Questions on Wood Shed Build

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jeffesonm

Minister of Fire
May 29, 2012
862
central NJ
It's about time I built myself a wood shed to keep the supply dry and also consolidate some of the 15+ piles scattered across the backyard. I would like to keep this simple, basically just posts and a roof. It's out in the woods so not too concerned with aesthetics, and would prefer it blends in with the surroundings as much as possible.

Just scored some used pressure treated lumber off craigslist for free... bunch of 4x4 and 4x6 posts and some 2x10s in various lengths from 8-16'. I also have at my disposal a few old utility poles in 10-12' lengths and a few ~6" diameter straight sections of trees from around the property also in 10-12' lengths.

For the roof I have a was planning OSB or plywood covered by epdm rubber. For the floor I was thinking I'd lay down epdm as a moisture barrier, maybe an inch or two of gravel and then pallets.

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I made a mockup of a 6' wide shed that's 6.5' in the back and 8' in the front, just to see how it would look from my house. I cut my wood to 16", so 6' wide would allow four rows deep with a little wiggle room. I worry too much deeper and the inside part might get punky. I know the popular approach is to season outside and move only dry wood into the shed, but not keen on moving it twice. Hoping a shallow shed with open sides and 3 years of seasoning will be sufficient. Obviously bigger is better, so thinking something like 30' or 36' long depending on post/span arrangement.

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So onto the questions...

1. How far can I span between posts with doubled up 2x10s as headers? We get some snow here in NJ, but nothing crazy. I looked at some span tables but wasn't clear which ones I should be using for this roof design/load.

2. What about footings vs on grade... in central NJ so frost line is ~42", but do I care about frost heave? No biggie if this moves a little bit and I'd really rather avoid pouring concrete. Maybe somehow tie pallets to the posts to help anchor it down against the wind?

3. Thoughts on shed depth from those who have used theirs for a while?

4. Thoughts on the flooring arrangement? Figured epdm to keep the moisture from coming up, few inches of gravel to drain any surface water and then hopefully the pallets should last a bit longer. Maybe set them on PT 4x4s if I have some leftover.

5. The ground slopes about 1' every 10' down the long side. I could excavate (no thank you) or have one side taller than the other, or just have the roof follow the contour of the ground (and still slope back to shed rain). Thoughts?
 
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shoot-straight

Minister of Fire
Jan 5, 2012
742
Kennedyville, MD
I am not a contractor on engineer. But my shed has 4*4 posts with 2*10 headers and 2*6 rafters . posts are set 8 ft apart and deep making 4 8*8*8 cells. My posts aren't deep. Maybe 24 in with a bag of quickcrete in each. Its holding up fine. Covered w metal.
 

GENECOP

Minister of Fire
Jan 31, 2014
734
Ny
Don't over think it....your double 2x10 can go 10-12' span....forget the footings, post hole digg, sink them posts into the ground 16"....Pallets on the grade will last a couple of seasons....more permanent would be some basic ACQ framing with decking....My storage shed is 4' deep...
 

Poindexter

Minister of Fire
Jun 28, 2014
2,436
Fairbanks, Alaska
If you can get a 4-6" air gap between each layer of wood it will probably sesaon just fine in three years. The high rollers with real estate up here put 8" air gaps between layers of 16" splits and are ready to burn after one summer.

Dunno about the structural engineering side, I know just enough to ask what your expected snow load is, but not what to do with the answer to that question,
 

jaoneill

Feeling the Heat
FWIW, It is highly unlikely that those 4x4's are rated for ground contact (.60), most that are sold are only .40 and there is only a 50/50 chance that the 4x6's are .60. The .40 will only last 6-8 years in the ground. Hard to tell from the pic but it appears that some of your 4x4's were already crapping out at ground level in their previous location. Cut yourself some locust posts, peel the bark off and they will last close to a lifetime. We pulled some locust fence posts last year that we put in the ground in 1962 and they were as hard as the day we put them in. Whatever you do, never, never, never pour concrete around a wood post; it traps moisture against the wood, greatly accelerating decay. Ideally you should backfill with coarse sand, gravel, or washed stone.
If you put down a vapor barrier there are much less expensive choices than EPDM; 6mil poly is perfectly adequate as long as you put a few inches of stone over it (use washed stone, it's cheaper than crushed stone and the crushed will tear the poly). Without pulling out my span tables I would agree with genecop that 10'-12', even 14' is an acceptable span for the dble 2x10's. Your snow load is probably in the 40lb range and the rafter span will only be 6' (which means that only 3' of the weight of the rafters is bearing on each girder).

