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PBC312
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# Posted: 26 Mar 2025 10:18am - Edited by: PBC312
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Well, about five years ago I posted questions about a small cabin I was planning to build. Work and life got in the way and it didn't happen. Now I'm actually doing it. I've never built anything to speak of but I've learned a lot on this forum and from many hours of YouTube. The cabin will be 12x16. It will sit on two 6x6 skids. I have the skids in place on concrete blocks, ready to start building. The beams are 9 feet apart so there will be an 18 inch cantilever on each side. No plumbing. I'm planning on a gable roof with a 10/12 pitch. Zone 5. This cabin will be rarely used. I have a modern larger cabin already on this property, this 12x16 will be for guests, kids, maybe grandkids some day. And just a fun project to build (I hope). I'll have a bed on the main level but I will also include a sleeping loft. Some questions I'm currently pondering. (1) 2x8 joists or 2x10? (2) Double rim joist, yes or no?
(3) I like the idea of a cathedral ceiling so I was planning on using a ridge beam. Then I realized I had no plan to support the ridge beam. There won't be a third skid in the center of the cabin that could support the weight. So I think I could put in a 6x6 post from the ridge beam to a big header that would run to two more posts centered on the two skids? Or maybe run a 6x6 post to the rim joist, but triple up the rim joists on the 12 foot sides, and add concrete blocks beneath the triple rim joist where the beam will hit it? Or maybe I keep it simple and just use a ridge board with collar ties or rafter ties and scrap the beam altogether. I'd like to find some photos of 12x16s built like this but with the rafter ties exposed (no 8 foot ceiling) so you get the height up to the roof, which I like. Thanks for any thoughts from this esteemed group!
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Brettny
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# Posted: 26 Mar 2025 03:01pm
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2x8 joists should be fine for 12' wide. Double rim joist isnt really needed as it's really just there to space out your floor joists. The idea of a beam in the wall to spread out the load from the ridge beam sounds good..but you could also use the same "header" at the floor level and double/tripple up the floor joists in that area. A center vertical post for the ridge beam would really help. Or you could put in a few wall ties as your alreaty going to have something there horizontally due to the loft.
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DRP
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# Posted: 26 Mar 2025 05:54pm
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Block between joists over the bearing (6x6).
The "always right" cantilever is to extend out no more than joist depth. There is a cantilever table in the floor chapter of the codebook. The support for the 6x6 is something to design, a 6x6 cannot span far between supports. The hazard tool will give design loads "zone 5" doesn't really tell me much about your loads.
https://ascehazardtool.org/
You can bridge over with an appropriate sized header to support the ridgebeam down to the 6x6 girders. Only bridge to the rims if you are supporting the rims, looking for a continuous load path from ridge to ground.
Also remember when cantilevering that any decks or porches will need to be self supporting, you cannot hang on the nails of the rim to joist connection.
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PBC312
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# Posted: 26 Mar 2025 07:17pm
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Brettny, I hadn’t thought of doing a “header” closer to or at the floor level, interesting idea, thank you. If the weather is good this weekend I was hoping to get started on the frame and subfloor. If I don’t have a plan finalized before then I think I’ll install triple rim joists on the 12 foot sides so I have it if I need it. Were you thinking the header (an LVL perhaps?) would sit on top of the triple rim joists? Or that the triple rim joists themselves could function as the header if I joined them together with structural screws and maybe some glue?
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Grizzlyman
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# Posted: 26 Mar 2025 08:19pm
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Alternatively You could also just do the cathedral ceiling and use just a handful of rafter ties instead of ties on every one. With 2’ rafter spacing that’s only 7 interior rafter sets and 4 ties if you do every other. It’s only 12’ wide so it’s not like this is a huge roof and the 10/12 roof will really dissipate any rafter thrust a lot more than a typical 6/12 roof or less. It may not be up to code necessarily but I’ve been in a lot of older cabins where the rafter ties are only on every other rafter- and that’s in heavy snow areas with flatter roofs and much bigger spans- just a thought.
I don’t find that Rafter ties are really that detrimental to the cathedral feel. I was worried about it in mine but now that I’m in the cabin it’s actually nice to be able to hang things on them.
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PBC312
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# Posted: 26 Mar 2025 08:43pm
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Grizzlyman, thanks for this suggestion. If I could get by with four rafter ties this may be the ticket. I’m not looking to complicate this project. Plus I’ll have a loft so the “cathedral” feel is only 2/3 of the cabin anyway. Do you have any pictures of your cabin showing the ties? Are they just regular framing lumber or are they dressed up in any way. Thanks!
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Grizzlyman
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# Posted: 26 Mar 2025 09:15pm
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I’ll look. But they are just 2x8s.
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Grizzlyman
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# Posted: 26 Mar 2025 11:56pm - Edited by: Grizzlyman
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Duplicate
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Grizzlyman
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# Posted: 27 Mar 2025 12:00am - Edited by: Grizzlyman
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Older photo and we have 10’ walls… but still even with 8’ walls I wouldn’t mind the rafter ties.
