I’m designing a modern-style shed to be used as a home office. It’s small enough to avoid permit requirements, but I want to adhere to code and best building practices so it will live long. This is in western Washington state, where seismic activity isn’t unheard of. Wind loads should be relatively minimal.
I’ll be using 2×6 framing at 24″ OC (going for an “advanced framing” strategy) and a pier & beam foundation with 2×8 joists. The interior framing will remain exposed (no drywall), but I will insulate the exterior with 2-4″ of rigid foam on top of Zip System sheathing, then a rain screen assembly.
I have 2 questions about the sheathing.
1. Is vertically-oriented sheathing OK, or should I run it horizontal? From research, I gather than horizontal is preferable for shear strength due to the 24″ OC stud spacing (each panel lays on 5 studs instead of 3). Is that accurate, especially considering seismic possibilities? My only hesitation is that I wouldn’t mind avoiding blocking.
2. Is it adequate for racking strength and uplift resistance to run the sheathing from the bottom to top plates of the walls, or should I extend it below the bottom plate to fasten it to the rim/end joists? If the latter, how far – a few inches below the bottom plate, all the way to the bottom of the rim/end joists, or a lip below the rim/end joists to maximize runoff?
Replies
I've never seen any preference for horizontal sheathing over vertical. With sheathing all edges need to be nailed. If you run it horizontally you'll have to run a row of blocking at 4'. This really doesn't need to be nailed to the studs but only to the edges of the panels so flat blocking is OK. You don't need to run the sheathing over the rim joists if you have adequate hold downs from the edges of the panels* to the foundation.
*A shear panel is not just a 4' section of wall but the wall that is continuiously uninterrupted from top to bottom ie each section between windows or doors. If you have a 10' section of sheathed wall you need hold downs at each end not every 4'.
Thanks for your input! This all makes sense, and gives me a few new concepts to research.
I'm familiar with hold downs on a concrete foundation, but I haven't encountered them in the context of shear panels and floor joists. Any chance you could point me to a specific product(s) that's typically used for that purpose so I can better understand? I've been searching through the Simpson catalog, but so far, everything I'm finding assumes a concrete foundation.
Or, would you be describing Simpson LTP4/LTP5?
https://www.strongtie.com/resources/product-installers-guide/ltp4-ltp5-installation
Looks like there are also structural screws to secure the sill plate to the rim or end joists:
https://seblog.strongtie.com/2016/12/design-sole-plate-rim-board-attachments/
I assume that your piers are poured concrete in the ground with some kind of footing. The edges of your shear panels should have at least a double 2x boundary member, a king stud and trimmer at the windows and doors, two or more studs at the corners. Just use a hold down strap from this boundary member into the concrete.https://www.strongtie.com/straptieholdowns_holdownsandtensionties/lsthd_holdown/p/lsthd. If your piers are just precast blocks set on the ground then build the hell out of the shed so that if it falls off these you can jack it up and put it back on.
Where are you in Washington?
Thanks again! Very, very helpful - I appreciate it.
The latter is the case - I'm using TuffBlock plastic deck blocks, which have a maximum spacing of 59" OC.
https://cdn.shopify.com/s/files/1/1724/7813/files/TuffBlock_Install_Guide_2.pdf
The shed will be approx. 12' x 16', so 3 blocks along the shorter side by 5 blocks along the longer side, with a ~1' cantilever all around (see plan view attached).
Idea is to set short (~12") 4x4 posts on the blocks, set doubled 2x8s on the posts as beams (connecting w/ Simpson BCS2-2/4Z caps), then 2x8 joists with a single rim at 16" OC across the beams, then 23/32" AdvanTech subfloor. (I was flirting with 2x6s as joists to save a little money, but the advice I gather seems to be 2x8 minimum for an acceptably stiff floor.) I'm still researching cross-bracing strategies for the posts and beams, but I'll reinforce them pretty thoroughly with 2x4s.
When you say double 2x boundary members and two or more studs at the corners, would a normal California corner satisfy that with perpendicular adjacent studs at the corners, or is the idea to sister two studs at both ends of the framed shear wall? Does that only need to apply to vertical members, or do I need to double top and bottom plates as well?
Since there won't be concrete, would I just maybe use comparable heavy-duty Simpson straps like HRS416Z to tie these doubled members to the rim/end joist below (underneath the sheathing, I assume - or do I just bend them slightly to tie the exterior sheathing face to the joist)?
I'm actually expecting to build up to 3 of these sheds, and they'll go on a few acres we just bought on the NE side of Sedro-Woolley. It's a fairly densely forested lot with some gorgeous scenery. We'll need an engineer for the house eventually if you should know anyone in the area (or are one)!
Pretend that you are building a tiny house that will need to be moved to the site and build accordingly. Strap the walls to the floor and the roof to the walls.
Although I never really lived there, I did a considerable amount of construction on Whidbey Island. I was a licensed contractor in Washington for a few years. It's been so long that I don''t have any contacts any more.
(Replying to this comment since I can't seem to reply to your latest!)
Gotcha, thanks!
So basically, what's most important is that the envelope (joists, walls, rafters) is very structurally integrated and rigid? And of course I'll cross-brace the beams and posts and take all practical measures I can, but I shouldn't be too surprised if the whole thing slides off the posts in an earthquake - goal is really just to keep it from racking or pancaking?
Whidbey Island is such a beautiful place. My dad fell in love with it a few years ago when he first visited, looking for places to move after he retired. He and my mom just moved up there a year or two ago to a house they had built on the coastline on the outskirts of Oak Harbor. That's a big part of why my wife and I are relocating up there. I don't remember the builder's name, but I would imagine you know of him - he's also a long-time builder out there with a great reputation.
Thanks again for all of your help - I truly appreciate your input!