resistant, and will lock all the construction together like a giant styrofoam shipping container.  They are using it a lot now in high wind areas like Florida because of the way it adds structural strength.  Added bonuses are it does not settle, rodents do not typically like it, and it goes in fast expanding and filling all gaps or cracks.

4" would give you a great insulated envelope and you could build shelving into the remaining 4" of wall.  Down side is the cost.

We are feeling the cold here is VA this year,  a high school gymnasium just had its roof collapse from snow load and DC has had almost 60" of snow.   ;D


   

[moonhill]

There is a fine line between girts and strapping.  Pole barn construction has been chatted about recently and this sounds like it fits that category very well.  I want to second Thehardway's post, not that PC method won't work, I just see some improvement in structure and efficiency, yup, at a cost. 

I myself would skip the posts altogether and just plank up the wall with vertical 2" planks with pegs inserted in the edges acting as sheer and foam the exterior with 4'x8' sheets, strap and side it.

Tim   

[PlicketyCat]

We can get lengths longer than 8' since we're purchasing froma lumber yard that mills their own. Main issue is that a 16' or 24' is about 1.5x the cost per LF than the more standard 8' or 10' and MUCH more difficult to get back to the site. But I do see how having continuous members has it's advantages. Would mechanical lamination/splicing acheive the same effect? If I scarfed or lapped the girts together and pinned through the joint into the post?

I would love to use spray poly for all the reasons mentioned if we could 1) rent the machine, 2) find the DIY components for sale up here, and 3) afford it. There is no way we can afford to have an insulation specialist come out and do this for us... the cost of travel expenses alone would kill the budget. When you live 4 hours from civilization, labor and components is often cheaper than travel and transportation!

If we could do poly DIY, then we wouldn't be making the walls & ceiling so thick and could use less expensive lumber sizes (and almost break even on the cost). Even using rigid foam would make the walls slightly thinner, but not enough to jusitfy the price hike. I've had good experiences with dense-pack blown cellulose and I can rent that blower, buy the bales to do it DIY, and get it to my site without special ordering or breaking the bank.

We'll have the 3" foamboard from the tent that we can reuse for awkward places that would be hard to get at with the blower nozzle after framing and sealing, but we're hoping to save most of it for the bath house ;)

[Thehardway]

Two-part polyurethane foam is available in DIY form.  One brand is called Handi-Foam and can be found at  www.foampower.com   it can give you an R-24 in a standard 2X4 wall application.  I have not used this particular product and this is not an endorsement of the product, it is just to say that it is available for DIY and can be ordered through the mail.

Not sure how to tell what the cost is as their coverage calculator is not working.   I am sure there are other brands out their as well.  I have been told temperature is critical for the two part mixtures to work properly.

You may be better off to use what you are experienced with and is readily available locally.  Just thought I would throw the idea out there as it would be rather slick.  Good luck.  I enjoy reading your blog.

[PlicketyCat]

I haven't been able to find any local suppliers for the poly or the sprayer, although I did notice that some were available online for DIY. Most of the time it's shipping & handling that's going to kill us with ordering stuff, but unless it comes USPS then we'd have to drive into Fairbanks to pick it up at the UPS/FedEx depot anyway since no one delivers out here. Even if it can be sent through the mail, if it's big or heavy we might still have to make additional arrangements for the mail plane to deliver it (i.e. extra $$$ on top of postage).  Sometimes the practical logistics of living in the bush really interfere with cool ideas !