IRC R311.8 slope and landings, quoted with the edition read
A ramp is one division: rise over slope gives run. What catches people is everything the code adds around it. R311.8.2 requires a 3 ft by 3 ft landing at the top, at the bottom and at every change of direction, and those are additional to the run, not part of it. A 30 in rise at 1:12 is 30 ft of ramp and 36 ft of yard.
Ramp geometry
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ft
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Slope and landing figures from IRC R311.8, quoted below with the edition read.
Specification summary
Generated from on .
Reopen that address to reproduce these figures exactly.
Entered
Result
Ramp rise, run and the landings at each end
Prices for decking materials and labor
The published figures for decking materials and labor are on the deck cost estimator, with the byline, the publication date and the caveats that go with them. They are not repeated here, because the same table on two pages is worth less than one table you can find.
Worked example
A deck 30 in above the ground, ramped at the 1:12 maximum, 3 ft wide, running straight out with no turns.
Run. 30 in of rise at 1:12 is 360 in, or 30 ft of ramp. This is the only part most calculators do.
Landings. One at the top and one at the bottom, 3 ft by 3 ft each: 6 ft more.
Total.36 ft of yard, for a deck 2 1/2 ft off the ground.
Turn it. Add one change of direction and that is a third landing, another 3 ft, and a switchback that fits a smaller garden.
Handrails. At exactly 1:12 R311.8.3 does not require them, because it says exceeding 1:12. Fit them anyway.
Thirty-six feet surprises people, and it is the number that decides whether a ramp is possible at all. Switch to 1:8 and the run halves to 20 ft, but so does the chance of a wheelchair user getting up it unaided.
The formula
One division, then the code adds to it:
run = rise × n landings = 2 + turns total = run + 3 × landings
rise
total vertical, in
n
the horizontal units per vertical unit: 12 for a 1:12 ramp
turns
changes of direction, each of which needs its own landing
3
landing length, ft. R311.8.2 sets a 3 ft by 3 ft minimum
Landings are additional, never part of the run, and a door opening onto the ramp needs one too even where there is no turn. That is the term that makes real ramps longer than planned ones.
Which edition, and why it matters here more than usual
The ramp slope rule changed between IRC editions, and this is not a trivia point. The 2015 wording quoted below sets one maximum of 1:12 with an exception at 1:8 where compliance is technically infeasible. The 2021 edition restructured the section to distinguish the ramp serving the required egress door, which stays at 1:12, from other ramps, which are permitted 1:8.
The 2021 text could not be read from a document reachable from here, so this page quotes the 2015 wording it could verify and tells you to confirm your own edition rather than presenting one as universal.
For most people building a deck ramp the distinction is academic, because the honest answer sits below both: 1:8 is very difficult for a wheelchair user to self-propel, and 1:12 is the figure the accessibility standards settled on for good reason. If the ramp is for someone who uses a wheelchair, build 1:12 or gentler whatever the code permits.
The IRC is also not an accessibility standard. A ramp built to the ADA has further requirements, including a maximum 30 in rise per run before a landing is required regardless of turns, edge protection, and a cross slope limit. None of that is on this page.
Slope, landings, and which code edition you are under
Ramps shall have a maximum slope of 1 unit vertical in 12 units horizontal (8.3 percent slope). Exception: Where it is technically infeasible to comply because of site constraints, ramps may have a maximum slope of one unit vertical in eight horizontal (12.5 percent slope).
Lower Macungie Township, Pennsylvania, residential ramps handout, 2015 IRC
Check your edition before you build. The 2021 IRC restructured R311.8.1. Rather than one slope with an infeasibility exception, it distinguishes the ramp serving the required egress door, which keeps 1:12, from other ramps, which are permitted 1:8. That text could not be read from a fetchable document here, so this page quotes the 2015 wording it could verify and tells you to confirm which edition your jurisdiction has adopted. If you are building for a wheelchair user, design to 1:12 regardless of what the code permits.
Landings are not optional and they are not small:
A minimum 3-foot-by-3-foot landing shall be provided: 1. At the top and bottom of ramps. 2. Where doors open onto ramps. 3. Where ramps change direction.
R311.8.2, landings required
Three feet by three feet at the top, at the bottom, wherever a door opens onto the ramp, and at every change of direction. A switchback ramp needs a landing at the turn, and that landing is in addition to the run, which is why the total footprint is always larger than the slope arithmetic suggests.
Handrails shall be provided on at least one side of all ramps exceeding a slope of one unit vertical in 12 units horizontal (8.33-percent slope).
R311.8.3, handrails required
Note the trigger: handrails are required on ramps exceeding 1:12. A ramp built exactly at 1:12 is at the limit, not over it. Most people building a ramp for a wheelchair user fit handrails anyway, and should.
