making 20ft beams for shed floor...how would you do it?

[mike93lx]

planning on a 12x20 shed, hopefully next year. it will be used as a workshop for mostly woodworking.

floor will likely be 2x8, 16" OC, either sitting on three 4x6 skids, on top of 3/4" stone, or the floor will directly be on the stone.

If I can't find 20' 2x8's, should I double the rim joists? If so, is there a preferred combo of lengths (thinking either 12' & 8' or 16' and 4')? They'll be fully supported, so I wasn't concerned about having the seam in the middle 3rd like on a deck beam.

another option, which may be much simpler, would be to just use 2x10x20 for the rims and 2x8 for the joists, since 2x10x20 seem to be much more common.

or just keep it simple and join two shorter boards where needed? it's just a shed, but I'm looking to get it built properly as I'll use it as a shop for hopefully a long time.

 

[69gp]

Depending on the roof line orientation you could just make small trusses.

 

[cvairwerks]

Going to be running any heavy machines? ie cabinet saws, joiners or ??? Joist size and span limits come into play real quick when you add machines in.

 

[matt_i]

I would investigate LVLs, they are superior to "machined solid lumber" in every way especially in twist and straight-ness.

Keep them covered from weather (extend siding below) and you should be all set.

 

[pattenp]

Whatever you do, make sure the wood that sits on the gravel/ground is rated for ground contact. Treated framing lumber such as 2X8's or 2X10's are not always rated for ground contact.

 

[MFolks]

Yes,Termites and other wood loving insects will quickly ruin your constructions.

 

[mike93lx]

Depending on the roof line orientation you could just make small trusses.

for the floor? how so?

Going to be running any heavy machines? ie cabinet saws, joiners or ??? Joist size and span limits come into play real quick when you add machines in.

nothing really big. i expect to keep my jobsite-style table saw and might get a jointer that won't be bigger than 8". I'm not concerned.

I would investigate LVLs, they are superior to "machined solid lumber" in every way especially in twist and straight-ness.

Keep them covered from weather (extend siding below) and you should be all set.

PT PSL's are pretty darn expensive. Even protected from water, I wouldn't want untreated wood near the ground. I could termite-treat regular LVL's, but i expect going with engineered lumber will add significant cost for little benefit. This isn't a big building.

Whatever you do, make sure the wood that sits on the gravel/ground is rated for ground contact. Treated framing lumber such as 2X8's or 2X10's are not always rated for ground contact.

yes, ground-contact is the plan

Yes,Termites and other wood loving insects will quickly ruin your constructions.

I might spray any non-treated lumber, thanks.

 

[KenC]

I'd just keep looking 'til I found 20' lumber. In our area 2x6 is commonly available in long lengths as rafter material. That size on 12" centers would be a great floor solution I think.

Reduced flooring span, makes ply less bouncy. I'd treat the ground for insects, cover with plastic, then some stone as well as elevate on concrete pier blocks commonly used for decks.

 

[Dustball]

2x8x20's isn't too bad to find. The hard part is finding straight ones.

 

[u2slow]

Reminds me of the 16x20' deck I built a few years ago. I went with 20' 2x8's and 3 beams to hold it up. Its really solid.

With good blocking and bracing (even temporary) you can force long 2x8's straight. Almost better when they start out a bit wet, and let them dry in place.

 

[theoldwizard1]

2x8x20's isn't too bad to find. The hard part is finding straight ones.

Concur !

I would do FOUR 6x6 PT skids (triple up 2x6 pt lumber) on gravel. You need it to be far enough off the ground that light and ait pass underneath. If not varmints will make their home under it. You only want about 1' foot of those 2x8 joists hanging off the outside edge of the skid.

16" O.C. with 3/4" tongue-and-groove subfloor should be adequate. Stagger the seams of the flooring. Spend the extra money and install 2x8 cross supports every 4' between the joists.

If you are going to store and very heavy items inside, you might have to go with 2x10 floor joists.

 

[Ray-CA]

...planning on a 12x20 shed,...

Can you run the floor joists on the 12-foot dimension? That would seem to work for me.

Ray

 

[Copymutt]

Can you run the floor joists on the 12-foot dimension? That would seem to work for me.

Ray

That would be my default also. Double up on rim joists and stagger the lap.

 

[mike93lx]

Can you run the floor joists on the 12-foot dimension? That would seem to work for me.

