Corrugated Bitumen roofing sheets

sickparrot

The house I'm moving to has a garage which has black corrugated bitumen roofing. It wasn't installed properly so it has sagged in places and lets water in.

Obviously the whole roof wants stripping off and the damaged sheets replacing (or can they be 'melted' back to shape?), so my question is, do I put lots of extra battens in to hold them up, or put a sheets of plywood or something on the existing battens and then the roofing on top?

Anyone who has used this stuff before have an opinion?

Thanks, Ady

Kiran

I've not personally ever used the stuff, but if its sagging it sounds like your spans are too long. Have you got anymore details eg direction the sheets span, if they are just spanning between the walls of if there are any other method of support at present? If it were me, I'd be tempted to have one timber either end of the corrugated sheet (shared fixing point for the sheets either side) and one in the middle. Thats the typical construction you would see on a car port sheeted roof etc.

In my opinion that wouldn't be overkill, but opinions vary

sickparrot

Currently there's a batten about every 2 feet, but according to the spec's for the sheeting they should be much closer together.

These are them:

http://www.screwfix.com/sfd/i/cat/pdfs/10/p4765210.pdf

For shallow pitch roof it says 'decking or close boarding' (the roof goes from front to back, not middle to side).

The guy who sold us the house told us that this was what the problem was, but what I'm asking basically is:

a) can I rescue the existing sheets, say by laying them flat and heating them up with a fan heater, or once they are warped is that it.

b) can I get away with a layer of plywood or OSB over the existing battens rather than fitting loads more.

thehairybuilder

If these are the sheets I`m thinking of , 2000x900mm approx , then I`d personally renew them . I can`t open your link but you can see the sheets here
http://www.onduline.com/anglais/onduline.php
I`m not convinced that they can be `unbent` but these only cost about £8 each + VAT from any decent builders merchants.
I don`t think you want to be laying ply or osb with these sheets as I feel the bitumen sheets are meant to breath and the boards would interere with this process .
Renew them with extra purlins for support and you`ll be fine I think

ormus

theres no reason why you cant use the OSB method. maybe cheaper than the other options.
as the bitumen sheets are so cheap its not worth trying to recycle them.

Mr_Warren_2

Relax, you can use flat sheets under the corrugated sheets. i transformed a flat roof of our garage that was in a bad state into a good looking 2 slopes new roof using 4"x4" timbers (went a bit heavy on those....), 15mm marine plywood nailed on it and the Wickes bituminous sheets nailed as per instructions. The sheets will breath as the corrugated only lies on the ply on its corrugations. The very detailed instructions offered by Wickes are quite clear on that, battens or sheet ply will do the job very well. Good luck.