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Hi Guys, I have a pair of the 20 foot shipping containers and would like to build a steel roof over the containers which will be 6 meters apart.
I'm wondering for rain runoff and water collection is there a minimum amount of pitch suited to rain runoff.
The containers are on a Gemstone mine claim and don't have to be built using any building code and the structures don't require any council approvals.
Attachment 479020
It depends on what the rainfall and general wind conditions are like in your area.
I believe that 5 degrees is the legal minimum, but IMO for most conditions that's way too flat.
If most of your water collection is expected to be roof dew, then you probably want around 20 degrees. Especially in a dusty area with infrequent rainfall. It sounds excessive, but the dust settling on the roof needs to washed off by the dew, else it'll build up and promote lichen growth and similar which seriously reduces the amounts collected.
With frequent light showers you can drop that back a bit, to maybe 10-15 degrees. (You could go to 5 degrees but I reckon that's asking for trouble. Go that flat and a spider sneeze from the wrong direction could blow the water uphill and under the capping!)
If you mainly want to collect infrequent but heavy showers, I'd probably go t'other way and make it 25 or more.
Basically, the steeper the slope the better the water collection and the stronger the wind needs to blow from the side before the water runs the wrong way.
It's all subjective... and the above figures are simply based on my experiences throwing together bush shacks. I like 20 minimum 'cos it avoids so many other headaches. ;)
Is there a particular reason you want a ridge?
By far the cheapest and easiest way is a skillion roof and refer to the manufacturers recommendations for minimum pitch of your selected roof profile. It can be as low as 2 degrees for some concealed fixed roof profiles
Be careful that you have sufficient pitch I have a pergola with six meters of width and its a pain when the rain is heavy I have raised it by approx. 200mm and it still is a pain. You should be able to get pitch recommendations if you google it, good luck.
I worked at a site in the Pilbara a few years ago that had an arrangement pretty well as you're proposing. It wasn't used to harvest rainwater and I don't think rain blowing back under the ridge capping was an issue because the roof was more for shade when doing machinery maintenance. From memory the pitch was 12 degrees. Shouldn't the upper measurement in your diagram be 5.4 M?
Cheers,
Geoff.
I second that. If you look at instances where roofs are blown off by cyclones and storm winds, skillion roofs suffer more damage than steeper pitched roofs.Quote:
Originally Posted by Skew ChiDAMN!!
An airline pilot friend explains it as follows.
- "Its all about lift and angle of attack.
- A tiger moth has an angle of attack of five degrees, and takes off at 30 knots.
- A roof is no different."
The upside to having a steeper roof is having more room above the containers to store junk.....useful things for future use.
Pete
well, all good, maybe.Quote:
Originally Posted by Specialized29er
The engineer left in me suggests that although Council approval (aka does the structure conform to the local design criteria) is not required and following building code (aka conforming to accepted practice) is also not a requirement, you would be well advised to at least read the Building Code of Australia. The BCA contains a distillation of what is considered best practice across the country with chapters about cyclonic wind and accompanying uplift, etc. My memory from 45 years ago, recalls that wind uplift forces vary by a factor of about 5 depending on the fetch of the wind's approach direction.
Now if you don't mind replacing the roof after every smallish blow, you can skip the bit about reading the BCA, but if you want your roof to last and generate run-off water, then at least reading the BCA's bits about wind forces and uplift would be a very good starting point.
The simplest advice - copy others!
Rural Container Sheds. Shipping Container Sheds - Container Traders, Australia
A very quick Google search comes up with some great links that provide plenty of construction detail. Do another Google search for "shed components" for access to the myriad of manufactured items available to build a shipping container roof.
Ezy Engineering | Ezy Roof
Shed Components | Steel Sheds in Australia
A real gold mine (pardon the pun) of info here with guidance on wind regions, span tables etc
:: Span Tables
https://www.purlinbrackets.com.au/fi..._Farm_v2.0.pdf
No requirement to read the BCA plus the manufacturers have already done the engineering for individual components. Your challenge is to select the right bits "This goes with that at ...."