Ray

That's the plan

 

[mike93lx]

Concur !

I would do FOUR 6x6 PT skids (triple up 2x6 pt lumber) on gravel. You need it to be far enough off the ground that light and ait pass underneath. If not varmints will make their home under it. You only want about 1' foot of those 2x8 joists hanging off the outside edge of the skid.

16" O.C. with 3/4" tongue-and-groove subfloor should be adequate. Stagger the seams of the flooring. Spend the extra money and install 2x8 cross supports every 4' between the joists.

If you are going to store and very heavy items inside, you might have to go with 2x10 floor joists.

There won't be any overhang at all. Using three, I am at a 6' span for a 2x8. My house isn't even built that well.

3/4 is unnecessary. 5/8 osb is already more than enough for 16oc. I am actually thinking of a layer of 1/2 PT ply, 1-2" of foam board, then either 1/2 or 5/8 on top. Probably 1/2

 

[brownsmustang]

I rebuilt the floor in a 12x20 shed a few years ago, Lowes ordered the 20 footers without hesitation.

 

[mike93lx]

I rebuilt the floor in a 12x20 shed a few years ago, Lowes ordered the 20 footers without hesitation.

Thanks. I'm going to call my local yard sometime soon to check on pricing. Tempted to run 2x10 on the rim, install a 2" ledger and place 2x8x12 on top for the joists. With pressure blocks between, it would eliminate the need for hangers and would be cheaper and faster to install

 

[BD1]

Have you considered concrete Piers ?
Make holes, mix concrete, and set floor framing on top.


Sent from my iPhone using Tapatalk

 

[Ray-CA]

That's the plan

Right, so maybe I'm just not seeing it.

Buy 12 foot 2x? material and run the joists across the 12ft space instead of trying to span 20ft.

Ray

 

[southalabama]

I’m not an engineer but I would use 6x6 treated skids as stated earlier.

I also don’t like bounce in my floor. I’d go 12” on center. It wouldn’t add much cost wise.

 

[mike93lx]

I’m not an engineer but I would use 6x6 treated skids as stated earlier.

I also don’t like bounce in my floor. I’d go 12” on center. It wouldn’t add much cost wise.

There won't be any bouncr anyway. Not sure where those comments are coming from.

My house is 2x10, 16OC on a 13' span. No bounce, zero tile cracking.

2x8, 16oc, 6' span will be rock solid.

 

[mike93lx]

Right, so maybe I'm just not seeing it.

Buy 12 foot 2x? material and run the joists across the 12ft space instead of trying to span 20ft.

Ray

It still requires a 20' rim board on the long edge. Need something to hold those 12' joists in place and support the walls...

 

[mike93lx]

Have you considered concrete Piers ?
Make holes, mix concrete, and set floor framing on top.


Sent from my iPhone using Tapatalk

Yeah. Don't really want to do concrete. The beam size would go up a lot, unless I do a ton of piers, raising the structure even more. It will already be elevated from the house and with an 8' side wall, it will look odd if i added a foot+ for the piers and beams

 

[ItsNemo]

I don't get why anyone would ever use wood in contact with the ground, the skid style foundation doesn't make sense.

Either pour a concrete pad or use deck blocks to lift it up off the ground. With deck blocks you can just space them closer together and take span problems out of the equation. Heck, you could just **** up two 10' boards in a block with a little scab to keep them together.

 

[mike93lx]

I don't get why anyone would ever use wood in contact with the ground, the skid style foundation doesn't make sense.

Either pour a concrete pad or use deck blocks to lift it up off the ground. With deck blocks you can just space them closer together and take span problems out of the equation. Heck, you could just **** up two 10' boards in a block with a little scab to keep them together.

Because pt does fine in contact with crushed stone. Plus a pad is way more involved and won't work in my location. The number of deck blocks I would need to replace three simple 4x6 skids would be excessivr

 

[Kevin54]

I have a 12'x16' shed, all wood, and the floor joist are made out of 4x4's treated. The shed has been moved maybe 5 times since I've lived here. It's been pulled with a wrecker and grappling hooks, moved with skid steers, and hoisted up onto a flatbed and moved. It has cedar siding and no sub siding. Never cracked a piece of siding in all those years and moving it. What ties it together though is treated tongue and groove flooring @ 3/4" thick.

