10 by 12 shed on concrete tube forms

Question

I am planning to build a 10 by 12 Shed on top of 4 concrete tube foundation and two 4x4 beams. Do you think 4 forms and 2 beams will be sufficient to store garden supplies, mower, and a John Deere lawn tractor?

For more details, I will be building a gable shed with rafters and ridge. 2x4x8 will be used for walls framing. If you have any resource or guides that you can direct me to will be appreciated. I am struggling with how to tackle roof the east way possible--there are countless methods but I am a newbie with the saw. Thank you!

Answer 1

I won't critique your specific design with the intent of salvaging it because I think it has major flaws. I'm not sure where you got it, but it's quite unorthodox. Some general thoughts:

• I don't consider 4x4s to be beams in the first place. Leave your piers low enough that you can use proper beam-size lumber, like a doubled 2x8. Proper size depends on final design, though. Even at ~6' spans (assuming mid-span piers) a 4x4 isn't adequate.

• Code commonly allows for cantilevers of about 1.5x the joist height. You're way beyond that here and risk tipping your shed with your tractor or other load (accumulated junk) imbalance. The beams should be at the wall line.

• The main problem is that you're carrying the entire structure, roof and all, on that large cantilever. That's not a good idea. Both the side walls and the end walls which will presumably carry the ridge beam rest over big air. It may seem fine initially, but it will sag over time, if it doesn't fail altogether.

I've built two sheds of exactly that size and owned them for the last 22 years (consecutively). My strategy is simply a treated lumber floor laid on crushed rock. See my related answer. If you'd rather have it off the ground, take manassehkatz's advice and use either six piers or four at the corners with proper beams.

See also Is a ridge beam necessary for a small shed roof? and my answer showing rafter design for insight into the roof.

Answer 2

I would be extremely skeptical about using only 4 concrete piers to support a 10' x 12' shed. This web page about shed foundation piers recommends 6 - one in each corner, one in the middle of each 12' side. You may even want more than that, but 6 is a reasonable starting point.

You then run a 10' 4"x4" beam across each pair of piers, and build the shed on top of that. You don't want much overhang - of the 4x4s past the piers or of the shed past the 4x4s.

I also suggest checking with your local building permit office. In many places a shed less than a certain size and not attached to another building will be exempt from many building code rules and possibly even exempt from any building permit requirement at all. However, that varies a lot by jurisdiction and you really don't want to spend many hours building a shed only to find out that you have to add more piers to satisfy local code after you have already built the entire shed. I saw one video showing how to build a shed in some part of Canada where the local rule was very strict with respect to size - i.e., reportedly just a few inches over the maximum no-permit size and the local jurisdiction could make you tear it down.