Decking roofing

[DaKid]

Hiya. Hoping for some advice on roofing, please. I built this deck a couple of years ago ...

... and am very happy with it, for the most part. We put some bamboo matting on top to give us some shade, and it's honestly performed the job quite well. In the recent winds though, it suffered quite badly and so it's got me to thinking about something I was wanting to do first time, but for time and money reasons didn't get around to.

Specifically, I was wanting to add green, bituminous, corrugated roofing on top, in order to give even better shade and also a measure of protection from Summer showers. I did have a couple of questions, though, that I'd love to get some more expert advice on, please?

Low roof pitch
The pitch of the roof is very low (just under 4 degrees), but given that previously I had bamboo matting, it's obviously not really a concern to me about water leakage! Having said that, are there any other things that I'm unaware of that I should be considering regarding this low pitch, especially anything that would dissuade me from using corrugated sheets on it?

Purlins?
Would it be possible to add the sheets directly onto the rafters that I have there currently? They are just over 500mm centres, and I was intending (probably anyway) to add noggins to them to strengthen everything. I do not know much about the properties of corrugated sheets ... how much do they need this lateral support, i.e. purlins? What happens if I don't add them, and over how long? For example, if I'd start to have problems after 10 years I probably don't care, however if I'll have issues within a year that's obviously much more relevant.

Any other advice or suggestions?
I'm well aware of my limitations, and experience of roofing is definitely one of them. I'd welcome any other good ideas (especially ones that aren't too cheap expensive or difficult to achieve) that would give me better levels of shade and shower protection than the existing bamboo matting!

Thank you in advance for your help!

EDIT: Corrected "cheap" to "expensive"

 

[freddiemercurystwin]

I think you'll be fine adding corrugated sheets to the existing rafters, no need for anything else assuming it's been well built ad you use the proper fixings. I daresay there may be the odd leak but with a bit of luck the leak wont drip directly into your G&T.

 

[DaKid]

I think you'll be fine adding corrugated sheets to the existing rafters, no need for anything else assuming it's been well built ad you use the proper fixings. I daresay there may be the odd leak but with a bit of luck the leak wont drip directly into your G&T.

Thank you. I am a bit concerned about sag in hot weather if I don't add purlins ... do you think that would be an issue? I'm loth to add sheets of anything on top of the roof, because of the weight ... it was never really designed for that much extra load, although I do think it can handle roofing sheets (and purlins if I *had* to).

I should say, I'd much prefer not to have to add purlins if I can avoid it!

 

[Dereekoo]

it was never really designed for that much extra load,

How do you know what it was designed for, whats the span, size, grade and spacing of the rafters

 

[Why Not Indeed]

Don't forget about snow loading [I assume it occasionally snows, even in leafy Berkshire].

 

[DaKid]

How do you know what it was designed for, whats the span, size, grade and spacing of the rafters

I designed and built it, so in terms of design, I know it was never intended to have a "proper" roof on it. The rafters themselves should be fine (C24 6x2, 4.5m span, 525mm centres), it's more about the structure.

The dimensions are 4m by 6m, with a 3x3 grid of 4x4 posts supporting it (hidden along the centre of the deck). There are no braces for the rafters though, because it wasn't intended to have a proper roof, so if you push one of the uprights there is a small amount of sway. That said, the posts are approx half a metre deep in the ground, and the decking is built on a structure of 2x8 joists across the width, which are bolted to the posts, with 2x6 beams on top of them, so it's hardly going to fall down.

Don't forget about snow loading [I assume it occasionally snows, even in leafy Berkshire].

It's not snowed properly for about 15 years, and the most we've had in the last five years is a few centimetres, so gonna accept that risk. Thanks for pointing it out though ... it's worth mentioning.

 

[freddiemercurystwin]

I think you'll be fine.