View Full Version : What will give strongest floor joist?


widerberg
01-01-2011, 07:41 PM
Hi, All:

I'm building a smallish shed in the backyard. It'll be a 10 x 16 foot structure. Currently, my thinking (due to permitting, etc.) is to go with something sitting on a whole bunch of Dek-Blocks (concrete piers), and then anchored to the ground with augers. My idea is to go with 2x6s floor joists on 12" centers and 3/4" plywood on top.

My question is, what will give me the strongest floor joists...screwing the joists into the end boards directly, or using something like Simpson Strong-Tie joist hangers tying the 2x6 support boards into the end boards?

Any advice would be appreciated, but things like building a permanent foundation, pouring concrete, etc., won't work in my current circumstances.

Bo

bczygan
01-01-2011, 08:21 PM
Does it require a permit if it has a permanent concrete slab? If so, I would first remove all organic matter and topsoil, place a layer of landscape fabric and then install a compacted layer of stone or gravel. Make it a gravel that will allow water to drain through it. Make the layer higher than the surrounding grade. Build the shed floor directly on closely spaced 4x4 or 6x6 treated timbers. Spike them into the ground with 2' spikes of rebar every 4'. If you are worried about wind, then place augers and strap the walls to the timbers and the roof to the walls. This method will keep the floor closer to grade allowing a smaller step up. If you go with joists and blocks, indent the blocks into the ground and use treated joists. And the joist hanger is much much stronger, and you can also drive nails through the end of the joist as well.

Bill

D.J.
01-01-2011, 08:26 PM
What are your plans for the structure, weight of items installed inside it, etc. I would think 2" X 8" or 2" X 1" minimum. I don't know the answer to the screwing or simpson question, but I would think screwing would be strongest, but we need to let the engineers on here answer that one!

tncatadjuster
01-01-2011, 09:23 PM
I purchased four of the large parking stops. I ran these under the long side of the 12 x 16 dimension. I secured eyebolts through the stops with the eye on the top. I then built the floor on top of the parking stops out of 2X6 and 3/4" plywood. Lag bolted through the eyebolts into one of the floor joist for a total of eight attachment points. I double plated the top plate so that there would be enough room to flip a 4x8 sheet of plywood without going out the door.

I can't see the need for the strong ties. What are you going to do with the building?

tcianci
01-01-2011, 10:31 PM
The method of attachment depends on how you're going to support it...If you use supports that contact the underside of the joists, then the hangers will provide no useful function at all, they are designed to hang the joist from the rim joist or band joist where the rim and band are supported by the foundation or footings of the building. If the rim and band are indeed the members supported by the foundation or footings then the hangers are required. Clearing the topsoil and installing the landscape fabric and gravel are a good idea. In any event end nail the joists to the rim in order to get them flush with each other and then install the hangers. This is especially important if you're framing with pressure treated lumber as the moisture resulting from the treatment causes the wood to attain various widths , not only from board to board but even from one end of a board to the other. Use fasteners rated for the materials you are fasteneing.
Your plan for spacing the joists on 12 inch centers is overkill. I will assume that your plan is to let the joists span the 10 foot direction, for this, 2x6 on 16 inch centers will work fine, especially with a t&g plywood or OSB floor.

widerberg
01-02-2011, 10:47 AM
Thanks for the advice, everyone. Yeah, unfortunately, a concrete pour is out because of permitting. The gravel/crushed stone idea is interesting, but here in deepest, darkest (and wet-est) Florida, I've had treated landscaping lumber, etc., go bad in just a couple of years. Based on that, I figured treated lumber on Dek-Blocks (with no actual ground contact) would be my best bet. Although the parking stop idea is a really interesting one, too.

The joists would rest on the Dek-Block piers, either 20 or 26 of them, depending on the design, so I guess the hangers won't be all that effective. The product I'm considering going with can be seen on www.deckplans.com. It's what the local DIY/Box stores carry and I've managed to pick up 11 of the piers already off of Craigslist for pennies on the dollar. (The build's a bit of a budget project).

In terms of overkill, I'm going to try to build the proverbial brick shithouse (except out of wood, and as cheap as I possibly can). I may move up to 2x8s or 2x10s, as has been suggested. Short term, it's going to hold a riding mower and some body panels that I want cleared out of my garage, but still close at hand. Long term, there may be a chance I'll stick an old VW bug in there (which is why I'd like to overbuild the floor). The way the Dek-Blocks are positioned, a bug's wheels, if parked centered in the shed, would rest right on top of Dek-Blocks, so there "shouldn't" be much if any deflection in the floor.

I'm relatively confident the design would hold a VW, because another dubber built something similar (except without concrete piers) a few years ago: http://www.thebugshop.org/bbone.htm

claymont
01-03-2011, 03:32 PM
I built a 14'x23' two story shed on a grid of sonotube piers approximately 2'x4', 35 piers total. I then anchored 4"x4" down to the piers following long dimension and lagged 4x4 perpendicular on 2' centers to them. Screwed an glued t&g 3/4" plywood to them. Although, it's only gonna see my snowblower and a couple of rollaround toolboxes, I wouldn't be afraid to roll that VW in it as it sits. For a little added safety I'd probably roll it onto a 1-1/2x8 or so planks. What I'm trying to get across is for a "shed"... 2' centers are adequate. In my location, I looked at a lot of manufactured sheds and all of them were on 2' centers. You could get closer spacing but that was a pricey extra.

