Author Topic: 20' x ~14' on a small ridge in VT  (Read 4550 times)

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Offline 802chico

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20' x ~14' on a small ridge in VT
« on: July 12, 2013, 01:30:04 PM »
Hello, I've decided to enlist the assistance of the active members on this forum for assistance with designing a strong small cabin. Its one open room, one level and with a shed style single slope roof.
I could use some help on how to leverage the foundation that is already in place. Needless to say, I'm a green horned n00b here and my only certification is a pair of big brass ones.

The piers are (6) 5'-tall precast cement piers in the ground, each has a 2' belled out foot, they are all sitting on rock. The rock was mostly shale and for some we had to pick away at hard rock to make room.

They are in 2 rows of 3 each. The long row is 20' and the short row is 8'
The distance is based on the center of the 2' footer because the top of the pier has a threaded 5/8" insert.

For better or for worse, these are in the ground and this is what I have to work with. because its on a ridge, there is no more room, so I'm hoping to get creative with the build and this is where your input will help to determine where we go from here.

I want the build to be part fire tower, part cabin and part influenced by a tree house. I will post up more sketches and thoughts on the initial build as soon as I can. For now I just wanted to toss in a post and let you know that I'm here!




Offline 802chico

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Re: 20' x ~14' on a small ridge in VT
« Reply #1 on: July 12, 2013, 01:42:05 PM »
here is Version 01, with a floor.
Still need to add some bracing to the legs and clean up some edges, just putting it up to stir some conversation and input on the direction this is heading.
I'm hoping to use Simpson Strong-Tie brackets everywhere that I can.

Floor
2.5' off the back ~5' in the front
Girder is (3) 2 X 12 x 24
Joists 2 x 12 x 16 and 8" OnCenter

beams coming up are 6x6 PT
Will definitely be looking to add more stability to the legs, so they will not remain naked as they are now.




Offline MountainDon

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Re: 20' x ~14' on a small ridge in VT
« Reply #2 on: July 12, 2013, 05:28:18 PM »
The proposed height of the posts will need real bracing, most likely more than many of us can imagine. Definitely more than a few 2x6's as many other DIY builders have used. A 20 foot long wall with some gale force winds buffeting it is going to generate some large forces. That can be bad enough with a building sitting on the ground. Note that most areas of the US should build to withstand 90 mph winds with a 3 second duration. Some areas, mostly coastal, have higher speeds to contend with.

I don't think anyone here will be able to give any better advice than to seek out a PE with a specialty in structural engineering. Note that posts fastened to those concrete piers with girders on top of the posts provides two locations where lateral movement can cause "hinging" of the post to the concrete and the post to the girder. . Lateral forces do seem to be ignored, or minimized, by many DIY designers. As the height is raised the forces magnify; think using a lever and fulcrum to move a heavy object.

Alternatively, place the girders on top of the existing concrete piers and build up from there. No posts, just the girders. Hopefully the concrete tops are at the same height.

Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline MountainDon

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Re: 20' x ~14' on a small ridge in VT
« Reply #3 on: July 12, 2013, 05:43:01 PM »
The amount of proposed cantilever is also a concern. The main side walls (20 ft lengths) will be carrying the roof loads, snow and wind,  down to the floor joists. They are overextended as far as cantilever. The amount of cantilever is covered in the IRC   http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_5_par017.htm

R502.3.3 Floor cantilevers.
Floor cantilever spans shall not exceed the nominal depth of the wood floor joist.


An engineer may design and certify something greater. Everyone else is doing some guessing and finger crossing.
« Last Edit: July 12, 2013, 10:05:43 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline 802chico

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Re: 20' x ~14' on a small ridge in VT
« Reply #4 on: July 13, 2013, 06:22:39 AM »
Excellent feedback - Thank You

I'm going to re-sketch it while bringing down the height. Was up there last night with a buddy and he also highlighted some vital details that I was overlooking.
I can tell this is going to be a ton of fun and a great learning experience.