Sill For Shed

[Backyardigan]

I'm building a shed on concrete piers (the x's) spaced 6 feet apart in a 12 foot by 12 foot square as below:

x  x  x

x     x

x  x  x

I have a pile of not-too-old 2 x 4,6,8,&10 pressure-treated lumber for the sill, framing, et al.  My budget does not allows for buying 6"x6" (or whatever) pressure treated lumber.  I'm doing it with the wood I have on hand.

I would appreciate suggestions on making the sill.  The plans and advice I have seen online for sills are for a foundation that is a continuous concrete wall, and that is to put one pressure-treated 2x? flat on the foundation.

Since I just have piers every 6 feet, my thought was to craft a beam with a 2x4-1/2 piece flat on the bottom, and 2x3 pieces upright on top of it for rigidity:

123
123
123
XXX

where '1', '2', and '3' are 3" pieces ripped from a 2x6, and 'xxx' is from a 2x10 ripped in half.  I have a box of 1/4x4-1/2 lag bolts and lots of good nails.  I figured I could bolt and nail this together pretty securely. 

Would such a fabrication be overkill?  Inadequate?  Is there a better way to fabricate a sill for such a shed with the wood I have on hand?

==

Also, regarding pressure-treated lumber, when I acquired this pile of old pressure-treated lumber, I was unaware that wood-preservative products such as Cuprinol were no longer on the market.  My idea of cutting pressure-treated lumber in two was predicated on being able to seal the exposed cuts and just generally rejuvinate the wood,

As I have been unable to obtain any "real" wood preservative, I would appreciate any suggestions on how to treat this wood for resistance to rot and termites. My plan is to paint it with a mixture of linseed oil and ant/cockroach pesticide (.5% pyrethrin).  We have a lot of humidity and termites here in Maryland!

[MountainDon]

  to our forum

Answers in many parts....

Re cutting PT wood. I've purchased preservatives for coating end cuts and the like from both the Blue and the Orange big box stores as well as the old fashioned lumber yards. Different brands at different times/places. But anyplace selling PT wood should have it, generally in the paint/stain/wood finishes departments.

[MountainDon]

The plans and advice I have seen online for sills are for a foundation that is a continuous concrete wall, and that is to put one pressure-treated 2x? flat on the foundation.

That is because pier foundations may not be approved by building permit departments. So the first question is, does your building site require you to get a permit before constructing a habitable building?

I re-read the OP.... if a true shed, for storage etc, not a habitable space, there may be no local requirement for building permits. The 12 x 12 size may place a true storage shed within the local "no permit required" category. In that case it just needs to be sturdy enough to support expected loads.

[MountainDon]

If building on piers the usual method is to use beams on the piers that go down the long side, or the side where the walls support the roof. Assuming a shed type or gable type roof is used the sides under the eves carry the weight of the building. The floor joists are then placed on or hung from the beams. The floor joists than carry the weight to the beams.

Beams can be either a solid timber, like a 4x6, 4x8, 6x10, etc. Beams can also be built up using 2z lumber. The correct method for getting the maximum strength is to use the lumber on edge. For example, 2x8's on edge in two or three layers. With any and all joints placed over a pier there is no need for lag screws or bolts or large numbers of nails. The pier supports the load that is transferred via the built up beam. Only a few nails are required to keep the layers of the built up beam together.

The size of the beam is dependent on the load from the structure. How many floors, is there a loft, what is the snow load are all needed to correctly plan for the beam size. Then there is the question of the soil type. How much weight can the soil support. Is there freezing weather? Does the soil contain much clay? Is it wet or does it get saturated at times?

Q: Is this still a plan or has construction begun?

Have you givem thought to how the structure is to be connected to the concrete piers and how the piers will be braced against lateral movement?

[MountainDon]

If this is a true utility shed, building on piers maybe un-necessary. I have a 8x8 shed built on PT joists and beams that simply sits on concrete pads on the ground. Yes, it does move a slight amount when freezing weather hits, but as it is a shed it is no real bother.