 

[DFB]

Most of it is all dependent on the soil/sod or whatever you are building on

I built a shed a little smaller 8x12 square footage fell under no permit

It has a PT wood foundation just like the OP proposes...2x joisting material on skid material leveled to the ground. Its been there since like 1989 hasn't moved hasn't rotted away. I did set some large stone under the skids as I leveled the subfloor when I framed it. I did double up the end joists IIRC and stagger blocked the floor joists at the center point all the way thru. A solid soil base is needed mine was on silty/sand hardpan and good drainage is absolutely necessary mine I also graded the soil slightly away from the building just like you would do with any house and created some stone curtain drain paths to help. Massachusetts? Using crushed stone gravel as base do the job just fine IMO.

On the other hand I see a lot of prebuilt sheds delivered set on concrete block piers pretty much on sodded soil no prepared gravel bed all they do is move... sink and shift

Double up on those long rim joists after you frame across the 12 footers staggering the joints to support the 2 pc break would be what I would do. Screw finding one piece 20's Make that sub frame as solid as can be. Double the ends joists/ add center bridging too. It won't move. Adding 6 or 8 extra pieces of framing material shouldn't break the job budget. And once you subfloor it will be solid.

You haven't mentioned what your doing for subfloor material YET so lets discuss that also

Just make sure you get ground contact PT (and the right coated fasteners that should go without saying) as a lot of lumber available in box stores isn't any more.

My biggest problem after all these years was that a big fat old woodchuck tunneled under it...dam rodent

But he's gone now and the tunnels are filled with stones

Wish now I had buried some screening around the perimeter

 

[ard]

TJIs or wood ibeams come in 70 footers, as I recall. At least when Ive bought them, they cut from a 70ft long 'unit' or package.

You will get a nice true floor. Go to 12". Figure out how to control moisture under the structure. It will be a superior shop floor. IMO.

You could pour 3 stem walls, both ends at one at 10'. (Or the other way.) Just form it up 12 inches, lay PT on that. Then the joists cross wise. A concrete buggy or two.

But honestly for a shop Id just pour a slab... unless the entire floor is rot resistant, you need to be careful of moisture w low ground clearance structures

 

[Skiff Builder]

Mike,
Like the idea of the 2x10 rim with 2" ledger,2x8 joist and blocking. That shop will be solid as hell. Did a "boat shop" 18x27. Doubled the rims as well as the end joists .

Pic below 2x10, 16"oc, 3/4 non T&G deck. Town required 42"d piers. Poured a 12" deep by 16" diam conc foot than put a 2.5 CCA piling stub to ground level.Kept structure low to ground.Built a wood ramp, 6x6's with 5/4 pt decking to serve the 9'w x8'h front door.

Regularly receives a +6000lb Linc Navigator, GMC Yukon, boats with no issues.

 

[mike93lx]

Mike,
Like the idea of the 2x10 rim with 2" ledger,2x8 joist and blocking. That shop will be solid as hell. Did a "boat shop" 18x27. Doubled the rims as well as the end joists .

Pic below 2x10, 16"oc, 3/4 non T&G deck. Town required 42"d piers. Poured a 12" deep by 16" diam conc foot than put a 2.5 CCA piling stub to ground level.Kept structure low to ground.Built a wood ramp, 6x6's with 5/4 pt decking to serve the 9'w x8'h front door.

Regularly receives a +6000lb Linc Navigator, GMC Yukon, boats with no issues.

What combo of lengths did you use to build to the 27' total?

 

[Skiff Builder]

Got 20'ers which were cut to 18- +\- and 9' +\- in order for joints to fall on 4 evenly spaced bearing points.

In your case on skids, I might make the rims join right on one of the floor joists at the 8'/ 12' mark, if you couldnt get 20'ers. Spiked in with your inside blocking would be strong enough.

 

[theoldwizard1]

I don't get why anyone would ever use wood in contact with the ground, the skid style foundation doesn't make sense.

It is cheap and easy. If they are PT and resting on 4"-6" of gravel, they will last a long, LONG time.

In some locations, building on skids gets around a lot of building code because it is a "temporary" building.

 

[theoldwizard1]

I have a 12'x16' shed, all wood, and the floor joist are made out of 4x4's treated. The shed has been moved maybe 5 times since I've lived here. ....What ties it together though is treated tongue and groove flooring @ 3/4" thick.

Smart !

