I am building a guest cabin at my beach house and need help determining the size for the footing, sonotubes and beams that will be the foundation.
It was easy enough to find span tables to size joists and rafters, but I couldn’t find a good source for sizing foundation elements.
Some specifics: The bulding will be 16×16, single story, and not contain and bath or kitchen facilities. Essentially, it will be an overflow bunk room. I plan on placing 9 foundation piers, running beams of built-up 2x material over them, and then running the floor joists over top of these. So maximum span for the beams will be 8 feet. If it matters, I am building in an area where codes call for 50 psf roof snow load.
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It was easy enough to find span tables to size joists and rafters, but I couldn't find a good source for sizing foundation elements
That is dependent on your soil baring capacity. Without knowing your location everything is a WAG.
Dave
guest cabin at my beach house . . . couldn't find a good source for sizing foundation elements.
The only good source would be a local soils engineer.
Where are planning on building?
Can you estimate the weight of the structure?
The worst soils to build on are clay and I believe even at that a one foot square pad footer is good for two tons. It might have been only one ton. I can't beleive a 16 x 16 shed can weight that much.
Go for overkill, 2 foot by 2 foot footers on eight pads. I would forget teh middle peir as you can easily span 16 feet without the center pier or atleast ignore it for load calcualtions as teh load will be on the outside six piers.
SO six piers at 4 square feet. 24 sq ft for load. At 1 ton per foot, will your shed weight 24 tons? I doubt it.
All a swag! So don't anyone have one of those hissy fits. Just a swag to start teh discussion and a couple of ways to look at it. Go verify my 1 or 2 ton for worst soil types and figure the weight of the structure and you are there.
I'm not going to find a soils engineer. It is going to be far easier to just oversize things a bit than get someone out to the bulding site (it is on an island in Lake Superior).The building is probably 7000 lbs. I figured 2.75lbs per board foot for dimesional lumber, 50lbs for 1/2 sheet goods and 75 lbs for the 3/4, plus the roofing. On top of this is 13,000 lbs snow load, plus whatever the contents of the building is. I never would have guessed 7k lbs, but when you add it up, that's what it is. The soil is essentially pure sand. I can easily overkill the pier size - what I'm most concerned about is the sizing of the beams that will hold the joists and exterior wall loads?Thanks
Piers in sand depend on friction to bear loads. The top 10' or so of depth doesn't count, 'cuz that part of the mass will shift during high water.
7square inches of 3500# concrete will hold 20,000#. You can oversize your piers all you want, they'll still sink if they're not long enough.SamT