Confirmation before purchasing materials for decking/pergola roof

[DaKid]

I'm about to buy the materials for my decking roof, but just wanted to get a quick sanity check please, before doing so. I'll be buying box profile 32/1000 sheets and some purlins to support them.

My decking roof comprises 2x4 rafters of length 4450mm spanning a roof of 7210mm at 525mm centres.

The intention is to fit 2x2 purlins at 1100mm centres in 5 rows, and on top of that to fit seven 4.5m sheets of white 0.7mm 32/1000 steel box profile. I'm choosing to use seven sheets over eight because I don't want to have to cut them, and it's ok for a small gap at one end.

Does this all sound reasonable? Also, I'd welcome advice on how to choose between two different sellers of the sheets. The price difference is less than £20, so I'm curious if there is anything else I could use to decide between this one or this one?

Many thanks!

 

[Deluks]

Confused. Your rafters aren't as long as your span.

 

[scbk]

What length are the 4x2s spanning? Is it the 4.5m, or is there some support in the middle?

If you have a local SIG roofing you could ask them for a price on the sheets, they're part of Steadmans

 

[DaKid]

Sorry .... confusing terminology on my part. The rafters are 4.5m in length, and they are covering a roof that's 7m wide.

 

[DaKid]

What length are the 4x2s spanning? Is it the 4.5m, or is there some support in the middle?

There is no support in the middle.

 

[DaKid]

According to The Sagulator, just one of those rafters should be able to support the load of a single sheet ...