# Forum More Stuff Debate & Technical Discussion  Wind Codes

## duncang

Hi, 
Just wondering if someone can explain how the wind code / terrain category system works?  I've done a little Googling and couldn't find anything that really summed it up. 
I've been getting quotes for a shed (6x7.6) in a residential area in Brisbane. 
One company quotes the Wind code as Region B, TC3 (W41)
Another says 'N3'
Yet another says 'Region W/S 49m/s, Terr: ES, Non-Cyclonic'. 
Are all these categories equivalent?  :Confused:  :Confused:   I want to make sure I'm comparing apples with apples  
Thanks 
Duncan

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## Stan 101

G'day Duncan,  
Basically the W41 is an old and obsolete code and hasn't, or shouldn't have been used for a good 10 years or so. The W codes were based on permissible loadings. W was designated wind speed and the number referred to wind strength in metres per second. 
The current windspeed codes are designated N1,N2, N3 and on for non cyclonic regions and C1, C2, C3 and on for cyclonic regions based on ultimate loadings. 
There are three ways of determining wind speed calcs baded on terrain and the like. Here is a great little tool I've just found to offer some insight:  Wind Rating Calculator 
Have a look there and go through the motions and it should offer ideas on region, terrain, shielding and the like. 
Cheers,

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## duncang

Thanks Stan - much appreciated. 
So on that basis I've worked out that the 3 are basically equivalent, with the variables being the assumed terrain category, topograhics etc. 
Thanks,
Duncan

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