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Brettny
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# Posted: 27 Mar 2025 07:49am
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Trippled up rim joist wouldnt help because your so far canalever out. Trippled up on the last floor joist would help. The rim joist is the joist that connects all the ends of the floor joist.
You may not need a rafter tie at every roof rafter in your cathedral section. This is a prety small building.
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PBC312
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# Posted: 27 Mar 2025 07:56am - Edited by: PBC312
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Great looking cabin. I’m now leaning toward a ridge board and exposed rafter ties. They actually make it feel more “cabiny.” I have a couple of questions though.
It looks like you have ties on every rafter, yes? Im willing to go every other rafter even if it’s not quite code if the risk is minimal. With a 10:12 pitch and a metal roof it should shed snow well.
If I understand it I would set the ties right on the top plate and there are some structural advantages doing it that way?
In your photo it looks like your actual rafters are also exposed. Do you have insulation on the exterior of the roof? I plan to use that space for insulation.
I just saw another post on here discussing scissor trusses and how they could be made in such a “skinny” way that the poster was able to get a cathedral ceiling and room for a loft with them. That doesn’t seem possible with such a small cabin and 8 foot walls. If I could, I’d consider using them, mainly because they would be fast to install (I will have limited windows of time to build this, and limited help) and it would be harder for me to screw it up.
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PBC312
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# Posted: 27 Mar 2025 08:04am
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Brettny (or anyone), since my plan now is to use a ridge board and rafter ties every other rafter (or, maybe, scissor trusses …) do you think a double rim joist all around is still a good precaution given my 18 inch cantilevers? Would it make a difference if I use 2x8s or 2x10 joists? I see conflicting advice on these joist dimension issues. It’s such a small cabin the additional cost isn’t that much. Thanks.
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Brettny
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# Posted: 27 Mar 2025 08:39am
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Double rim isnt needed either way your building it because you have girders. 2x10 floor joists would make for a really stiff floor. Your canalever really isnt 18in as the outer 6x6 dimentions would be wider than 9' I believe.
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gcrank1
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# Posted: 27 Mar 2025 09:07am
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Do 10' walls!
It will keep it from feeling like being in a little box
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Grizzlyman
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# Posted: 27 Mar 2025 09:36am
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Rim joist doesn’t need to be doubled. It doesn’t do much structurally- just keeps the joists in place until you have blocking and encloses the floor. Double top plate absolutely. I have rafter ties on every one- but my cabin is 22’ wide and a 6/12 roof. Yeah the rafters go on the top plate- as do the ties. This makes the triangle that resists the outward thrust of the rafters and walls. Double top plate ensures that you have a “beam” more or less that is resisting the whole wall bending. That and the rafter ties keep it from spreading. Skip the scissor trusses- that’s a lot of complication for a 12’ wide building- and with a short span I’m not sure how much “cathedral” you’d really have left afterwards. Yes I insulated the exterior of the roof. This isn’t ideal for insulation, but it was a compromise I was willing to make to have the exposed sheathing and cathedral. It performs just fine in cold weather so although it could be better, it’s totally fine.
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PBC312
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# Posted: 27 Mar 2025 09:40am
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I can’t do 10’ walls unfortunately due to a unique site limitation. I think I’ll go with 2x8 joists as long as they are structurally fine. This place really won’t get much use. My 18 inch cantilevers are measured from the outside of the girders, so closer to 21 inches if you measure from the center of the girders.
Thanks to everyone for all the feedback!
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PBC312
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# Posted: 27 Mar 2025 09:54am
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Grizzlyman I love the look of the exposed rafters. I’m going to insulate on the inside for simplicity. I think I’m all set with my plan. I’ll go with 2x8 floor joists, single-joist on the rim, 2x6 roof rafters 24 OC, rafter ties every 48 inches.
Hope to get started this weekend though, of course, the forecast is for a lot or rain. For my floor my plan is to staple and screw 1/4 hardware cloth in each joist bay and put in 2 inch XPS foam board, cut a 1/4 inch short, with Pest Block spray foam to seal it. I’ll screw in some 1 x strips 2 inches down to support the XPS. I saw one person on Youtube add one element to this approach. He cut 5/8 inch OSB the size of each joist bay (painting the ground side with cheap latex paint) glued XPS to the OSB, then set the OSB / XPS combo into the bays, with the support strips set at 2.5 inches. I think this is for greater rodent control? Seems like overkill but maybe it’s cheap added protection against mice and other critters.
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gcrank1
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# Posted: 27 Mar 2025 11:19am
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On my '83-'84 build I used 1" blue dow.
Made a little jig from two pieces of scrap to ride the top of the joists and nail 1x2 strips in the bays.
Cut the dow and dropped in.
After going a ways I put some deck plywood down and had my work surface right there. It was 12x24' and took maybe 1/2 day; more futzy than hard.