56nash
01-03-2011, 04:44 PM
I built my 10x12 on pier blocks, there are 9 of them under it with 4x4 timbers running across the top of the blocks each on a 10x10 grid. I then did a 2x8 joist running perpendicular to the 4x4 cross members. I cantilevered the last foot on each end out each side. It has been a great shed, been through 9 winters and the only complaint I have is that I was too lazy to finish with using hardware cloth in the eaves to keep the birds out and last spring we found that a family of pigeons had nested on top of our patio cushions.

bczygan
01-04-2011, 12:23 AM
Thanks for the advice, everyone. Yeah, unfortunately, a concrete pour is out because of permitting. The gravel/crushed stone idea is interesting, but here in deepest, darkest (and wet-est) Florida, I've had treated landscaping lumber, etc., go bad in just a couple of years. Based on that, I figured treated lumber on Dek-Blocks (with no actual ground contact) would be my best bet. Although the parking stop idea is a really interesting one, too.

The joists would rest on the Dek-Block piers, either 20 or 26 of them, depending on the design, so I guess the hangers won't be all that effective. The product I'm considering going with can be seen on www.deckplans.com. It's what the local DIY/Box stores carry and I've managed to pick up 11 of the piers already off of Craigslist for pennies on the dollar. (The build's a bit of a budget project).

In terms of overkill, I'm going to try to build the proverbial brick shithouse (except out of wood, and as cheap as I possibly can). I may move up to 2x8s or 2x10s, as has been suggested. Short term, it's going to hold a riding mower and some body panels that I want cleared out of my garage, but still close at hand. Long term, there may be a chance I'll stick an old VW bug in there (which is why I'd like to overbuild the floor). The way the Dek-Blocks are positioned, a bug's wheels, if parked centered in the shed, would rest right on top of Dek-Blocks, so there "shouldn't" be much if any deflection in the floor.

I'm relatively confident the design would hold a VW, because another dubber built something similar (except without concrete piers) a few years ago: http://www.thebugshop.org/bbone.htm

Based on what you said above I will modify my suggestions. Wood joists of sufficient strength will be deep, closely spaced and expensive. Your cheapest method is to prepare the ground as I suggested by removing any organic material. In Florida you have a great material for compacting and drainage. It is marl. A mixture of sand and crushed Coquina rock. It packs well and is cheap and readily available. Make a base of this and hand tamp it into place. All you've spent so far is a lot of labor for excavation and installation and small money for the material. Now place conc. pier block, solid block, regular block or concrete parking bumpers, or whatever else you can get. Place them very close together. Leave spaces no bigger than 8" between rows in both directions. Level the tops of all these concrete items to say 4" above surrounding grade. Fill around the outside of this temporary foundation with marl until above the surrounding grade. This will provide for drainage. Now, build your floor system as a grid of wolm. 2x4's on the flat running on top of these rows of conc. foundation piers. This will be cheaper than any joists. Put your floor deck right on these. The idea here is that concrete is a cheaper material and your labor is free. You've provided a great supportive base that is almost as strong as a poured slab but meeting the requirements of being temporary. In fact, if you want it to be carried to the extreme, fill in the whole space with concrete shapes and just put the wolm. plywood floor right on it. I would put visqueen between to stop moisture transfer from the concrete. Advantage is very little step up from surrounding grade, good drainage away from the wood deck, little cost for wolm. wood materials, very strong, and meets letter of the law.

red
01-04-2011, 05:43 AM
You get 25% more strength from doubling up the joist then by going 12" on center. (ie. 2-2x6 @ 16 oc is 25% stronger than 1 - 2x6 @ 12 oc) Like the parking stops idea. Screws hold things together better but with framing you are looking at shear strengths. Nailing is better in most applications for shear strengths. I like those DeckMate screws, they are twice the thickness and coated and usually less than a dollar extra per box. Not an engineer!

widerberg
01-05-2011, 10:54 AM
Bill and Red, thanks so much for the input. I think doubling up on the lumber, especially under where the wheels of a potential VW would go would definitely be a good idea, and I think I'll go with that. Bill, your breakdown is incredibly detailed, and despite cringing at the number of concrete piers I'll need ;), I think I may go with your plan. Just need to source and price out the marl locally.

Kevin54
01-07-2011, 03:36 AM
I have a 12' x 16' shed and the floor is 4x4's with treated tongue and groove flooring. Rock solid. I have picked it up with grappling hooks on the back of a wrecker and had it dragged to move it and the last time it was moved probably a total of 800' with to skidloaders and forks. It did absolutely no damage to it at all. I wouldn't be afraid to park a truck on the floor of it. The foundation it sets on is nothing more than crushed stone, mildly compacted but running over it with a roller. It's been setting there for four years now and has not settled at all