Where the ramp actually has to go
The run above is a length. Fitting it on a real lot is a different problem, and it is the one that stops most ramps being built as drawn.
The run is measured horizontally, so it eats yard, not deck. A 30 in rise at 1:12 is 30 ft of horizontal run before any landing is added, which on a typical suburban lot is most of the distance from the door to the property line. That is the number to check first, with a tape, before anything else on this page matters.
Turning costs a landing, and the landing costs area. A switchback folds a 30 ft run into roughly two 15 ft legs, which fits far more lots, but the turn needs its own landing and the two legs need space side by side. A turn is not free length; it is a trade of length for width plus a landing.
The door at the top needs a landing whether or not the ramp turns. A ramp that runs straight off a threshold gives you nowhere to stand while you open the door, which is precisely the moment somebody in a wheelchair needs level ground.
And the bottom has to land on something. A ramp ending on grass ends in mud by the second winter. The bottom landing wants to be on the same hard surface as the path it joins, and that is usually a small slab nobody costed.
IRC and ADA are different documents with different jobs
This page reads the IRC, which is the code that governs a residential deck ramp. If the ramp is for somebody specific, that may not be the document you want.
The ADA Standards are stricter in places and do not apply to a private home. They govern places of public accommodation and commercial facilities. A ramp on your own house is outside their scope, so nothing forces ADA compliance on it and nothing prevents it either.
Building to the stricter document is usually the right call anyway, because the reason for the ramp is a person, not an inspection. Where the two differ, the ADA figure is the one derived from testing how people actually propel a chair, and the extra cost of the stricter geometry is mostly length, which is space rather than money.
The exception is where space genuinely does not exist. A steeper ramp that gets built and is usable with help beats a compliant ramp that is never built, and that is a judgment for the household rather than for a calculator. What the page will not do is pretend a steeper ramp meets a standard it does not meet.
If the ramp is going in because of a specific person's chair and strength, an occupational therapist is worth more than either document. They will tell you the slope that person can manage, which is the only figure that matters here.
Frequently asked questions
What is the maximum slope for a residential ramp?
1 unit vertical in 12 units horizontal, an 8.3 percent slope, under IRC R311.8.1 in the 2015 edition, with an exception permitting 1:8 where 1:12 is technically infeasible because of site constraints. The 2021 edition restructured this, so confirm your edition.
How long does a ramp need to be for a 30 inch rise?
Thirty feet of ramp at 1:12, plus a 3 ft by 3 ft landing at each end, so 36 ft in total. At 1:8 the ramp is 20 ft and the total 26 ft, but 1:8 is steep enough that most wheelchair users cannot self-propel it.
Do deck ramps need landings?
Yes. R311.8.2 requires a minimum 3 ft by 3 ft landing at the top and bottom of every ramp, wherever a door opens onto the ramp, and at every change of direction. Landings are additional to the run.
When does a ramp need handrails?
R311.8.3 requires handrails on at least one side of ramps exceeding a slope of 1:12. A ramp built exactly at 1:12 is at the limit rather than over it, so the clause does not strictly bite. Fit them anyway if the ramp is for a wheelchair user.
Does a ramp need a guard?
Where the ramp walking surface is more than 30 inches above the grade below, yes, under R312.1.1, the same rule that applies to the deck itself. Ramps are named explicitly in that section.
Is an IRC-compliant ramp the same as an ADA ramp?
No. The IRC is a minimum for a dwelling. The ADA adds a maximum 30 inch rise per run before a landing, edge protection, cross slope limits and handrail extensions. If accessibility is the point, design to the accessibility standard.
Can I build a ramp steeper than 1:12 if I have no room?
The 2015 IRC permits 1:8 where compliance with 1:12 is technically infeasible because of site constraints, which is a judgment your building official makes rather than you. A switchback with a landing at the turn is usually the better answer than a steeper ramp.
Check these numbers yourself
IRC R311.8 RampsLower Macungie Township, Pennsylvania, reproducing the 2015 IRC. Used because codes.iccsafe.org returns HTTP 403.
How every figure here is verified: Sources & Method. Who builds this: Lucas Pradella, and the method is on About. Found something wrong? Tell us and it gets fixed or removed.
Figures on this page last checked against the source documents on 2026-09-07. Codes are amended locally; confirm against the edition your jurisdiction enforces.
Confirm your code edition. The ramp slope section was restructured between the 2015 and 2021 IRC and this page quotes the 2015 wording it could verify. The IRC is a dwelling minimum, not an accessibility standard. If the ramp is for a wheelchair user, design to 1:12 or gentler regardless.