Sheathing questions for tiny house on wheels – help!
I am planning on sheathing both the walls and the roof of my tiny house on wheels this weekend (subject to hurricane force winds while driving down the road). I have several questions about sheathing that I can’t seem to find clear answers to anywhere:
1) Other tiny house builders have suggested using glue and screws for wall sheathing, but nowhere can I find good information about screws that can be used for wall sheathing. The obvious issue is that most screws generally don’t have as much shear strength as nails. I will be sheathing with 3/8 plywood (more reinforcement mentioned below) to 2×4 framing that is no more than 24″ o.c. (see attached drawing) and it looks like code calls for 6d nails (code doesn’t apply, just using for reference). Should I stick with 6d (or 8d?) ring shank nails , or can I use deck screws or some other kind of screw? (and what about the roof sheathing?)
2) I was planning on running my sheathing vertically to minimize seams between studs and also because I read somewhere that it provided stronger shear strength. However, I just had to special order 3/8 panel clips with a minimum of 250 (so I have plenty of them) and it seems like running the sheathing horizontally and staggered across different studs would be stronger. For reference, the wall heights are right side 9’+, middle 11′, left side 8.5′. What is the best way to run the sheathing in this situation?
3) I am planning on running a Simpson Strong Tie metal strap bolted to the trailer at bottom right and nailed bottom plate, every stud, top plate, and rake rafter at top left to reinforce for the prevailing wind from the right. It would obviously be stronger to do this before sheathing, but I am concerned about concentrating condensation inside the wall cavity, so I’m thinking I will put this metal strap over the sheathing and house wrap. Insulation will be Roxul with vapor barrier on the inside, climate zone 6. So the question is: under the sheathing or over the sheathing and house wrap?
I would greatly appreciate any good information or input on all of this.
Thanks,
-Ryan
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Replies
Ryan,
Lots of overthinking going on. Use some construction adhesive and 6d or 8d ring-shank nails, and don't worry so much. Run your sheathing horizontally or vertically, whatever you prefer. It's a tiny house, and it's going to be fine -- even with your hurricane-force winds.
I would install the Simpson strap before the sheathing if I were you. [P.S.: Malcolm gave better advice. Install the straps after you install the sheathing but before you install the housewrap.]
Ryan,
1- Use 2 1/2" ring shank nails to attach the sheathing. Space them at 6" o.c. and be very careful not to overdrive them. 4" o.c will give you better strength, but with 3/8" plywood there will be no material left if you nail that closely.
2- Run your sheathing horizontally. If you are still worried about strength once it is sheathed, you can block the seams. i wouldn't though.
3- The straps are better placed on top of the sheathing. Run the WRB on top. Use a gun rather than hand nailing both the sheathing and Simpson connectors. Much less splitting that way.
Hey Malcom,
I did the same thing here on my tiny house. I ran horizontal sheathing on 10 foot walls. I didn't install any blocking anywhere. Just added a lot of diagonal strapping. Curious why you say here to Ryan you wouldn't block the seams? I am just debating if I need to or not. Your info has been helpful. Do you not think the blocking adds much strength or is that important?
Thanks,
Alex
Thanks for the quick replies guys.
Martin - I appreciate the advice as I do tend to overthink; however, i have to ask: you don't think that the Simpson strap might create an issue with concentrating condensation at the strap inside the wall cavity?
Malcom - Is the condensation issue the reason that the straps are better placed on top of the sheathing? And what is your thinking behind putting the WRB on top of the strap rather than the strap on top of the WRB?
Thanks again guys!
Ryan,
I'm a consultant with and insurance company. We deal with large structures all over the globe, including in hurricane areas. I can tell you from our reach and experience, the most critical detail here is to ensure the buildings internal air boundaries are not broken. Once a window breaks or there is a large hole in a wall, there is not much that will prevent the pressure that is the exerted on the underside of the roof. In large structures the roof will lift off and usually the rest fails.
I would be less concerned with wall sheathing being ripped off and try to ensure you have good storm windows and door. Studies show there is not much that standard wooden structure can do when a 2x4 is launched through a wall at 100mph.
Ryan,
My structural engineer always specifies that the straps penetrate both the sheathing and studs underneath to tie the whole thing together.
Straps, nails, bolts - all structural attachments - are generally placed behind the WRB for a couple of reasons. First because you need to see what you are connecting them to. And also because of the normal sequencing of construction: Build the complete structure, them wrap it. Condensation simply isn't an issue.
Martin is right. These types of small structures simply don't have the forces exerted on them that larger house do - even when towed down a highway at beak-neck speeds. They are extremely robust and easily resist the loads. You have a much larger chance of tipping it than losing any part of it to winds.
It's worth remembering how comparable mobile homes are built. RVs and trailers have incredibly fragile structures and skins and yet generally don't fly apart - although for some reason they do seem to have a propensity to attract tornadoes.
Thanks, Malcolm. I withdraw my comment on the Simpson strap.
Ryan: Follow Malcolm's advice and install the straps after the sheathing. No, you don't have to worry about condensation.
Ryan,
I would consider going to 1/2" sheathing on the roof. 3/8" doesn't give you very good holding strength for the metal roofing screws (all the manufacturers I'm familiar with spec 1/2" as a minimum sheathing thickness). And with 1/2" you don't need panel clips. The clips are there to help align the edges of thin roof sheathing (but are of no use on walls).
Modular s glue sheathings for transport issues.
Thanks again for the input guys!
Malcom - I was actually planning on using 5/8 plywood on the roof as my supports are going to be 24" o.c. and it is a low slope roof. Do you think I could get away with 1/2"? As far as panel clips on the walls go, don't you think they would help prevent the plywood from warping as much at the edges? I was also thinking they would be convenient for creating the 1/8" expansion gap between the sheets (and I already special ordered them).
Ryan,
Apart from the extra weight of the sheets, working on a 5/8" roof deck, rather than 1/2", is an absolute treat. Your code does allow you to use 1/2" if you want, remembering that unlike most other roofing, metal adds significant structural strength.
The H clips won't do any harm.
So is 3/8 plywood ok for 24oc wall sheathing? I am working on a tiny house as well. Could use the extra couple hundred pounds of weight I would save with 3/8 vs 1/2 inch wall sheathing.
However definitely want good structural integrity for on the road. I did add a lot of bracing..
Curious if you all think the 3/8th's wouldn't be a big deal. ?
Thanks
Alex
Alex,
3/8" sheathing is a bear to work with. Naturally wavy, no holding strength for fasteners. I'd avoid it if possible.