corrugated plastic roof

[Stephen]

Hello,

My flat roof (over the car port) has started leaking so I thought it might be better to replace the flat roof with sloping plastic sheeting like this:

also sell a bitumised version, which they claim is better because it is UV resistant. Has anyone used this? Is it worth buying rather than the plastic?

I assumed that I would run some rafters parallel with the sheets but the instructions say that actually I should use purlins perpendicular to the sheets. I am puzzled by this. My way seems easier because I have a wall at each end to attach the timber to. What am I supposed to fix the purlins to?

The instructions are vague about the pitch. It seems you can use anything from 5 degrees upwards. is there an optimum angle?

Do you have any other tips or advice?

Thanks, Stephen.

[Chris J Dixon]

Corrugated sheets are stiff only because of the corrugations.

With purlins as suggested, the sheets will comfortably support themselves. If you run rafters parallel to the sheets, they will tend to sag between them.

Chris

[tonyjeffs]

I just replaced the roof of my car port after 15 years - transparant corrugated plastic sheeting. Pitch about 10 deg, I'd guess. I put the beams parralel with the sheets because I think it looks better, but along with what Chris wrote, I had to put 2" x 1" cross- members in at 2' intervals to stop the boards sagging. So an easier sensible job would be to put them perpendicular in the first place. The plastic lasts 10-15 years before it becomes brittle and prone to crack on impact. It has the advantage of being cheap, easy to install and nice and bright, though. Tony

[Vortex2]

The bitumenised version sold at Wickes is called Onduline. I would use it instead of plastic if only for aesthetic reasons. Also I suspect much longer lasting and "quieter" in the rain (if that's important).

Download the "fixing guide" from here for more info:

gets "soft" in the sun so purlins at 30-45cm really are a necessity.

Beware B&Q sell a similar product called Coroline (AFAIK made by the same people) which is inferior but no cheaper.

[srp]

the plastic I used to do my conservatory ( about 6 years ago ) seems to have some sort of UV filter/ resistance. I used shorter 90 degree bits of plastic to join these B&Q sheets to the wall and the shorter bits have all gone brown and brittle.

Simon