Ramp slope, width, and landings, with the arithmetic

A ramp is a walk that is too steep to ignore. Under the 2010 ADA Standards, a walking surface can slope up to 1:20. Steeper than that, up to 1:12, it is a ramp, and it picks up rules for width, landings, handrails, and edges. Steeper than 1:12, it is usually the wrong ramp, with two narrow exceptions for existing sites that still will not get a wheelchair up a tall porch.

Private houses are not, as a class, required to build ADA ramps. The arithmetic is still the arithmetic. A ramp that is too steep becomes a slide in the wet and a hill the person cannot climb on the way back. This page does the inches. A building official decides the permit. A clinician decides whether this person should propel a wheelchair on a slope at all.

The only ratio that should be your default

Section 405.2 says ramp runs shall have a running slope not steeper than 1:12. One inch of vertical rise takes twelve inches of horizontal run. A porch floor 24 inches above the walk needs a 24-foot ramp before landings. A single step of 7 inches needs a 7-foot ramp. People are disappointed by this in week one and grateful in January, when a shorter, steeper ramp is ice with a handrail.

Section 405.6 limits a single run to 30 inches of rise. After that you need an intermediate landing and a new run. A full story, roughly 100 inches or more from floor to floor, is not a ramp project in a normal yard. It is an elevator or a life rearranged downstairs. Do not let anyone talk you into one long steep chute because the yard is short.

The existing-site exceptions in table 405.2 are easy to abuse. Where space is tight, a slope of 1:10 is allowed only for a rise of 6 inches or less, and 1:8 only for a rise of 3 inches or less. Those are short threshold solutions. They are not permission to run a 1:8 ramp up a 24-inch porch. At 1:8 that porch would be 16 feet long and far steeper than most wheelchair users and many walker users can manage safely. If the yard cannot hold 1:12, use a switchback, move the entrance to a lower side of the house, or use a vertical platform lift. The zero-step guide is the other honest option: change the ground instead of perching a ramp on it.

Width, landings, rails, and edges

Section 405.5 sets the clear width of a ramp at 36 inches minimum. That is clear, between handrails, not the width of the boards you bought. A 36-inch-wide deck with rails mounted on the inside face can lose several inches. Specify clear width in the contract.

Cross slope, the tilt from side to side, is 1:48 maximum under section 405.3. A ramp that drains by tilting sideways throws a wheelchair toward the edge. Slope the walking surface along the run, and handle water with the surface and the landing design, not with a sideways tilt.

Landings, section 405.7, are 60 inches long minimum and at least as wide as the ramp. You need one at the top and one at the bottom of each run. If the ramp changes direction, the landing has to be large enough to turn, and a 60-by-60 landing is the usual planning square. The top landing has to deal with the door. If the door swings out onto the landing, the landing has to be deep enough that the open door does not steal the maneuvering space. Measure the door swing on the ground with a tape before you pour footings. A landing that is a perfect 60 inches on a drawing and 48 inches once the storm door is open is a failed landing.

Handrails are required on both sides if the rise is greater than 6 inches, section 405.8. Height is 34 to 38 inches above the ramp surface, section 505.4. The gripping surface should be graspable, generally a round profile between 1¼ and 2 inches, not a flat 2x4. Rails extend horizontally 12 inches beyond the top and continue at the slope for 12 inches at the bottom in the ADA detailing, and they have to be continuous so a hand is not forced off at a post. Edge protection, section 405.9, keeps a caster from rolling off the side. A curb, a rail low enough, or a barrier within 4 inches of the surface is the idea. A pretty open side with no edge is a tip waiting for a wheel.

The surface has to be stable, firm, and slip resistant, section 302. Gaps in the direction of travel, such as deck boards with wide cracks, catch casters and cane tips. Section 302.3 limits openings. Leave drainage, but do not leave a half-inch slot in the direction of travel. Wood needs a broom finish or a traction strip when it is wet. Smooth painted plywood is ice when it is dry and worse when it is not.

A worked example

The porch floor is 21 inches above the sidewalk. The door swings out. The yard from the bottom step to the public walk is 28 feet.

