| Primary value | 1:8 max ((12.5%)) |
| Applies to | Internal parking ramps (basement-to-ground or floor-to-floor) |
| Exceptions | Ramps with ≥ 9 m straight transition zone → 1:8 OK |
| Without transition zone (avoid bottoming-out) → 1:10 (10%) safer | |
| Transition Slopes → It is best practice to provide transition slopes of at least 3m length at the top and bottom, with a gradient half that of the main ramp (e.g., 1:16 for a 1:8 ramp) to prevent vehicle scraping. | |
| Curved/Helical Ramps → For curved ramps, the 1:8 slope is measured along the centreline of the travel lane. The inner radius will be steeper and must be checked to ensure it is manageable. | |
| Ramps for Persons with Disabilities → This rule is for vehicular ramps. Ramps for accessibility have a much stricter maximum slope of 1:12 as per NBC 2016 Part 3, Annex C-2.1. | |
| Measured as | Vertical rise : horizontal run of the ramp slab. Transition zones at top and bottom flatten this further. |
| Source | NBC 2016 — Part 3, Clause 7.11.7 ✓ Verified |
A slope steeper than 1:8 (12.5%) significantly increases the risk of a vehicle's undercarriage scraping the ramp surface, especially for cars with low ground clearance or long wheelbases. During monsoon season, excessive slopes reduce tyre traction on wet surfaces, posing a safety hazard and hindering vehicle movement.
While 1:8 is the maximum permissible slope, designers often prefer a gentler slope of 1:10 (10%) for user comfort. To prevent vehicle scraping, transition slopes (typically half the main ramp slope, e.g., 1:16) of at least 3m length are provided at the top and bottom of the ramp.