Lips and Level Changes

NZ Building Code (D1/AS1 – Access Routes)

D1/AS1 recognises that abrupt changes in level are a major barrier. Two parts are especially useful for your “lip at an entrance” discussion:

• Vertical variation between adjoining surfaces (eg pavers/tiles/finishes) should be very small: max 3 mm for square edges, or 5 mm for bevelled edges.

• Threshold weather stops (a common “lip” at a doorway) are acceptable only if they project no more than 20 mm above the finished surface; above that, it should be treated like a ramp solution.

Practical translation: NZ’s compliance guidance strongly favours flush transitions, and where a “lip” is unavoidable, it should be minimal or treated as a ramped transition, not a bump.

NZS 4121:2001 (Design for access and mobility – including associated facilities)

NZS 4121 is often used alongside D1 and is very clear on thresholds:

• Accessible entrances should have a level threshold where possible.

• If a stepped threshold is unavoidable and the change is 20 mm or less, no ramp is required (but it should be visually contrasted).

• If the change is greater than 20 mm, a ramp is required, with gradient not steeper than 1:8 and going not more than 450 mm.

• For outdoor routes, transitions should be made without abrupt changes in level.

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Real world: what lip height can a powered wheelchair handle comfortably?

There isn’t one perfect number because it depends on:

• front castor size and load

• tyre type, suspension, speed control

• surface friction (wet/dry)

• approach angle

• user confidence and risk tolerance

But for public playground/park access, a safe, realistic guideline you can publish is:

Best practice for powerchairs (public space):

• 0–5 mm: generally comfortable if edges are clean and surfaces are firm (aligns with D1’s 3–5 mm guidance for surface transitions).

• 6–10 mm: may be manageable only if bevelled/ramped and the approach is straight-on (still not ideal).

• 10–20mm: frequently problematic for castors (especially if approached at an angle, or if the surface is wet/soft). If you must have this change in level, treat it as a designed ramp/transition, not a “bump”.

• >20 mm: should be treated as a ramp requirement under NZ guidance (and becomes a genuine access barrier for many powerchairs).

Why powerchairs are different than manuals: Manual wheelchairs can sometimes be tipped back and “popped” over a lip. A powerchair (often very heavy, sometimes well over 250 kg with rider) can’t be safely tilted and doesn’t have the same quick manual recovery options if a castor jams or slips.

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The approach angle problem (why “diagonal” makes it worse)

When a wheelchair hits a lip square-on, both castors meet it together and the chair stays stable.

When approaching at an angle:

• one castor hits first, the chair yaws/twists

• the second castor may strike awkwardly

• you can get a “castor stall” where the wheel turns sideways and jams

• The user may need multiple attempts (or assistance), which defeats independence

“A lip that is ‘fine’ head-on can become a barrier when approached diagonally — which is exactly how people enter real playgrounds.”

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Tight spaces: mid-drive powerchairs and manoeuvring

Mid-drive chairs can feel nimble, but tight spaces are still hard because:

• front and rear wheels track differently during a turn

• footplates/castors swing into corners

• any soft ground, camber, or edge creates a stall point

NZS 4121 provides helpful “space reality” numbers you can reference:

• 1500mm turning circle is used as a minimum in multiple contexts.

• Power mobility devices can be larger: motorised wheelchairs are commonly 600–760 mm wide and 1000–1130 mm long (unoccupied averages).

• It notes that larger turning space can be needed where there’s heavier use of motorised mobility (eg scooters).

Plain-English takeaway:
If the entry “pinches” or requires a turn immediately after a lip/threshold, powerchairs are far more likely to struggle — especially with mid-drive steering geometry and castors.