Temporary pier and beam foundation for shed

[FordTruckWench]

I'm designing a temporary foundation for an 8x15 storage shed. The shed needs to be at a specific elevation: About 42 inches floor to ground at the downhill (long) side, and 32 inches at the uphill side.

I've decided on a floor of tongue and groove Douglas fir 2x6's laid the long way. They'll be supported by 4x6 floor joists spaced approximately every 2 feet. The ground to joist elevation is thus 25 to 35 inches.

I've been going in circles trying to find the best way to support the joists. I've considered having two 15' 4x beams each supported by four to five 4x4 posts sitting on concrete pier blocks. The posts would be diagonally braced either to the next post or to the beams. But I'm not happy with this design.

Another idea is to omit the 15' beams. A pair of posts and pier blocks would support each joist. The materials for this may actually cost less than the other design, but I'd have to align and level two rows of 9 pier blocks.

Q) Is there some other simple design to consider?

Note: Eventually the shed will get a masonry foundation. This will require that the temporary support posts do not bear around the perimeter. It would be nice if the pier and beam design can readily be modified to do this.

Q) The only pier blocks I've found locally have a square of 2x6 lumber nailed on top in a depression in the concrete. This does not seem appropriate for a wet (i.e. outdoor) area. How/where can I find a better design? Somewhere I saw piers with embedded metal straps to attach the 4x4 post.

 

[bczygan]

What is this supporting? IE, what is inside the structure?

And why so far out of the ground? Are you going to have a steep ramp to access it?

2x6's on the flat for a finish floor give you a lot of joints. Doug fir, actual 2x lumber and T&G make them stronger than standard 3/4 decking, so the 2'o.c. spacing of the joists is less of a concern. The extra wide joists also minimize the span.

The question I have is why wait for the permanent foundation? All the work, and cost of materials that can't be reused would be better spent on that.

Bill

 

[the GOAT]

How temporary?

Would a permanent column work?


https://permacolumn.com/what-are-perma-columns

 

[sands35]

Some locals let sheds under a certain sq ft side step inspections. That said, you don't want it to fall down the hill.

I would use piers much like a deck would. ~10-12" diameter, sunk down ~4' below grade. 4x4s up to level, then a couple 2x10s or 12 for cross members, then the shed on top of that.

If you want temporary, then dig a ~2x2' by 1' deep hole, fill it with paver base (crushed rock with lots of fines) and compact it. Then put concrete blocks on top of that.

A few of these on top of the "foundation":
http://www.homedepot.com/p/Unbranded-10-in-x-10-in-x-8-in-Concrete-Deck-Block-012023A/205613606

Use 4x4s as posts then have some 2x4 cross braces so it won't wobble or fall down. All pressure treated.

42" is rather high to have the base unsupported though. I would think twice about that. DIYing concrete piers isn't that expensive. Do it right the 1st time.

I'd also think about going to 8x16. The extra foot won't cost much more and it will fit dimensional lumber better. 15' means you are just cutting a foot off 16' lumber.

 

[nadogail]

Pier blocks with metal brackets sized to fit 4X4 lumber are sold in my local Home Depot store.

 

[FordTruckWench]

What is this supporting? IE, what is inside the structure?

General storage for now.

And why so far out of the ground? Are you going to have a steep ramp to access it?

I want the floor at the same level as the floor of my house. At the house it is only ~16" above the ground. The yard slopes down somewhat. Also, years ago I scraped the topsoil off of the shed site - that alone accounts for about a foot of the 32" height.

The question I have is why wait for the permanent foundation? All the work, and cost of materials that can't be reused would be better spent on that.

There are two seasons here: Rain forest, and desert. One side of the permanent foundation will require excavating fairly deep - deeper than I'm comfortable doing during the wet season. The shed has been planned for years. I need to getting moving on it. No more "waiting till summer".

4x4s up to level, then a couple 2x10s or 12 for cross members, then the shed on top of that.

The 2x10's go on top of the posts, or are they lagged onto the side? The first design I mentioned was to have a 4x beam on top of the posts. (4x lumber is easy to get around here - nobody bothers doubling up 2x's.)

If you want temporary, then dig a ~2x2' by 1' deep hole, fill it with paver base (crushed rock with lots of fines) and compact it. Then put concrete blocks on top of that.

Frost depth here is 0. I'm in a very wind sheltered area. I'm on a hill so water drains away, however the ground may be somewhat expansive with moisture. And of course earthquakes! Beneath the topsoil it seems to be loamy sand. Lots of stuff gets by with just pier blocks sitting on the surface.

