Reflecting on Reflectivity

Posted on : April 6, 2011

Shedeye has questioned the ambiguity of the SEPP definition of “low reflectivity” and is going to expand more on this.  This article will explain the standards and map them to each other.  For a complete discussion go to the Shedeye Investigator  article.

The current requirements of reflectivity standards of metal cladding as seen in BASIX, BCA and SEPP all seem too ambiguous for correct applications and on site judgement and analysis. As explained below, the variations of each of these regulatory bodies will be apparent especially in the Class 10a or domestic shed/ garage construction and manufacturing industry. What are solar absorptance, reflectivity, gloss levels, heat transfer calculations, R Values, BASIX Scale, BCA Scale, and visual acceptability? All these factors play a role in the decision of colour choice (or ZINCALUME ®) of your shed metal cladding and roofing.

The standard by each authority vary and will cause some problems within the industry along with questions for the Building Certifier during the approval process. These variations on the choice of colour may affect the outcome of approval depending on which code is followed and whether or not the local council regulations agree or disagree with these codes.

Why is there a contradiction among something on coloured steel cladding when each colour has its own Solar Absorption Index Value? The reason for this is simple – each building (Class 10a) should be inspected individually prior to this decision of colour being made, to evaluate the different aspects of the codes above and the influence each requirement has on the following:

  • Visual Suitability (impact on neighbours)
  • Environmental Considerations (energy saving)
  • Personal choice (What colour you want?)
  • Building use (aspects of comfort levels within the building)
  • Building position (in reference to location of other building and aspect of sunlight etc)
  • Local Council requirements (necessary for approval)

 

Shedeye Reflectivity Scale Comparison Chart

 

Colour Colour Solar Absorption SEPP Classification BCA Classification BASIX Classification
STEEL COLOURS
Classic Cream ™ 0.31 Not Acceptable VL L
Surf Mist ® 0.318 Not Acceptable VL L
Paperbark ® 0.421 Not Acceptable VL L
Evening Haze ® 0.427 Not Acceptable L L
Shale Grey ™ 0.433 Not Acceptable L L
Sandbank ® 0.455 Not Acceptable L L
Dune ® 0.466 Not Acceptable L L
Windspray ® 0.584 Acceptable D M
Pale Eucalypt ® 0.597 Acceptable D M
Bushland ® 0.619 Acceptable D M
Headland ® 0.632 Acceptable D M
Wilderness ® 0.651 Acceptable D M
Jasper ® 0.682 Acceptable D M
Manor Red ® 0.688 Acceptable D M
Woodland Grey ® 0.706 Acceptable D D
Loft ® 0.711 Acceptable D D
Monument ® 0.732 Acceptable D D
Ironstone ® 0.743 Acceptable D D
Cottage Green ® 0.746 Acceptable D D
Deep Ocean ® 0.749 Acceptable D D
PLAIN
Zinalume ® ? 0.35 Not Acceptable VL L
METALLIC
Citi ® ? 0.55 Not Acceptable L M
Axis ® ? 0.55 Not Acceptable L M
Conservatory ® ? 0.55 Not Acceptable L M
Skybridge ® ? 0.55 Not Acceptable L M
Cortex ® > 0.55 Acceptable D M
Facade ® > 0.70 Acceptable D D
COOLMAX
Whitehaven ™ Not Acceptable VL L

 

As this spreadsheet describes the colours taken from the BlueScope website and lists four factors that are currently used in the building industry. How these play a part in colour choice for metal cladding on these buildings requires an understanding of each of the columns above. There are as follow:

  • Column 1. This is simply the list of ColorBond Colours, ZINCALUME and Metallic Colours from BlueScope.
  • Column 2. The Solar Absorption is simply a numerical index that shows the amount of solar “radiation” that is absorbed by that particular colour. This is not to be confused with reflectivity and the two are not inversely proportional to each other.
  • Column 3. SEPP is the body of government in NSW that has legislated the requirements of colour to be used in Class 10a buildings. The requirement is based on reflectivity and although not exactly stipulated – it only accepts Medium or Dark colours (low reflectivity).
  • Column 4. BCA has its own version of classification of colours in this list and refers to Very Light (VL), Light (L) and Dark (D).
  • Column 5. BASIX is the New South Wales Building and Sustainability Index body with its own colour classification and is as follows: Light (L), Medium (M) and Dark (D).

 

BASIX Solar Absorptance Scale

The BASIX scale is based on the following and is linked directly to the value of solar absorption index.

This can be located at http://www.basix.nsw.gov.au/docs/ under Thermal Comfort Protocols.


The Building Code of Australia (BCA) Colour Classification.

BCA has classified roof colour also on the basis of their solar absorptance, and referred simply as light, very light and dark. Very light is below 0.425 solar absorptance, Light is below 0.550 solar absorptance and Dark is above 0.550.

 

SEPP Colour Acceptance Scale.

This is quite simply stated as must be “low reflective material”. Being low reflective can only be Dark on the BCA Scale or Medium and Dark on the BASIX Scale. For the purpose of this investigation – the BCA scale has been used as this code is generally utilised by all local councils and Building Certifiers. The problem is not the cut off area – but simply in the statement of “low reflective material”.


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4 Responses to “Reflecting on Reflectivity”

  1. ROOFER said...

    Hi Shedeye,

    What an article on Roofing Reflectivity – Can the ROOFER include this link to the SHEDEYE INVESTIGATOR ARTICLE in the Roofing Blog? This is not only applicable to the shed industry – but to the roofing industry in general.

    Congratulations on this INVESTIGATION! Once again outstanding!!!!

    THE ROOFER.

  2. Shedeye said...

    Hi Roofer,

    Yes you can provide a link to this article. Thanks for the compliments!

    Keep your eye on the site, as there is a great deal of very useful articles that will be published soon.

    Kind Regards,
    Shedeye.

  3. glare off new colorbond roof said...

    […] is a complex subject – here is one article that may help? The problem with colour – especially white is the reflective index that is determined […]

  4. colorbond roofin' said...

    […] affect the temperature especially in summer. See this BlueScope PDF or an independent study here Reflectivity. See me at The Roofer and I love visiting and at Shedeye Reply With Quote […]

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