At 1:12 the run is 21 feet. Landings want 5 feet at the bottom and 5 feet at the top, and the outward door may demand more than 5 feet at the top so the swing has a place to live. Call the top landing 6 feet to be safe until you measure the door. Total length is about 21 + 5 + 6 = 32 feet. The yard has 28. A straight ramp does not fit.

Options that still respect 1:12: turn the ramp along the house with an intermediate landing, if the side yard is long enough; raise the walk itself so the rise is no longer 21 inches, which is the zero-step approach; or use a short vertical lift at the porch and keep a stair for everyone else. Options that do not respect the user: a 1:8 ramp because the boards were already cut, a ramp with no rails because they "look institutional," or a portable channel ramp set out on rainy days and taken up at night. Portable ramps have a use for a van or a temporary step. They are a poor primary entrance if they move, lack edges, and live in the garage when someone forgets.

Write the rise, the run, and the landing sizes on the drawing. If a bidder's proposal does not restate them, the bidder has not designed a ramp. The bid guide shows what an itemized price looks like. The Joint Center for Housing Studies, citing older studies in 2015, put ramps and stairlifts in a reported typical range of $2,500 to $12,000. AARP's 2015 interviews described a simple sloped concrete walk to a door around $3,000 in one Texas market, and $15,000 to $35,000 when the work included walls, lighting, and a widened driveway. Those are dated reported examples. A switchback with footings and rails in a frost climate will not match a short concrete walk. Get local bids.

Winter, footings, and permits

A ramp facing north stays frozen. The porch and winter guide covers traction and lighting. Plan the maintenance when you plan the lumber: who shovels, where the snow goes, whether a roof over the run is worth the posts. An uncovered ramp is a part-time entrance.

Footings have to go below the frost line your code uses, or the ramp heaves and the slope you calculated becomes a twist. Attachment to the house has to be lagged into structure, not into a skirt board. Flashing has to keep water out of the rim joist. These are ordinary carpentry rules, and they are why a weekend ramp of unpainted lumber on deck blocks fails in year three and tilts in year one.

Most cities want a permit for a permanent ramp because it is a structure, and some accessibility programs will not pay for work done without one. Call the building department with the rise and the address before you buy lumber. A ramp that crosses a public sidewalk or changes a curb cut is not yours to build. That land belongs to the city. Stay on the private side unless you have an encroachment permit.

If the person cannot reliably use a 1:12 slope because of strength, a ramp is the wrong prescription even when the math fits. Say that early. A short rise might still want a ramp for a wheelchair pusher, who also has to make the grade. The pusher's strength is part of the design. A long ramp with no resting landing except the required ones can be exhausting. The 30-inch rise limit creates those rests. Do not stretch the runs to avoid an extra landing.

Ramp checklist

Before anyone orders lumber

• Measure the rise from the finished porch to the finished walk, in inches, at the door you will actually use.
• Multiply by 12. That is the run in inches. Add landings of at least 60 inches, more if the door swings onto them.
• If the total is longer than the yard, design a turn or a different entrance. Do not steepen past 1:12 except for the tiny rises in the ADA table.
• Clear width 36 inches between rails. Cross slope no steeper than 1:48.
• Rails both sides if the rise exceeds 6 inches, 34 to 38 inches high, graspable, with edge protection.
• Surface firm when wet, gaps too small for a caster, footings to local frost depth, permit pulled.
• A winter plan: who clears it, and a light at the top and bottom as the CDC asks for stairs.

A ramp is a success when the person uses it on an ordinary Tuesday, not when it photographs well on installation day. Walk it with the wheelchair or the walker that will live there, in the shoes that will be worn, before you pay the last invoice. If a caster hits the landing lip, that lip gets beveled now, under the quarter-inch rule in the floor and threshold guide.

Sources

• U.S. Access Board, 2010 ADA Standards, sections 302, 303, 405, and 505.
• CDC STEADI, Check for Safety, on stair lighting and objects.
• National Institute on Aging, Home safety checklist.
• Joint Center for Housing Studies, Aging in Place: Implications for Remodeling (2015).
• AARP, Home Remodeling and Improvement Costs (2015).
• International Code Council, International Residential Code, as adopted locally, for footings and exterior stairs.