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cluelessinKY
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# Posted: 7 Oct 2023 16:46
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Hello all! I’ve been pouring over this forum, forestry forum, country plans forum, and codes for a month as I try to learn, as quickly as I can, how to build my first structure. My partner and I are trying to build some sort of livable (insulated) shed/cabin that we can live in for months or years while we try to build a sustainable farm in northern KY. We may try to plumb for water, but will def wire for solar. (I know RV is prob smarter, it’s just not what we want.) I respect your advice as well as your time, so I’m going to try to be brief. I’m really just trying to get a second, third, etc., set of (experienced!) eyes on our build idea before we throw ourselves at it and try to get it livable by January. (We have purchased the country plans, some shed plans, and the “cozy cabin†plans from Bailey Line Road, but our circumstances won’t allow us to follow any of these to the letter, so we’ve modified some.) Here’s what we’re thinking:
12x16 with 9:12 unvented gable roof/cathedral ceiling with spray foam insulation for unvented roof to work. (A well-respected building science professional wrote a compelling article suggesting venting roofs in mixed-humid climates is unwise, which is why I made the unvented call.)
2x8 rafters with 2x10 non-structural ridge board, hoping for 2ft overhang in all directions, gotta check that rafter span again.
Roof tied on with parallel-running, 2 sistered 2x8 ceiling joists acting as rafter ties, forming one small and one larger loft on opposing sides of building. All but one rafter has a ceiling joist rafter tie (one joist omitted to make room for ladder).
2x8 floor joists sit on top of girders, connected in some way I haven’t nailed down (pun!) yet
2 girders, girders are 3 laminated 2x10s, no splices(joints) in them, they run the full 16 long. No girder down the center of the cabin.
Girders sit on piers—4 each side, cantilevered in by 12†on all sides. Country Plans does this 2ft on all sides, but I wanted to stay closer to the rule of cantilevering only the depth of the girder.
The foundation has been the absolute most difficult to figure. Expansive clay soil based on websoilsurvey, 1500psf. Frost line said to be 32†though codes only requires 24â€. Approx building weight 19,200lbs. Ground snow load 20, ultimate wind speed 115. Weathering of concrete is severe (can’t seem to find exactly what that should inform regarding design).
So I settled on piers.
Piers are either option 1 or option 2:
Option 1: 6 (3 each down both long sides) 28†x 28†Square Foot footers with Sonotubes. (Wrap sonotubes with something that helps the frost not get to them…read that somewhere.) Dig to 36â€. Square Foot roughly 16†tall, Sonotube 20†below grade and 28†above grade, connects directly to girder with some unknown Simpson connector, making building 28†off ground. No posts.
Option 2: 8 precast EZ Tube piers, 4 each down both long sides. (Need 8 instead of 6 for precast because the base diameter is only 22â€. The square footage of 22†diameter works for only 6 piers on my build, unless I beef it up by 50% per pier to account for possible concentrated loads, advice that was given on one of these forums by someone who seemed very knowledgeable. If I need that extra 50% beef up, I have to add another pier per side, increasing my total to 8. That makes it where a 22†diameter base is more than enough to cover 50% MORE than it needs to cover with the straight math of my building weight divided by my soil psf. Phew.) To the best of my knowledge these EZ Tubes shouldn’t stick out far above grade, so I’d use 6x6 posts to connect pier to girder, raising the building approx 24†off the ground. In this instance maybe knee bracing (correct term?) between post and ….girder? floor joist?….could help lateral force issues.
Why don’t I just do a full perimeter footing? To be honest, I have studied this pier thing so hard and we have to start building immediately, and I just don’t know if I have time to figure out if a full perimeter can work for us. (I also don’t want a crawl space. I plan on putting no utilities under the house on this build, just hoping the elevated pier/post will help moisture issues and lessen radon exposure.)
I have soooooo many questions. But for now, if anyone could just holler if some or all of this sounds terrible, I’d be very grateful. Thank you guys in advance.
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gcrank1
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# Posted: 7 Oct 2023 20:59
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12x16 will be a tight space for 2. Yeah, it has been done but upsizing wont cost all that much more and will be, imo and e, so much better.
I say this from having had an 8x12 ice shanty/bunkie, a 8x12 diy camper from a 'bread truck', a 12x24 cabin build with a 12x12 stand up in center loft and our current prev owner built 16x24.
We built the 12x24 in '83-'84 mostly from repurposed lumber from an 1897 barn and had it for 34 years.
It was my design and build using a modified post and beam style to best utilize the barn beams in multiples of 12x12 interior spaces; ie, 12x12 kitchen/table, 12x12 living room (wood stove between) and the loft the 12x12 bedroom. It worked out very well for the 2 of us and occasional guest or two.
Thing is that the available space becomes very tight once you get the 'stuff of living' inside and spread about.
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ICC
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# Posted: 7 Oct 2023 21:42
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Foundation... A concrete pier design with the beams connected directly to the top end of the cocrete piers is vastly superior to a foundation using an intermediate wood 6x6 between concrete pier and the beam. That is simply another point for a lateral movement failure.
I second gcrank1's comment on 12x16 size w 2 people, especially for extended periods.
Lofts are always hotter than the main lower floor, so if one level is a comfortable temperature the other is too cool or warm. IMO.
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gcrank1
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# Posted: 7 Oct 2023 23:06 - Edited by: gcrank1
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Agree on the loft as a bedroom, Id not do it again except for seasonal storage. We much prefer our current 16x24 one story with a cath ceiling, though I have to kick the air up there around the room to mix for heating season. In summer heat we do get a good heat dump out my high peak venting outlet (6" with a 10" bell) and windows open below. That keeps the summer heat from 'stacking downward' as it did in our first summer there.
