Faced with the prospect of spending the next 10 years chasing leaks, I'd suggest GSI rather than DIY.

Unless you're a masochistic Yorkshireman.

Oh, and corrugated PVC looks crap - go for the cellular polycarbonate that is used on conservatory roofs, or you'll end-up sitting under it looking up at the crud that has accumulated in the dips.

British Standards in Construction Materials

Originally Posted by cloudbuster

Faced with the prospect of spending the next 10 years chasing leaks, I'd suggest GSI rather than DIY.

Unless you're a masochistic Yorkshireman.

Oh, and corrugated PVC looks crap - go for the cellular uPVC that is used on conservatory roofs, or you'll end-up sitting under it looking up at the crud that has accumulated in the dips.

If you use that, and you do a good of sealling it down, you may find it gets quite warm under there... maybe good for a 'semi-green' house.

Originally Posted by chocolate_frog

If you use that, and you do a good of sealling it down, you may find it gets quite warm under there... maybe good for a 'semi-green' house.

Good for SHEDding rainwater, though.

Originally Posted by chocolate_frog

If you use that, and you do a good of sealling it down, you may find it gets quite warm under there... maybe good for a 'semi-green' house.

Semi-green house!!………heretic……you should be stoned.

It’s a shed! Now go and stand in the corner and think about what you have said!

Om reflection, I think that's it - the slope running with the passageway, not across it. There were some cosmetic reasons why this was not chosen but on reflection they aren't really valid.

That cellular UPVC stuff is much more expensive, it seems to me. It doesn't matter about it getting hot under there - the main aim is to keep wood dry so if it helped dry it out, so much the better.

Having a flat sheet to butt up against the sides will eliminate having to take a chance on whether your wriggly-plastic meets the edge on an up- or down-turn, and makes it easier to get your flashing (I'm assuming that you want a reasonable seal to the edges) sorted.

I hope it keeps water out better than anything Westlands pushed-out the hangar door.

Don't forget to post pics on completion.

If it's only 4m long why not slope it to one end and run the guttering along there?

Originally Posted by sunami

If it's only 4m long why not slope it to one end and run the guttering along there?

*sound of tumble weed gently blowing by*

It sounds to me like you need to put lead flashing along the edges to waterproof it. You can either use lead flashing whch entails cutting a chase, fitting the flashing into it with wedges and then making good with sealant or you can get some self adhesive plastic flashing Providing the walls are even, that can work. Your guttering would run across the end with the downpipe running into a drain or even just onto the pavement.