I am planning to build a 10ftX12ft backyard shed in SF Bay. We have little rain
year round except spring and fall. The shed will be use to store boxes of books,
unused items on built in shelving and should be considered very heavy.
I need suggestion, advice or webpage's links for the required foundation. I am
not in a position of laying a concrete slab as it would be too troublesome to
mix or cart in pour concrete mixed from the front yard to the backyard. Thanks a
The slab would be my first choice. A 4" slab for a 10x12 shed would be
about 1-1/2 yards of concrete. Assuming you carted about 4cu/ft in a 6cu/ft
wheelbarrow, that's only 10-12 wheelbarrow loads. Although, in SF, your
yard may be rather steep for pushing a wheelbarrow? :)
You could install a gravel bed, level a couple of pressure treated 6x6
timbers, then build a wood floor on top of those.
Or, you could build the floor like a deck with post pier blocks, beams and
joists with hangers.
My first preference would be a slab, but considering pushing or pulling a 5 or 6
cu/ft of mixed concrete up the miserable steep driveway just turns me off.
Yesterday, I tried and failed to push three (50lbs bags) concrete mix on a 6
cu/ft wheelbarrow up the driveway. I just cannot do it and ended up hauling one
bag at a time(I am not young, big and strong:-) Further, 10 or 15 loads hauling
it up the driveway and carefully maneuver into the narrow side of the house to
the back yard may cause me to meet my MAKER prematurely ....:-)
I am afraid the treated timbers may sink on one side in time, as I cannot assure
that the weight will be distribute evenly inside the shed.
I am more likely using post pier blocks, with poured concrete one at a time,
thereby allowing me to do it at my own pace. Any Internet sites that I can find
more information as to the sizes and depth?
You bet! Better ask questions and get all the information before I proceed.
Check the yellow pages for a concrete pump service.
It is about $100 in Florida but well worth the money.
When you form your slab make a ring around the perimeter about a foot
deep for about a foot into the pour, then continue at the normal 4" in
the middle. You should put a ring (or two) of rebar around this edge
in the center of the 1 foot footer (block it up with pieces of
rock/brick etc or wire "chairs") Then you will have a solid foundation
to build on. Put galvanized "J" bolts in the wet mud and you will have
something to anchor your shed to.
That is how you build in Florida anyway. Sheds here have to meet the
same wind code as a house. I am betting your earthquake code is
I visited San Francisco a few years ago, so I kind of figured that would
be a consideration. :)
You could look into a concrete pumping service as another poster
mentioned. But last time I looked into that it was over $400! So, I
suppose it varies by area.
You might check with a tool rental place to see if they rent some kind of
powered wheelbarrow or dump cart. Have the concrete truck fill the cart,
then drive it up the hill and dump it. Just another option.
If you lay the timbers on their side, they should distribute the loads
evenly. At least as well as a traditional foundation. You could lay down
three or four timbers to further distribute the weight. But, you should
have gravel under the timbers for drainage, and then you're back to how
you get the gravel up the hill... :)
The pier blocks will be point loads, so uneven settling will be more of a
concern than a timber or slab foundation. But if you install a lot of
piers it should distribute the weight better.
I don't have any links at the moment, but any deck building book should
tell you all you need to know. Check the book section of your local home
As to frost depth, that's probably not a concern in SF. I'm north of you
in southwest Washington state and our frost depth is only about a foot.
Although, if you build your shed on a slab it can just "float" with any
ground movements, so you could get by with a simple 4" slab.
You could call your local building department, or check their web site to
see what your local requirements are.
Here, where we get below well below freezing temperatures it's best to
dig post holes at least 24 to 30 inches deep.
That depth may be unnecessary your area? We prefer an open air space
under each shed (we presently have two) for ventilation and to reduce
rot. For posts we have used the stubs of old telephone poles, metal
pipes set into concrete (below ground. Others dig holes and fill a
concrete tube with cement; you can put a metal bracket into the cement
to 'fasten down' the shed structure if you ever get high winds.
Some try building on those concrete blocks, laid on the surface of the
ground but with our frost and temperatures they usually heave unevenly
and the shed or deck etc. leans. However in your area you might get
away with a treated wood deck on the ground. But wood eating
We often build our own (Total of four, including a summer cabin in our
case) or buy a partially pre-cut kit from one of the larger building
suppliers. Also depends how fancy you want it. If just for storage
shelves, spare tyres etc. Or if a place to retreat and wile away an
afternoon reading Proust with a cool drink standing by in a small
fridge, is another matter!
For you. A plastic shed? Something fireproof (metal) if threat of
Us? Well ever hear of 'The shed culture'. One's 'shed' being anything
from something you built yourself out of scrap to an old barn, to our
whole semi-urban, semi-finished 35 by 48 foot basement which is 90%
workshop and junk storage!
Get 'local' advice.
You do not want to store books outside in a shed, unless you want them
to become moldy or eaten by larva.
A shed does not need a foundation, like a house. Both my 20 year old 12
x 16 foot sheds sit on a bed of gravel, to keep the PT lumber off the
ground and air circulation.
One shed is actually a pool house with full electric outlets, and a
kitchen cabinet mounted sink running hot and cold water with a drainpipe
to the septic tank. I'm in NY so I have to drain the pipes in the winter.
I have both building and electrical COs for both sheds.
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