20x20 Metal Building With Slab: Cost Breakdown
A 20x20 is 400 square feet — a single-bay garage, a compact workshop, or a storage building. It is the smallest footprint where a full red-iron metal building still makes economic sense, and it sits right at the boundary where some buyers should honestly be considering a prefabricated shed or a carport instead.
We will be direct about that below, because at this size the fixed costs of a permanent engineered structure are a large fraction of the total. If you need a permanent, permitted, code-compliant building, here is exactly what it costs and what the foundation involves.
What a 20x20 Actually Costs, Line by Line
20′ × 20′ = 400 square feet. The ranges below are typical 2026 market costs from building suppliers and concrete contractors — they are not SteelReady quotes. Regional pricing, design loads, and specification move every line.
| Line Item | Per SF | 20x20 Range | What Moves It |
|---|---|---|---|
| Building kit (delivered) | $12–$24 | $4,800–$9,600 | Gauge, eave height, doors, insulation, snow/wind loads |
| Concrete slab + footings (installed) | $9–$17 | $3,600–$6,800 | Thickness, rebar, vapor barrier, site prep, minimum-load delivery fees |
| Erection labor | $6–$12 | $2,400–$4,800 | DIY vs. crew, site access, minimum crew day rates |
| Site prep, permits & misc. | $4–$9 | $1,600–$3,600 | Grading, utilities, permit fees, engineering |
| Turnkey total | $31–$62 | $12,400–$24,800 | Everything above, combined |
Note the foundation engineering is not in the table above — it is a separate, published, fixed fee. See below.
Why Two 20x20 Quotes Can Be $20,000 Apart
The per-square-foot cost looks bad, and that is real. Four hundred square feet cannot absorb fixed costs. Permit fees are the same as for a building five times the size. A concrete truck has a minimum load charge. An erection crew has a minimum day rate. Engineering is a fixed deliverable. Spread across 400 square feet, all of that produces the highest unit cost of any size in this lineup — while still being the lowest total.
Ask yourself whether you want 20x30 instead. Because the fixed costs are already paid at 400 square feet, adding 200 more square feet typically increases the total by far less than 50 percent. Almost nobody regrets the larger building; a lot of people regret the smaller one. Price both before deciding.
A shed or carport may be the right answer. If you do not need a permitted, insulated, permanent structure — if this is lawn equipment storage — a prefabricated shed or an open carport will cost dramatically less and may avoid the permit entirely. We would rather tell you that than sell engineering you do not need.
If you do build it, it still needs a permit. Four hundred square feet is above the exemption threshold in most jurisdictions, particularly for a structure on a permanent foundation.
Concrete for a 20x20 Slab
A 20x20 slab is 400 square feet with 80 linear feet of perimeter. A 4-inch slab field is roughly 5 cubic yards; with a thickened edge, most pours run 7 to 8 cubic yards — a single truck, well under a full load.
Note that most ready-mix suppliers charge a short-load fee below a certain volume, commonly around 8 to 10 yards. On a pour this small that fee can be a meaningful percentage of the concrete cost, so it is worth asking about when you get quotes.
At this footprint a monolithic thickened-edge slab is nearly always the appropriate foundation, provided soil bearing is adequate. Loads are low, the perimeter is short, and separate spread footings are usually unnecessary.
The slab still needs a properly prepared and compacted subgrade, a vapor barrier if the space will be conditioned or used as a shop, and reinforcement sized for the actual conditions. Small does not mean casual.
What the Foundation Has to Do at 20x20
Uplift is essentially the entire design problem. A 400 SF metal building weighs very little. In most of the country, the wind uplift generated on that roof exceeds the structure's dead weight by a comfortable margin. What keeps the building on the ground is the mass of the concrete and the soil engaged by the footing. Footing dimensions here are typically set by uplift resistance, full stop.
This is why anchoring matters so much on small buildings. The failures you see photographed after windstorms — small metal buildings peeled off their pads and deposited in a neighbor's field — are almost always anchorage failures, not structural failures of the steel. The frame was fine; the connection to the ground was not.
Edge distance governs the turndown width. With a short perimeter and a thickened edge, anchor bolts are close to the slab edge. ACI 318-19 breakout capacity is highly sensitive to edge distance, and satisfying it usually sets the minimum width of the thickened edge.
Frost depth still applies. The turndown has to reach below the local frost line. In northern climates that requirement, not the load, determines how deep you dig.
A 400 SF building falls in our Up to 5,000 SF tier at a published rate of $0.40/SF. That covers the PE-stamped foundation plan set, full ACI 318 anchor bolt design, the complete calculation package, and revisions — always included, no limits.
Final pricing varies with location, scope, and revisions beyond the baseline. Send your reaction tables and anchor bolt plan and we will quote the exact number before you commit.
What People Build at 20x20
- ▸Single-bay garage
- ▸Compact workshop
- ▸Lawn and garden equipment storage
- ▸Motorcycle or ATV storage
- ▸Well house or utility building
20x20 Metal Building Questions
- How much does a 20x20 metal building with a slab cost?
Turnkey, most 20x20 projects run roughly $12,000 to $25,000 in 2026. The total is the lowest of any standard size, but the per-square-foot cost is the highest because fixed costs — permits, delivery, minimum crew rates, engineering — do not scale down with the footprint.
- Is a 20x20 metal building worth it versus a shed?
It depends what you need. If you want a permanent, permitted, insulated structure that will last decades and add assessed value, a metal building is a different product from a shed and the cost reflects that. If you need somewhere dry to keep a mower, a prefabricated shed or carport will cost far less and may not require a permit at all.
- How much concrete does a 20x20 slab take?
About 5 cubic yards for a 4-inch slab field, and roughly 7 to 8 cubic yards with a thickened edge. Ask your supplier about short-load fees — most charge one below about 8 to 10 yards, and on a pour this size it is a noticeable share of the cost.
- Do I need engineered drawings for a building this small?
In most jurisdictions, yes — permit requirements are driven by whether the structure is permanent and how it is classified, not by whether it is small. A 400 SF building on a permanent foundation typically requires a permit with PE-stamped foundation drawings. Confirm with your local building department, since thresholds vary.
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Background
- Metal Building Foundation Engineering Cost (2026)Foundation engineering for metal buildings costs $1,000–$11,000+ from traditional firms. Learn what drives pricing and how to get PE-stamped packages for less.
- What's Included in a Foundation Engineering Package?A breakdown of every deliverable inside a PE-stamped metal building foundation engineering package — plans, calcs, details, and what to look for.
- Foundation engineers by state →
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