Building a 12×20 shed follows nine stages in order — permits, site prep, foundation, floor and wall framing, roof, siding, doors, and finish work.
A 240-square-foot shed is a permitted structure in one town and illegal a mile away, and the only difference is a call to the building department before any dirt moves. Anyone mapping out how to build a 12×20 shed step by step arrives at the same nine stages, and skipping ahead usually means tearing finished work back apart. These specs come from published 12×20 plan sets and current kit listings.
Does A 12×20 Shed Need A Permit?
In most jurisdictions, yes — 240 square feet clears the size cutoff many counties and cities use to exempt small sheds, and published 12×20 plans state local building codes must be followed. No national rule exists, so the governing number is your own building department’s. Two details decide it: your area’s square-footage threshold and how close the shed sits to a property line. A five-minute call settles both; skipping it risks a stop-work order on a building you already paid for.
Plan style comes next, since it drives everything downstream. Common sets cover gable, gambrel, lean-to, field shed, and garden designs, each with a different roof, foundation, and material list. Treat those documents as build sequences rather than code references — the framing specs inside still need local review.
Site prep closes this stage: choose ground that drains away from the building, strip the grass, and square the corners by measuring diagonals. Matching diagonals mean true 90-degree corners.
Building A 12×20 Shed Step By Step: Foundation To Finish
Each stage carries the one above it, so the order is fixed: foundation, floor frame, walls, roof frame, sheathing and siding, roofing, openings, then trim. Two foundation styles dominate published 12×20 plans — pressure-treated skids and a poured concrete trench. Here is how the stages break down:
- Foundation. One plan specifies a trench about 1 foot wide and 1 foot deep, filled with concrete, then standard bricks laid over the cured footing. Others use 4×4 skids under the floor frame, faster and easier to re-level later.
- Floor frame. A 2×6 frame over the skids, topped with 3/4-inch plywood decking.
- Wall framing. 2×4 studs spaced 24 inches on center in the field-shed plan, with headers over every door and window opening.
- Roof framing. Identical trusses at even spacing, with pressure-treated rafters on the gable design. That plan’s finished shell measures 12 ft. 2 1/2 in. tall and 20 ft. 1 in. wide.
- Lean-to builds. The cut plan calls for 1 1/2-inch by 7 1/4-inch pressure-treated framing lumber and 11′-9″ joists.
- Siding and roofing. T1-11 panels fastened with screws or nails every 8 inches, then roofing over underlayment.
- Openings and trim. Hang the walk-in door last so the frame is settled, then add trim.
Check square again after the walls go up but before sheathing. When both diagonal measurements match, the frame is true and the siding panels line up without shimming.
What Does A 12×20 Shed Cost?
| Build Option | Listed Price | What It Covers |
|---|---|---|
| Best Barns Shedquarters 12×20 kit | $3,914.00 sale, $4,489.00 regular | 240 sq ft wood kit, barn doors, walk-in door |
| Entry-level 12×20 kits | From about $2,524 | Basic shell, plainer siding |
| High-end 12×20 kits | Up to about $9,768 | Upgraded siding and roof styling |
| Siding choice | Drives most of the spread | T1-11 versus basic panels |
| Roof style | Not in kit price | Gable, gambrel, or lean-to trusses |
| Foundation | Not in kit price | Skids, trench concrete, or brick piers |
| Site prep and permits | Not in kit price | Leveling, excavation, local fees |
Kit pricing swings by thousands for the same footprint, almost entirely from siding, roof style, and door count. Kits also exclude the foundation, the pad, and permit fees, which is why two neighbors with identical buildings can report very different totals. If you are still choosing a model, our tested 12×20 shed kit roundup compares options by price and included features.
The order never changes: lock the permit, level and square the pad, set the foundation, frame the floor, raise the walls, build the roof, then close it in. A kit changes who cuts the lumber, not the sequence.
FAQs
How Long Does It Take To Build A 12×20 Shed?
A precut kit typically goes up in two weekends with two people, since panels and trusses arrive sized. Framing from a plan set takes longer, often several weekends. Weather, inspection windows, and concrete curing add days, so treat any estimate as a floor rather than a deadline.
Can You Build A 12×20 Shed On A Concrete Slab?
Yes, if local code allows it. A slab works well for a shed tied down with anchor bolts through the sill plate and keeps the floor dry. The trade-off is cost and permanence — a slab cannot be re-leveled or moved, while 4×4 skids let you adjust the building later and suit most published plans.
What Size Foundation Does A 12×20 Shed Need?
Plan for a footprint slightly larger than 12 by 20 feet so siding and trim overhang the base. One published plan calls for a trench about 1 foot wide and 1 foot deep under the perimeter. Skid foundations use 4×4 pressure-treated runners under a 2×6 floor frame, and your building department has the final say on which method it accepts.
References & Sources
- Home Depot. “Best Barns Shedquarters 12 ft. x 20 ft. Wood Shed Kit, 240 sq. ft. (SQUASE20)” Source for the Shedquarters 12×20 kit price and listed specifications.
