Bitumen sheets over existing metal corrugated roof? Yeah or nae?

[davebridge32]

We have a lean to that runs the full length of the house as per photo. House is about to be re-rendered so I want to tidy up the appearance of the outhouse roof and stop the 1 or 2 leaks it has. Simplest way by my thinking is to lay new sheeting over the top of the existing. Its structurally sound, can be walked on and is 99% leak free - just looks tired. Bitumen sheets seem the cheapest option. Can they be layed on top of the existing metal sheets? There is no boarding under the current metal sheets so I guess I would need to drill through the existing sheets where the joist are, lay the new sheets and then drive fixings through the drilled holes and into the joists. Sound sensible? Not tackled any roofing before so Im just thinking what seems common sense to me!

 

[Deleted member 174758]

Rather than go through that I think I'd rather strip off the metal and just fix the wood to the existing roof frame (rafters, etc). Drilling through sheet timber material, then a variable gap, then sheet metal, then the joist to get a fix sounds like a PIA to me, especially as your metal roof is more than likely to be fixed down with bolts and curved washers which if it is the case would interfere with laying the sheets flat. Whatever else this is a job for access equipment such as a scaffolding tower, as opposed to trying go work off a ladder