[flyingvan]

http://countryplans.com/smf/index.php?topic=12247.msg158386#msg158386

  This is what I do for small outbuildings.  It works well because you build the floor frame then set it---your piers just have to roughly be in the correct place.  NOT a good choice for a home, just for small outbuildings.

[Backyardigan]

In reply to the excellent comments:
--12'x12' requires no permit here.
--The shed can go up 15 feet (peak of the roof), and I'm planning to go up every inch!
--As I'm not tall, I'm planning for the shed to have two stories.
--I put a bolt in the middle of each footing to hold down the sill
--The soil is clay when you dig about 1-1/2 feet down. I think it may be prone to shifting--haven't lived here long enough to really know. The pilings have no lateral bracing, just being bolted to the sills of the shed.
--I'm near DC, and most winters are mild. I don't think the ground freezes even a foot down, although I never measured. My foottings go about 2 feet down.
--In my time here, i've seen or known about plenty of termites in the neighborhood.  I was thinking of putting sand around the concrete footings and putting some tin flashing I may have on hand over the bottom piece of the sill.

Thanks

[Backyardigan]

... and this is in the wettest corner of the yard.  I was going to put in some French drain to keep the water away.

[alex trent]

Pests..

I would consider borate..TimBor or Boracare. Takes care of termites, most other insects you have there and fungi. Not toxic and easy to apply. The pyrethroid will not last long..good for the intilal kill so if you have bugs on it use some first.  I am notn sure what the linseed oil does, but i use it too as it helps repel moisture.

Is your site level?

If so, you can do probably do what MtnDon said and just lay the beams on the pads.  Use big pads, like 2x2 and you should be fine. Put on 6 inches  of gravel dug into the found. Or, as you said, yo you might do you can also pour a concrete block 2x2 and 2 feet deep and build on top of that.  Have it come 6 inches or so above the soil level to help with moisture control.on the beams. Cantalevering the joists will also hep protect the beams from rain.

There are plenty of ways to secure the beams to the blocks..some you can do yourself and some you can buy. I do not think it will move off the blocks without them...but I do not know for a fact.  I just built one like this and anchored two corners, diagonal to each other by putting posts in the ground to prevent any movement front to back or side to side.

You beam scheme sounds a bit odd and i am not sure i understand, but since it is two story, I believe you need more than it sounds like you are putting in.

[Backyardigan]

Thanks for all the good advice I've gotten.  My foundation is pretty sturdy. I'm about to lay down the floor..

I broke down and bought some new 3/4" PT plywood.  It's actually wet. I figured to let it sit in the sun for a week and then nail or screw it down. I've got plastic on the ground beneath the shed. If I nail the floor down now not fully cured, is it likely that regular summer humidity could cause the wood to buckle in the future?  Do the plies in plywood make it expand/contract more or less than regular wood (with the grain or cross)?

[MountainDon]

If the PT ply is wet nail it down now, using PT approved fasteners. For nails I like hot galvanized spiral shank or ring shank. I've had PT plywood and lumber so wet it splashes with the final hammer blow. The plywood will shrink some and that shrinkage should be sufficient clearance between panels as it will never be this wet again. Not unless it gets submerged in a flood and then there are plenty of other things to worry about as well. It will also curve, cup and warp more as it dries if left sitting there, as the sheets will not dry evenly. That will make it harder to align and secure, IMO.

[Backyardigan]

Makes sense; I'm sure it's not going to get any wetter than it is now. I think I read something about leaving a slight gap for expansion. Nailing it wet seems like the opposite--it will make its own gap when it dries.

I have a bucket of roofing tar.  Would there be any harm in smearing some on the bottom of the plywood, as it's exposed to the crawl space under the shed?

[MountainDon]

I did not gap the wet ply for our shed floor. After a year there was a slight gap and there's never been any issues with the gap closing.

I've used wet and splashy deck boards, both the 5/2 and regular 2x. Nailed/screwed them down wet and with zero gap. In fact I used bars to push them together. The gap is now larger than I like, but it's too much work to remove screws and move them. (Not too big a gap really, just larger than I like visually, if that makes sense.)

Tar on the bottom couldn't hurt I guess, other than maybe the smell for a while.