Plastic corrugated roofing

No, the corrugations will prevent this

Just tuck the end under the edge of the shed roof

Nope, the extension is going from the end of the shed so although I can tuck under at one edge the rest of the extension will be over fresh air and a slope from back to front.

I think you can get a moulding that is meant to seal against a wall plate. adapting that will get you to a straight line to which you can add something to give a drip edge.

No, but you could roughen the surface and run a bead of roof sealant along there.

Bill

You could always use a roll of flashing tape to form a peak along the join between the two sheets.

Removes a little bit of light but it should make it water tight and also should be fairly mouldable into the corrugations.

Cheers

Dave R

I have sealed a folded ridge sheet to box section roofing using expanding foam.

I suppose *light* lead flashing might form into the gulleys slightly but I don't think you could stop wind blowing snow and light rain up the gaps on anything other than a steep pitch roof.

Trimming the excess foam with a knife exposes significant voids.

I'm having trouble imagining where this extension bit of roof is going. Is it an extension away from the side of the shed at shed roof eaves level or an extension from a gable end of the of the sheds pitched roof (assuming it has a pitched roof)?

You can certainly get moulded ridge pieces and I thing moulded to flat bits as well. The latter would be used to butt against a wall with the roofing sheet underneath and flashing into the wall and over the top edge along the top of the flat bit.

Should be able to form lead to the corrugations without too much trouble, but probably best to do in situ which might not be easy as the roofing sheet isn't load bearing...

Domestic "foam in a can" I agreed more voids than swiss cheese. You can get foams that are much more uniform and aimed at the commercial/trade market, the low expansion ones?

Why is it that this stuff lasts for maybe 6 years then suddenly goes milky and brittle? One would have thought if it were the UV it would happen gradually.

This Novolux will self destruct in 6 years, thank you for using it..

Brian