Understanding NZ slip codes for sloping surfaces
D1
NZ Building Code Compliance Document D1 outlines the maximum geometric gradients that constitute an Acceptable Solution.
D1 specifies how steep a ramp is permitted to be from an accessibility and design perspective.
Example: Table 3 limits the maximum gradient for an accessible ramp to 1:10 (10%), along with requirements for landings, handrails, widths, etc.’
AS 4586 Appendix F
AS 4586 Appendix F provides a method of determining the minimum slip resistance performance required for a given ramp gradient.
AS 4586:2013 Appendix F can be used to determine the minimum laboratory wet pendulum value (Slope Design Value) required for a surface intended to be used on that 1:10 ramp.
AS 4586:2013 Appendix F deals with determining the additional slip resistance required for sloping walking surfaces, including ramps and stairs.
Understanding how they work together
NZ Building Code D1/AS1 specifically refers to Appendix F for determining appropriate slip resistance at different slopes.
The principle is that as the gradient of the surface increases, so does the required friction. Therefore, the same flooring solution that is classified as an acceptable solution on a horizontal surface, may not meet the requirements on a sloped surface.
Appendix F provides the method/tables for relating the horizontal requirement to the slope.
Example:
|
Ramp/stair slope |
Gradient |
Dry COF requirement |
Wet SRV requirement |
|
1:20 |
5.0% |
0.45 |
45 |
|
1:14 |
7.1% |
0.47 |
46 |
|
1:12 |
8.3% |
0.49 |
48 |
|
1:10 |
10.0% |
0.51 |
50 |
|
1:8 |
12.5% |
0.53 |
52 |
In simple terms:
- NZBC D1 answers: "How steep can I build the ramp?"
- AS 4586 Appendix F answers: "If my ramp is this steep, what slip resistance should the surface achieve?"