 

[theoldwizard1]

Most of it is all dependent on the soil/sod or whatever you are building on

BIG TIME !

Remove the sod. Lay down 4"-6" of "sharp" gravel. Compact it. The area should go at least 1' past the edge of the building in all directions.

I still say, start with 6x6 PT skid (three 2x6s nailed together; you could use two, but if you stand them up, you need extra bracing to make sure they don't move). Joists rest on these. The rim board really does not supply any support.

My biggest problem after all these years was that a big fat old woodchuck tunneled under it...dam rodent

But he's gone now and the tunnels are filled with stones. Wish now I had buried some screening around the perimeter

Screening works well, but if the shed is built UP OFF THE GROUND with a compact gravel base, so that light and air get underneath, no varmints will take up residence.

 

[readhead]

Having been in the shed building and delivering business for several years I’ll offer my insight. Up to 16’ long we use 6x6 PT skids. All of our skids are ground contact PT. From 16’ to 40’ we laminate four 2x6 with staggered joints and under the side walls we laminate two 2x6. Floor joists are 2x6 covered with 3/4 t&g plywood.

If you layout the center skids at 5’ oc, a shed standard, it can be moved later by any shed mover. I hope this helps. What I described is pretty typical construction in the industry. It must work since we can load a 16x40 on a trailer and drive it down the road.

 

[Farmall450]

Mike,
Like the idea of the 2x10 rim with 2" ledger,2x8 joist and blocking. That shop will be solid as hell. Did a "boat shop" 18x27. Doubled the rims as well as the end joists .

Pic below 2x10, 16"oc, 3/4 non T&G deck. Town required 42"d piers. Poured a 12" deep by 16" diam conc foot than put a 2.5 CCA piling stub to ground level.Kept structure low to ground.Built a wood ramp, 6x6's with 5/4 pt decking to serve the 9'w x8'h front door.

Regularly receives a +6000lb Linc Navigator, GMC Yukon, boats with no issues.

Nice looking shed. How did the cost of that floor with footer compare to a 4" slab?

 

[Farmall450]

It is cheap and easy. If they are PT and resting on 4"-6" of gravel, they will last a long, LONG time.

In some locations, building on skids gets around a lot of building code because it is a "temporary" building.

The only benefit I could think of.

 

[bigdav160]

In some locations, building on skids gets around a lot of building code because it is a "temporary" building.

The only benefit I could think of.

And exempt from property taxes in some States. It's treated like a travel trailer in my area.

 

[Skiff Builder]

Nice looking shed. How did the cost of that floor with footer compare to a 4" slab?

Thks Farmall,
I could not use a conc floor. Draw boats on floor,pickup those lines and transfer to sheet stock, glue/fasten assemblies, secure build jigs, etc. Also would make structure a "Garage" in my town. Development permit, drywells for drainage, paved driveway, etc$$$$$

Conc is king for most. My previous untreated wood floor shed in that location went 30 years. The trim of the new building is the old ones floorboards reused. Neq bldg will last longer- I'll be dead or not working.

Wood deck As built :
540' 2x10
(16) ACX ply
(24) 80# Sakrete
(12) 11" piling stubs- free
52 joist hangers/ nails
500' plastic sheet
1/2 yd gravel
16d & 8d Nails

$1550.00

For your 4" slab to suit my town req:
90' 12x18 footing 42" deep. 5+ yd conc
Forms for above
420 CMU stem wall
70 cap block
Mortar for above
10 yd gravel
500' plastic sheet
6 yd concrete slab
Reinforcements of choice.
Excavate 35 yd soil
Removal of excess
Trash pump -excavation dry
Machine rental
Backfill
Compaction of base
Machine rental

I'll let you price the above at your local rates.

Merry Xmas to All,Peace on Earth, Good will to Men,
SkiffBuilder

 

[u2slow]

I don't get why anyone would ever use wood in contact with the ground, the skid style foundation doesn't make sense.

Either pour a concrete pad or use deck blocks to lift it up off the ground. With deck blocks you can just space them closer together and take span problems out of the equation. Heck, you could just **** up two 10' boards in a block with a little scab to keep them together.

I'm on your page. I put deck blocks under everything. Also use scraps of roofing to prevent moisture wicking up from the concrete.

Its too damp here in the PNW. Unpainted lumber molds when I store it my covered car-port for over a month through the winter. Even creosote pilings and railways ties rot in this climate.