The 16x24 is about the same sq.ft. as the 12x24 c/w 12x12 loft and so much easier to use.
May I recommend you visit some of the pre-built shed places to step into the diff sizes to get a sense of the enclosed space? You could even have some cardboard 'footprints' of the big furniture, etc to toss down and move around for traffic/use flow.
You may be surprised by how much more room you get by adding 2' to your 12' wide, or 4' to make a 16'. Same on every 4' added to 12' long.
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cluelessinKY
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# Posted: 8 Oct 2023 00:11
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Thanks for your thoughts so far, everyone! ICC, I definitely hear you regarding the problems with lateral movement. All the learning is blurring together from studying so much so quickly, but I feel sure it was your warnings on other threads that got me thinking to skip the posts and tie directly to piers.
On that note, I just want to say thank you to everyone who contributes so much to this forum. It’s an unbelievable resource and I just really appreciate the time and effort you guys all give to share your knowledge with those of us trying to learn these skills! Seems to me that everyone should be taught these skills.
And yes, I also hear you all on the size of the build. My thought was to build small on this one, get our screw ups and learning in with a “cheaper†build, and build a bigger, nicer structure in the future. We spent the better part of three years in a 3 person tent and/or a car, so a 12x16 BUILDING is an improvement! : ) But still, if I can expand for not much more expense, maybe I should.
gcrank1, that’s great advice to go to the premade shed shop. We did that very early on (back before research taught us we can’t just live in a shed bc moisture issues, etc), but it has been a while. We don’t have any furniture, but I’m sure more room to spread out would be nice.
Please keep any other thoughts coming, and thank you all again for your time. Maybe I’ll get good at this and be able to share knowledge with others someday.
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gcrank1
Member
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# Posted: 8 Oct 2023 08:51 - Edited by: gcrank1
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Also use the 'tiny home' sites/blogs for ideas, especially organization and storage.
Some folks have done well starting with a prebuilt shed and insulating/modding to their purposes. Most shed builders will build to suit many of your notions, it isnt just what ya see on the lot.
Garage kits are another 'starter' build, though they typically are made to go on a foundation or slab you can put the superstructure on a pier and floor deck just as well.
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Aklogcabin
Member
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# Posted: 8 Oct 2023 10:21
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First off, congratulations on making the jump into cabin life. As stated a 12x16 is small. Maybe this is what you want. I enjoy having a loft for the bedrooms. With proper ventilation like a window or 2 I don't believe it would be an issue. Especially if you use it year round. And having the storage area is great. I can see little downside to having extra room with a loft. And it's easier to heat. Our 16x24 has a loft and we really enjoy it.
Building your support posts. Sono tube all the way to the support girder would work well. Not having a break in it is stronger.
Hey good luck n have fun. And remember that you are building a small structure. Not a complicated heavy home.
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Brettny
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# Posted: 9 Oct 2023 10:29
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I would also say to go directly from tje sono tubes to the girder. Just easier in the end. I would build the building bigger too. If you use foam board above your roof rafters and below your roofing you dont need to use spray foam and lower the cost..so you can build bigger.
Generaly any lumber yard (even the box stores) can get or carry 20' lumber. I would do 20x12' or 20x16.
Is is our 20x32' the 20' width means you need a 3rd girder and row of sono tubes. 20' 2x10 floor joists, trippled up 2x12 girder. 2x10 roof rafters and 2x6 wall studs.
Dont skimp on the foundation and I suggest you play with a interior layout program to see actualy what fits where in a 12x16 building.
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rpe
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# Posted: 9 Oct 2023 11:32
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Expansive clay is very tough on piers. To prevent damage due to uplift and frost side-loading, here's a few thoughts:
1.) Regardless of pier type, backfill all around with gravel. Don't let any clay get near that new pier!
2.) Incorporate a french drain system to allow sub-surface water to drain away from the building site.
3.) Build concrete piers with rebar right down to the footing pad. Our cabin when purchased had several concrete piers cracked through, but kept together by the rebar holding the sections in alignment.
4.) Consider tapered pier forms to prevent up-lift. See https://foottube.com/ or similar.
Good luck! It sounds like you have been quite thorough with the research!
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Brettny
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# Posted: 9 Oct 2023 11:58
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Quoting: rpe 1.) Regardless of pier type, backfill all around with gravel. Don't let any clay get near that new pier
When you do this in clay soil you make a french drain but it has no where to drain. It can actualy be worse than backfilling with clay.
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rpe
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# Posted: 9 Oct 2023 14:22
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Quoting: Brettny When you do this in clay soil you make a french drain but it has no where to drain. It can actualy be worse than backfilling with clay.
Hopefully there's some gradient to the build site that will allow point 2.) to address that issue. If not, gravel/sand is still preferred IMO as the gravel or coarse sand does not support 'micro-lensing' which is the primary mechanism of frost heave damage.
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Brettny
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# Posted: 9 Oct 2023 15:32
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With clay around it anything but more clay can hold water. Your better off useing the clay to your advantage and allowing natural run off to work. Keep all the water on the surface and use swales to keep it away from the foundation.
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ICC
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# Posted: 9 Oct 2023 17:56
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Quoting: Brettny It can actually be worse than backfilling with clay.
water flows into sand and gravel fill just as easily as it can flow out. To flow out there must be a lower place for the water to go. And clay is nasty.
Ditto on Brettny's second comment
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jdg81
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# Posted: 13 Oct 2023 09:37
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In your neck of the woods and have been considering something similiar as you. I've found the following book interesting. https://store.doverpublications.com/0486236315.html Was able to get it from my local library. Lots of these use post framing for the foundation which in my understanding is a good way to make piers a more viable and secure option.
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