TECHNICAL INSIGHTS

The articles featured in Technical Insights are to prompt thought and discussion to assist our members' question and evaluate their understanding of the technical requirements of Australian Standards and other national/international source material. Technical Insights is to intended to provide background information, a different viewpoint, a perspective from an individual with lived experience of disability or to prompt further discussion and/or research by you as an access professional.

by Howard Moutrie

TIMBER DECKING

One of the most common questions asked relates to the accessibility of timber decking and, in particular, the gaps between the boards. Typically, the requirements for grates are applied in the absence of any other guidance. I thought it would be worthwhile to discuss this issue.

The gaps between the timber decking boards are provided principally to accommodate expansion and contraction of the timber but also aid in the extraction of surface water. I note that timber decking is not always timber, and the new synthetic products behave differently. The recommended spacing of the decking boards varies depending on the type of timber, the width of the boarding and the location. The variation is from 3 -7mm. The variations occur due to the properties of the timber, some timbers expand more than others, the size of board, a wider board will expand more than a narrower board and the location, the timber is more likely to expand and contact to a greater degree when the environmental conditions are extremely wet and hot, for example in far north Queensland. It is also important to recognise that timber decking may also include wide and thick timber boards in locations such as a jetty.

Under most conditions a gap of 5-6mm is sufficient for standard timber decking while synthetic wood decking is 5mm. Large boards on a jetty for example may need 10-15mm spacing as they also may need to address cupping and twisting in addition to expansion. I would suggest that we say that the maximum gap between decking boards is to be 6mm as this covers the majority of situations.

So, in terms of accessibility, what should we consider acceptable. It is worthwhile to reference the requirements for grates and pavers. I would consider that a max 6mm gap with a maximum surface level difference between adjacent boards of 3mm. This is consistent with the existing requirements for other surfaces and meets the requirements for standard timber decking. Larger decking boards, over a 150mm wide may require an increased gap. The gap may be increased to a maximum of 13mm, based on the requirements for grates, provided that, where the gap exceeds 8mm the boards shall run transverse to the direction of travel.

VISUAL IDENTIFICATION OF GLASS

Clause 6.6 of AS 1428.1 provides the requirements for “vision strips” as I like to call them. One of the requirements is that the strip provides a 30% luminance contrast with the surface on the other side. I have commented, previously, that this requirement hasn’t been well thought through, particularly with respect to the testing of the installation to verify the luminance contrast. The strip is viewed against the background, through the glass, but is this how it is intended to be tested? If this is the case, then the LRV reading of the background will be affected by

the qualities of the glass. If it is intended that the reading be done directly on the material, and not through the glass, a more realistic contrast will be achieved but I still question if this is a valuable result. I am sure we have all seen an installation where a heavily tinted glass has been used with a white strip, providing good contrast, but not necessarily meeting the requirements. For example, the floor finish may be a light colour so really the strip should be dark. I have seen an installation where an extremely dark tint was used, you couldn’t see through the glass, and a white floor on the other side. The vision strip was black and provided the required contrast with the floor but was completely invisible against the glass.

For this example, perhaps the fact that you couldn’t see through the glass, removed the need for the strip as a person with vision impairment couldn’t see through the glass and think it was an opening it. The Standard doesn’t allow this type of thinking, a Certifier will say it must contrast with the floor.

So is there another option? A European guideline has a different approach. It doesn’t require a single band which contrasts with the floor but 2 separate bands which contrast with each other. One strip is required at 900mm above the floor and the second at 1300mm above the floor. The bands are to have a 30 points LRV difference. Perhaps a similar approach could be used here. Because the strips and their contrast can be reliably tested, I believe that this format provides an improvement over the current requirement. I would think that this could be further improved by locating the strips adjacent to each other to improve the identification of the strips. Food for thought.

Another issue relates to a compliant strip. The Standard requires it to be solid and non-translucent. What it means to say is that it is opaque. This means that the you cannot see through the strip. A simple test that I use is that if I place my hand or other object directly behind the strip, it fails if I can see an image of the object. A more technical approach could be to measure the light transmission through the strip but I feel this has some issues. Firstly, it requires another piece of equipment to test but secondly, what is an allowable light transmission. From my own experiments, the amount of light which may be transmitted is dependent on the strength of the light source, thus, 50lux may be transmitted through an opaque surface under direct sunlight but under heavy shade the amount of light transmitted may be 5lux. Also, a light colour tends to radiate light whereas a dark colour does not. Again, my experiments found that a truly opaque blue film recorded a light transmission of 5 lux whereas, under the same conditions a truly opaque white transmitted 85lux. On this basis, I think the simple test for opacity is the best.

So, the testing procedure for the vision strips is a 4 step process:

1. Test for opacity

2. Test the LRV of the strip

3. Test the LRV of the floor ( or the secondary strip in the alternative proposal)

4. Calculate the contrast using the Bowman Sapolinski Equation

Finally, what constitutes glass that can be mistaken for a doorway or opening? AS1288 provides such a definition. Under Clause 5.4.2, the following are considered not capable of being mistaken for a doorway or opening:

a. The sight width of the glazing is less than or equal to 500mm

b. The sight height is less than or equal to 1000mm

c. The sill is 500mmor higher above the floor

d. The glazing is opaque, patterned or a leadlight

e. If there is a rail located with its bottom edge between 700mm to 1000mm above the floor

f. If the panels are louvre blades

g. If the glazing protects a difference in level of 1000mm or more

Although these conditions may be suitable for people with average vision, I would consider that a person with vision impairment would not be able to determine the difference in either f) and g) and for accessibility purposes, these exemptions should be removed.