The shed designer now has a Floor: none choice. With it there are no skids, blocks, joists or subfloor. Each wall's bottom plate sits on a ground-contact pressure-treated 4x6, laid on edge on a full gravel pad, and the gravel is the floor. The plate itself is treated too, since it sits a few inches off the ground. If the roof hangs on a ridge beam, each gable post carries about half the beam's load straight down. So each post gets a concrete pier of its own under the timber: a 12" form tube on a 16" square footing, dug to the frost depth you set.
It is drawn, checked, priced and written into the build steps like any other choice. The floor framing sheet disappears, the foundation plan shows the timbers and piers, and the section and wall detail show the wall standing on its timber.
What it saves on the 8x12 starter (prices before tax, from the tool's dated listings):
| Framed floor (blocks on gravel beds) | No floor | |
|---|---|---|
| Lumber | $738 | $651 |
| Sheet goods (subfloor, roof) | $195 | $47 |
| Site prep (gravel, fabric, tamper) | $121 | $365 |
| Foundation and hardware | $238 | $287 |
| Siding, fasteners | $812 | $770 |
| Materials | $3,102.61 | $3,118.43 |
| Peak above the gravel | 10' 3/8" | 9' 4-1/8" |
So on the starter, leaving out the floor costs $15.82 more, not less. The floor framing and three sheets of subfloor come to about $235. But a floorless shed needs gravel under all of it, not a bed under each block, and a 14 x 10 ft pad 4" deep is about 2.5 tons of stone, $244 more than the starter's beds. The two post piers add about $50 over the blocks.
Two cases where it does pay:
- Against a framed floor on the same full gravel pad, no floor saves $196.48.
- With a ridge board and rafter ties instead of a ridge beam, there are no posts to put on piers, and no floor saves $61.20 against the framed version.
The peak drops by the floor's 8-1/4", which helps under a height limit.
The checks. Three screening checks stand in for the floor-joist, subfloor and skid rows:
- Timbers on the soil. On the starter the heaviest wall line is 206 lb/ft. Spread 2" each side through the 4" of gravel (7-1/2" wide), that is 22% of the 1,500 psf the IRC lets you assume for clay or silt (Table R401.4.1).
- Bottom plate bearing on the timber. The worst point load is the ridge-beam post on its two studs. It comes to 28% of the crushing strength across the grain (Fc⊥) of wet Southern pine No. 2 (565 psi x 0.67).
- Each post pier on the soil. The post's 1,099 lb plus the pier's own 373 lb of concrete reaches 55% on the footing.
None of this is engineered or code-checked. A timber lying on gravel along its whole length is not checked as a beam.
The catches. The tool says these out loud on the design:
- Damp. Gravel drains, but the ground under it stays damp and the shed air with it, so keep anything that rusts or mildews up on shelves.
- Animals. Rodents can dig under a timber where a floor would shut them out. Galvanized 1/4" hardware cloth under the gravel helps; it is not priced.
- The door step. The door keeps its timber as a 5-1/2" step, so a mower needs a ramp.
- Lap siding clearance. With lap siding the bottom course ends up 4-1/2" above the gravel, under the 6" that James Hardie and LP ask for, and the tool warns about it.
For a shed meant to match a house with lap siding, that last point is the deciding one.
Also new: a "most space between blocks or piers" setting (4 ft as before). The options table prices blocks or piers 5, 6 and 8 ft apart, and the skid check rules on each. On the starter's 4x4 skids, 6 ft fails the skid's bending check, so the 4 ft default stays.