Good luck,
Jim
 

jeffesonm

Minister of Fire
May 29, 2012
862
central NJ
Thanks for the feedback all. Three 12' bays x 6' deep stacked 6' high would hold 10 cords, which sounds good to me. I will probably just use the utility poles and trees as posts and either bury them slightly or set them on concrete slabs. I realize the flooring is a bit overkill but I have a whole bunch of used EPDM I got from a leftover roofing job so might as well use it.
 

clr8ter

Feeling the Heat
Oct 4, 2010
261
Southern NH
My shed structure is built almost entirely from 4x4's. I spanned about 10 or 12 feet with just one, and it's holding up fine. I did go for new PT ones for the corners, but all the ones off the ground are just plain fir. (They were free) My shed just sits on some aluminum brackets I made, technically NO ground contact. Inside, there is no floor at all. I got some large skids, cut them to fit the shed, and put them up on plain old bricks, one high. There is occasionally some water in the area, but it's never been a problem.
I also HATE moving wood more than once, but I would be real reluctant to season in the shed. Even if it would season with small spas between, I'd consider that a waste of valuable space. Burning 4 cords a year would force me to build a lot of roof to cover everything, with the nice big air gaps that I like.
 

jeffesonm

Minister of Fire
May 29, 2012
862
central NJ
Do you think I need to go 16" OC for the 2x4 rafters? Or can I get by with 24" OC? I was planning OSB over the rafters and then glue the EPDM to that.
 

clr8ter

Feeling the Heat
Oct 4, 2010
261
Southern NH
What's the span of the 2x4? At an 8' span, I would only use 2x4's if you get NO snow. For an 8' span, I'd feel comfortable going 24" with 2x6's. Now, the bigger problem is the OSB. Under snow load, asking OSB to span 24" is possibly too much. If it gets wet AT ALL, forget it. My shed has 4x4's spanned about 7', spaced 24' OC, with 1/2' OSB on it. The structure is fine, the OSB is sagging. (I should have known better, but I was on an extreme budget) Next time, I would go to plywood, thicker OSB, or less spacing.

I would also not glue down that EPDM rubber. If you ever have to replace that OSB, kiss the rubber goodbye. There are other ways to attach it, and since you're not building a house, it'll most likely be OK.
 

jeffesonm

Minister of Fire
May 29, 2012
862
central NJ
I have modified the design slightly to be 8' wide instead of 6' wide. I also scored a bunch of 7/16 OSB free off craigslist. Can I span 8' with 2x4s 16" oc? I could do 2x6 24oc but worry the OSB would sag, and 2x6 16oc seems crazy for a shed roof.
 

jaoneill

Feeling the Heat
With an 8' span you might want to use 10' rafters to have a bit of an overhang.

The OSB will unquestionably sag at 24"oc; it will sag some even at 16"oc. If it was me I would use 2x4's @ 12"oc, it will only take a half dozen more 2x4's for a 30' long shed and at 12"oc they would be more than adequate structurally, as well as solving the OSB sagging issue.

Jim
 

clr8ter

Feeling the Heat
Oct 4, 2010
261
Southern NH
I'd have no issue with 2x4s spanning 8 feet @ 16" OC. The snow load in NJ is probably less than here in NH. The OBS SHOULD (maybe) be ok, too. What kind of roofing is going to be on top? A quick, cheap solution would be to add a couple of 2x4s, and reduce the spacing. Really, another $20 for some more wood is cheap insurance against having to tear it all apart in a few years.

Also important is to make sure the roofing is going to be watertight. If it leaks, that OSB will come apart real quick. A tarp WILL NOT do the job, even on a wood shed.
 

jeffesonm

Minister of Fire
May 29, 2012
862
central NJ
2x4s 12" OC sounds reasonable.

For the roofing I have some sections of EPDM I plan to put on top of the OSB. I need to lay them out and see how few pieces I can get away with. Anyone have suggestions on how to join pieces together? A bit of searching and it sounds like they make either a tape or a primer/cement, but neither one are cheap.
 

clr8ter

Feeling the Heat
Oct 4, 2010
261
Southern NH
It'd be nice to get it all in one piece. If that wasn't possible, I'd start from the bottom. Secure top and bottom. On the next piece up, take the rubber and lay it over the first piece. A couple inches down the first piece, put a thin, narrow board on top of both. screw down thru the board and both pieces of rubber. Now, fold the second piece up, over the wood and secure the top. Continue. Use as thin a wood piece as possible, since it will make a bump in the surface to catch leaves, sticks and other junk. If it was shaped like a wedge, with the sharp side uphill, that'd be nice. If you have to join it side to side, I don't know about that one...
 

jaoneill

Feeling the Heat
Best to spend the $ and get the primer/cement. Rubber has to be CLEAN where you are joining it, temps should be well above 50 degrees; don't skimp on the primer or cement. no need for the seam tape, just overlap the joints 4-6 inches (horizontals as well as verticals).

DO NOT use regular roofing (tar) cement. We recently did a $2,000 repair on the roof of a local business whose maintenance man used "bear chit" to try to solve a leak on their EPDM roof; what a mess it made.....
 

clr8ter

Feeling the Heat
Oct 4, 2010
261
Southern NH
Ughh. That "tar in a can" is the most useless crap ever made. Good for nothing, and no good.
 
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