Correct Site Classification

November 18, 2015

The Steel Shed Industry has come a long way in the last decade in understanding and utilising design codes applicable to sheds.

In most cases, wind forces will generate the major loads a shed is required to withstand for the design life of the structure.

Whilst historically, the industry only used a few standard wind speeds based on generic designs (and some still persist in doing this ) the rest of the industry has come to understand the benefits of engineering and software that provides for a large range of wind speeds and can generate a site specific certification.

So why is it so important to get the correct site wind speed?

The customer generally has no appreciation of wind speeds or the wind energy that will be applied to their shed. We often hear reports of 100k/m winds on the evening news, 100k/m is a very low wind speed, in fact the code starts at 106km/h

If you are living on a farm, then typically the design wind speed will be in the order of:

  • Region A 40m/s = 145km/hr
  • Region B 50m/s = 180km/hr
  • Region C 60m/s = 220km/hr
  • Region D 85m/s = 300km/hr

Hint : To convert m/s into km/hr, simply multiply by 3.6

The big issue is that the wind speed is squared to obtain the pressure that is being applied to a building by the wind. (see graph below)

Wind Speed for Sheds

Too high a wind speed and your building cost will unnecessarily increase.

Too low a wind speed and your building will potentially fail in less than a design event and an insurance company may not pay out on a claim as the building was not “fit for purpose.”

Shed sellers should consider the site factors before generating a customer quote.

A common error often seen is shed sellers providing a quote based on a standard program pre-set ie TC2.5 Partial Shielding. In many cases the terrain category isn’t correct and THERE IS NO SHIELDING.

The online ShedSafe building specification module (which all accredited sellers are required to complete annually) provides guidance on how to determine the correct site classification.

From 1st December 2015 the site classification for orders will be checked by each manufacturer.

ShedSafe buildings are specified by a range of Government and Statuary authorities as they are seeking to purchase a shed with BCA compliant engineering and a site specific certification for the Shed with correct Importance level and Wind speed classification.