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jdevoe
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# Posted: 17 Jul 2008 13:45
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I will build a 16x16' cabin near the ocean in Maine this coming August. A local who I was hoping to have set some posts for me before my arrival quoted $3k. After getting back into my seat, I am now setting off to do this myself too (with teenage sons). I need to know if 4 6x6 pt corner posts are adequate to support the load or if I need a 5th (middle) post or 6 or 8? Any advice based on experience welcomed. Dream on.
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CabinBuilder
Admin
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# Posted: 17 Jul 2008 14:38 - Edited by: CabinBuilder
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I think 16' span between posts is too much - I would add AT LEAST 5 more posts to support the cabin - in the middle of each wall and one in the middle of the cabin.
That would be 9 posts total, with 8' span between posts.
The floor frame would need to be strong as well, with side and middle beams doubled (two 2"x10"x16' nailed together).
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jdevoe
Member
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# Posted: 18 Jul 2008 14:50
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I was afraid this was the advice I would receive. Any practical tips on setting up the perfect, level square with 9 posts on uneven over grown field? I was shocked at how difficult it was to stake the perimeter the other day.
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CabinBuilder
Admin
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# Posted: 18 Jul 2008 16:07 - Edited by: CabinBuilder
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Mark post locations on the ground, dig holes and set the posts - they will have uneven height (I assume that's your worry).
Then use a string with a level attached to it, to mark and then cut ports according to the level.
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soundandfurycabin
Member
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# Posted: 18 Jul 2008 18:39
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Sounds like a great family project you have planned.
For such a small place, nail four straight 16' pieces of lumber together, square them up (measure the diagonals) and brace the corners. Then support and level using scrap lumber in between where the posts will go. Use clamps to hold the supports in place while you adjust things reasonably level, then screw or nail in place. Use this temporary frame to locate the post positions. You can drag it out of the way when digging the holes. Then move it back into position and use it to support the posts while you backfill or pour concrete around them. As Cabinbuilder said, leave the posts a bit long and cut them to length after they are set. A water level is a good tool to use for this.
I'd think 6 posts would be the minimum... a beam at each side supported by 3 posts each. 2x12 floor joists will span the 16' (actually less, due to the width of the beams). You could get by with 2x10 joists spaced 12" apart if you moved the beams closer together (say 14' apart, letting the floor overhang by a foot on each side). Or you could use the 14' beam spacing with select structural grade 2x10's spaced 16" apart.
If you have bad soil (lots of clay, prone to settling or frost heave), then you might go to 4 posts on each beam. But I'd avoid the middle beam with a post under the center of the cabin. If the posts are all around the outside edge, it's easier to jack up and relevel the cabin if there was any settling.
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jdevoe
Member
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# Posted: 22 Jul 2008 13:40
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Thanks folks. I was actually more concerned about the square, than the level, which I envisioned exactly as Cabinbuilder recommended. I appreciate your advice soundandfury and had actually came to the same conclusion using way too much brain power. Having fun sketching and engineering despite lack of experience. The ground is very uneven and of unknown dirt/rock/root composition. I think that I'll rent a power post hole digger, or just whip my kids harder, to dig the post holes atleast 48" as Maine has a killer frost line. We may hit granite before then. Cheersl
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jdevoe
Member
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# Posted: 22 Jul 2008 14:04
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Soundandfurycabin or cabin builder, are you setting the cabin on top of the posts or attaching the 2x10s to the posts on the outside for form the box within which the floor joists will be hung? If the former, how to attach the beams to the tops of the posts? Toenails only? or some form of bracket?.
My initial plan was to actually lag bolt them to the posts around the perimeter. Maybe with settling, etc, not a good idea? Still formulating the plan but this is the most important part. Cheers.
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CabinBuilder
Admin
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# Posted: 23 Jul 2008 10:33 - Edited by: CabinBuilder
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I also when through this when designing my cabin.
You should set up floor frame on top of posts rather than attaching to post sides. It is much stronger option.
You could use metal brackets to keep cabin posts and floor frame together.
Something like this:
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soundandfurycabin
Member
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# Posted: 24 Jul 2008 22:48
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I agree, resting the beams on top of the posts is stronger as well as easier to do. And being near the ocean, you won't have to worry about the bolts corroding over the years. Resting the joists on top of the beam instead of hanging them is a good idea for the same reasons. But hanging them is fine too, especially if you want to keep the cabin lower to the ground, as Cabinbuilder points out somewhere on the site.
Instead of the metal bracket, you can just support the beam with a 2x6 nailed along each side of the post and beam. If you do ever have to use bolts somewhere, keep in mind that through-bolts (with a nut on the other end) are stronger than lags of the same diameter, and unlike lags, they're never going to pull out.
For frost heave to happen, there has to be both cold temps and moisture in the soil. If your soil turns out to be sandy and well-drained, you're not going to get frost heave even with a shallow foundation.
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CabinBuilder
Admin
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# Posted: 25 Jul 2008 09:10 - Edited by: CabinBuilder
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jdevoe,
I assume your cabin will be on posts from pressure-treated timber, cedar (which contains some natural anti-decay resins), or you will pre-treat posts using some other way. Plain timber posts will rot in the ground in just few years.
For my veranda, I used cedar posts (felt sorry for cutting down those nice trees), and additionally treated part that goes below and ~1 ft above the ground with an anti-decay wood treating solution ("green stuff"). In old days people would use tar for that.
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jdevoe
Member
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# Posted: 26 Aug 2008 21:02
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See photos and thank you on Member's Projects and Photos. Thanks for all. I'll report back if it falls in.....
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Geronimo
Member
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# Posted: 15 Sep 2008 02:27
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Use rubber tubing with water in it. It can go over any sort of ground and remains level.
To get your posts in the right place, measure across to get them square. Look at a deck building book, because that's sort of what your doing.
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larry
Member
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# Posted: 22 Feb 2010 23:05
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you can rent a laser level, mount it to one post and mark the others with a square. very easy to see the laser at dusk but the level will be perfect. then cut off the tops. use 6x6 8' apart. i just did this on very uneven ground with 12 x 32 cabin.
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