Slip resistance of walking surfaces
About 45 New Zealanders die every year resulting from a fall on the same level due to ‘slipping, tripping or stumbling’. Injury from all types of fall is the major cause of hospitalisation for injury in New Zealand. These statistics show the importance of providing safe walking surfaces in buildings to protect building users from slipping and tripping.
Building Code Clause D1 Access Routes requires that access routes 'have adequate slip-resistant walking surfaces under all conditions of normal use.' Acceptable Solution D1/AS1 of the D1 Compliance Document in Paragraph 2 requires a friction coefficient of 0.4 for level access routes used by the public. For houses, this includes only the route to the main entrance. Table 2 of D1/AS1 lists the materials that are acceptable where a slip resistance of 0.4 is required.
It also shows the range of slip values that can be expected for the various materials.
Decks not on the route to the main entrance are not required to have a 0.4 slip resistance so decking timber can be laid profiled side down. However, exposed uncoated timber on the route to the main entrance will probably need to have some form of fixed weatherproof matting to provide slip safety.
The friction coefficient is established using the test method given in AS/NZS 3661: Part 1: 1993 Slip Resistance of Pedestrian Surfaces. Most common materials can meet this figure when dry, but few can when wet. A new version of AS/NZS 3661 has been published as AS/NZS 4586: 1999, but the 1993 version remains cited in D1/AS1. The new version of the Standard uses the same pendulum test method as the 1993 version, so the method of testing to establish safe materials remains the same.
The 1999 version of the Standard provides for the use of the 'ramp test' for shoe or barefoot slip resistance. It gives useful 'R' values for flooring that may be subject to oil and grease, such as in commercial kitchens and factory buildings, as well as for wet barefoot situations. If a designer proposes to use the 'R' value of a material as a method of satisfying Clause D1, the building consent authority would need to evaluate the proposal as an alternative solution because the ramp test is not referenced by D1/AS1.
AS/NZS 4586: 1999 should not be used without its associated guide, HB 197: 1999. The guide gives advice on comparing 'R' values with pendulum test results and lists acceptable 'R' values for different locations.
Adequate slip resistance of walking surfaces also depends on proper maintenance. Most materials become less slip resistant with wear, and applying waxes and polishes can reduce slip resistance. Therefore, building managers and homeowners should be aware of the importance of correct cleaning procedures. Timber outdoors usually needs scrubbing with bleach to remove slippery mould and dirt.