Knowing how to build a shed ramp comes down to one number most people get wrong: the slope. Pitch it too steep and a mower’s deck high-centers on the lip, the wheels spin, and you are stuck halfway with a running engine. A gentle ramp fixes that. Shed ramps are not governed by building code, but the 1:12 ratio used for wheelchair ramps, one inch of rise for every foot of length, makes a safe, easy target that keeps a riding mower, wheelbarrow, or ATV rolling in and out without scraping. You can run a little steeper for high-clearance gear, but past about 1:8 most low-deck mowers high-center. A ramp is the last piece of a storage shed build, the part that turns a finished building into one you can actually drive into. This guide covers the slope math, the right lumber and stringer size, how far apart to space the boards, and how to frame, deck, and fasten the ramp.
TL;DR: Build a shed ramp at roughly a 1:12 slope, one inch of rise for every 12 inches of run. Shed ramps are not code-regulated, but 1:12 (the accessibility-ramp ratio) is the easy, safe target for rolling equipment. Frame it from pressure-treated, ground-contact 2x6 or 2x8 stringers spaced 12 to 16 inches apart, then deck the top and fasten it to the shed.
Aim for about a 1:12 slope: one inch of vertical rise for every 12 inches of ramp length, roughly 4.8 degrees. Gentle enough for a riding mower or loaded wheelbarrow to roll up without scraping. Shed ramps are not required to meet building code or ADA accessibility rules, but 1:12 is the ratio set for wheelchair ramps, and it makes a safe, easy target for equipment too. You can build steeper, but past about 1:8 low-clearance decks high-center, and a wet ramp gets slick fast.
The math is simple. Measure straight down from the door threshold to the ground, then multiply that rise by 12. A shed floor 6 inches above grade needs a 72-inch run, which is a 6-foot ramp. At a steeper 1:8 that same rise needs only 48 inches, but it is harder on the engine and slicker underfoot. Go shallower if you have the room. If the rise gets tall, over about 30 inches, add a flat landing partway up.
Use pressure-treated lumber rated for ground contact, then size your stringers to the load. Stringers are the angled boards that carry the weight, also called ramp joists. A 2x6 stringer spans about 10 feet 4 inches at 16-inch spacing in #2 Southern Pine or Douglas Fir-Larch; a 2x8 reaches about 13 feet 1 inch under the same 40 psf load, per IRC R502.3.1 and the American Wood Council span tables. A shed ramp run is usually only 4 to 8 feet, far shorter than that, so the wood is rarely your limit. Load and rot are.
| Stringer (pressure-treated, #2 grade) | Max span at 16 in OC, 40 psf | Best for |
|---|---|---|
| 2x6 | 10 ft 4 in | Push mowers, hand trucks, bikes |
| 2x8 | 13 ft 1 in | Riding mowers, ATVs, heavy equipment |
Spans are IRC R502.3.1 and AWC values, Southern Pine and Douglas Fir-Larch No. 2, 40 psf live load; SPF runs a little shorter, with a 2x6 at about 9 feet 9 inches. A ramp run is far shorter than any of these, so for a ramp the load it carries and the stringer spacing matter more than the maximum span. For anything heavier than a push mower, default to 2x8. The extra depth resists flex under a heavy machine.
Space ramp stringers 12 to 16 inches on center. Use 16 inches for push mowers, carts, and bikes; tighten to 12 inches for riding mowers, ATVs, or anything over a few hundred pounds. Closer spacing carries more weight, because each board takes less of the load. When in doubt, add a stringer. One extra board is cheaper than a cracked deck.
Five steps take you from bare ground to a ramp you can drive on. Most people finish in an afternoon.
Three mistakes ruin most shed ramps. The first is rot. It starts where untreated wood meets soil, which is why ground-contact lumber matters so much: USDA Forest Products Laboratory specimens treated to standard ground-contact retentions had no failures after 39 to 45 years in the ground. The second is too much slope, which high-centers mowers and turns the ramp slick. The third is a bare, smooth deck. A wet plywood ramp in morning dew is a fall waiting to happen, so add traction strips.
Aim for about 1:12, one inch of rise for every 12 inches of run, gentle enough for mowers and carts. Shed ramps are not code-regulated, but 1:12 is the accessibility-ramp ratio and a safe target here too. Go a little steeper for high-clearance gear, but past about 1:8 low mowers high-center.
Use 2x6 at minimum. A 2x4 is too shallow to carry a riding mower without flexing, while a pressure-treated 2x6 spans about 10 feet 4 inches at 16-inch spacing per the IRC and AWC tables. Step up to 2x8 for heavy equipment.
Space them 12 to 16 inches on center. Use 16 inches for push mowers and light loads, and tighten to 12 inches for riding mowers or anything heavier. Closer spacing adds load capacity.
Pressure-treated lumber rated for ground contact. USDA Forest Products Laboratory testing showed those retentions can last decades in soil. Pair it with corrosion-resistant screws.
Get the slope right and the rest is plain carpentry. A 1:12 ramp, ground-contact lumber, and stringers sized to your load will roll a mower in and out for decades. Measure your threshold height this weekend, pick your stringer size from the table, and build it once. Your back will thank you.
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