30+yrs on there were no issues when we sold it.
Doing it again Id go 2".
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Brettny
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# Posted: 27 Mar 2025 03:33pm
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Carpenter ants can chew foam. Idk that I would use hardware cloth to keep animals out when 1/4in plywood is prety cheap.
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gcrank1
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# Posted: 27 Mar 2025 04:10pm
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Or soffit material?
Stepping back to the earlier posts....since this is beams on blocks and the original cantilevers are hanging out there too far, why not adjust one side to get it right?
Thing is, doing it wrong or right it All Starts At the Bottom.
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PBC312
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# Posted: 27 Mar 2025 05:46pm
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Gcrank1 why do you say the cantilevers are hanging out too far? The beams on blocks are 9 feet apart. The cantilever is 18 inches per side. From my reading it seems like this is easily fine if I used 2x10 joists and fine but close with 2x8s.
The hardware cloth is to keep mice out as I understand it. A lot of posters on here, and Youtubers, have done this, that’s where I got it.
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gcrank1
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# Posted: 27 Mar 2025 06:36pm
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See DRP's post earlier regarding cantilever
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MtnDon
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# Posted: 27 Mar 2025 07:29pm - Edited by: MtnDon
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IRC, Chapter 5
Scroll down to Section R502.3.3
(It is a protected document, so I can't copy and paste)
That is the building code used by virtually every state in the US. Even if you are not having inspections that need passing, the engineering principles of loads on wood joists, etc. remain the same.
Building according to code is a minimum requirement for passing inspections, so can be a good guide as to how to build something that should be sturdy and last a while. Of course, there is no harm in going better than code.
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PBC312
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# Posted: 27 Mar 2025 08:14pm - Edited by: PBC312
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I’ll review this code sectioncloser later tomorrow when I have time, but my reading is since the cantilever will be supporting a light frame wall and roof, I am well within parameters with an 18 inch cantilever with 2 x 8 joists. This is based on me quickly skimming this so for anybody else reading this do not rely on my 30 second review. (Not that there was any danger of that.)
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MtnDon
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# Posted: 27 Mar 2025 08:53pm - Edited by: MtnDon
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Quoting: PBC312 my reading is since the cantilever will be supporting a light frame wall and roof, I am well within parameters with an 18 inch cantilever with 2 x 8 joists
Reading what reference, if I may ask?
Have you had a look at what the snow load rating is? The linked ASCE site tool has very good snow, wind, rain, seismic and other info. Use an address or longitude & latitude or find your location on the interactive map.
(Select risk category 2 for most single-family residential buildings.)
I am in zone 5B, but that only indicates the insulation level. The tool shows 114 lb/ft2 for the snow load, which is very close to the guestimate that I built for in 2008, before this tool was available for free. I checked just now and we should be good to 126 lb/ft2 as long as I used enough nails in the rafter heel to rafter tie joint. 
That is another nice thing the code book is good for; number and size of nails needed to carry design loads such as at the rafter heel to ceiling joist.
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PBC312
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# Posted: 27 Mar 2025 09:35pm
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I plugged in my address in to that ASCE tool. I’m in northeast Iowa. It gave me two ground snow load numbers. First one was 47 lbs/sf. The second was
“for IRC” and that was 33. This assumes I’m reading this right, a big assumption. And I’m doing this while multi tasking about five things, not ideal. Do these numbers sound plausible? By the way, I’ll have a metal roof with a 10:12 pitch.
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MtnDon
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# Posted: 27 Mar 2025 09:57pm
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I'm not familiar with Iowa, but the ASCE tool should be accurate. Not sure how 2 numbers come up; I would go with 47.
Steep pitch metal roofs can shed snow but there is no guarantee. In the decades we have lived in our home with a metal roof we have had three occasions when freezing sleety rain froze to the metal roof and the snow hung on the roof for several days before the weather warmed enough.
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Brettny
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# Posted: 28 Mar 2025 07:02am
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It's a glorified shed..I wouldnt worry to much about a few inches hanging out to much. The whole thing is on blocks also so not a huge deal to add more if you feel the need.
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PBC312
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# Posted: 28 Mar 2025 09:25am
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Ha, that’s true, I try to keep that in mind! I like learning about these things and what the code says but in the end, for this little rarely-used DIY bunkie, I’m fine with “good enough” compromises as long as it doesn’t create a serious safety issue.
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gcrank1
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# Posted: 28 Mar 2025 09:35am - Edited by: gcrank1
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Oh Yeah, reality check! Its a glorified shed....
Fwiw, we have a prebuilt shed, 10x16 with the barn gambrel roof. It provides way more usable space 'up top' than a std sloped roof. I was in sample building of both types and def would not want a 'loft' in a std except for some storage for seasonal stuff.
Mine is a toolshed, etc but I have thought the 10x16 size, or better 12x16, would make a decent small cabin for 2 and maybe the gambrel loft good for kids sleeping (IF you dont mind them doing ladder!).
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