A few of these on top of the "foundation":
http://www.homedepot.com/p/Unbranded-10-in-x-10-in-x-8-in-Concrete-Deck-Block-012023A/205613606

My nearest Home Despot does not have these. And the website won't even show them to me. The next HD down the road does sell them. If I claim that store as "mine", then it will show them.

I'd also think about going to 8x16. The extra foot won't cost much more and it will fit dimensional lumber better. 15' means you are just cutting a foot off 16' lumber.

That has actually been my plan - the big door at one end will be recessed by a foot. This reduces the enclosed space to the 120 sq ft limit for a shed.

 

[FordTruckWench]

Pier blocks with metal brackets sized to fit 4X4 lumber are sold in my local Home Depot store.

Do you have a URL? If I can get to the product page, I'd be able to find a store near me that carries this product.

Perhaps just specifying "your" HD would be enough to start my search.

 

[bczygan]

Still not sure why you want the same finish floor level as the house, unless you will have a deck connecting them together. It makes the shed inaccessible for larger lawn equipment and difficult to get machines or equipment into or out of it.

In any case, lets look at the other things you mentioned.

Will this have a permit pulled? I assume not, because of the 120SF limitation. You still have to build to code. Remember to check your zoning restrictions and easements.

If the aim is to hold it up temporarily, until you can put a permanent foundation under it in the summer, then you want to do the least possible for now.

What are the requirements for a permanent foundation? How deep and wide of a rat wall is required? Will you be building the wall out of block? If so, I would use those same block right now, to build a temporary support.

Here's what I would do.

Dry stack block as required to support the floor framework. Use the block that you will later reuse for the permanent foundation. How you prepare the ground is up to you and depends on the existing conditions. I would stack the block continuous, all the way around the perimeter of the shed. When you do the floor framing, you will have a band joist on the long dimensions and end joists on the short ones. The long ones, can be 4x6's, just like the joists. These members will act like sill plates/beams, and will be supported by the dry laid perimeter foundation wall.

I wouldn't worry about earthquakes if this is temporary.

Leave out two blocks in the top course on each of the long sides. Space these out. When you are ready for the permanent foundation, run a 4x6x10 or 12 through these to use for lifting points, to jack the shed up so you can dig, pour and build a permanent foundation. Leave the same 4 block out of this permanent foundation to allow space to lower the beams into. Lower the structure, remove the beams and secure it to the foundation and install the four missing block.

The only extra cost is the 2 lifting beams.

Capish?

Bill

 

[nadogail]

The Home Depot SKU # 324224

 

[FordTruckWench]

Still not sure why you want the same finish floor level as the house, unless you will have a deck connecting them together. It makes the shed inaccessible for larger lawn equipment and difficult to get machines or equipment into or out of it.

That level is also approximately the level of the garage floor and driveway. Plans are to eventually pave a parking pad / patio along the north side of the house where nothing useful grows, i.e. between the house and shed. The large elevation differences will go away. BTW, there are no lawns around here - I'm in a redwood forest.

Will this have a permit pulled? I assume not, because of the 120SF limitation.

Correct conclusion. Site limitations mean I can't do much more even with a permit.

You still have to build to code. Remember to check your zoning restrictions and easements.

Been reading code books. The pertinent requirements are staying 50 feet away from a creek and designing the permanent foundation with regards to a down slope.

Will you be building the wall out of block? If so, I would use those same block right now, to build a temporary support.

I plan to use mortarless head joint speed block:

It is useless for holding weight until all the cavities are filled with concrete. Essentially it is a concrete form that gets left in place.

Dry stack block as required to support the floor framework.

I've considered this. And rejected it. The stack needs to be too tall and of a block type I won't need later.

I may use a hybrid approach: Stacked block on the uphill side, piers and posts downhill. This'll eliminate short (10" to 12") and hard to brace posts on the one side.

Leave out two blocks in the top course on each of the long sides. [...] run a 4x6x10 or 12 through these to use for lifting points[...] Lower the structure [...] install the four missing block.

Capish?

Yup!

Location: St. Joseph, MI

I grew up there...

Location: DETROIT! Arsenal of Scrappers

...and then spent some years in Ann Arbor. But then I escaped. P.S. I forgot and left the lights on.

The Home Depot SKU # 324224

Searching that number doesn't work. I found this:

http://www.homedepot.com/p/Unbrande...ete-Pier-with-Strap-Block-100002710/100321949

But no location within 100 miles has any.