Re-roofing the shed...metal stitching screws?!

[Frogalot]

This weekend I'm going to re-roof our big garden shed, it's about 5.5x3.5m with a single pitch. An asbestos contractor is coming to remove the leaky old roof. I have shiny new 0.7mm corrugated tin with felt backing ready to put on, 12 pieces so each run is in 2 pieces with a decent overlap. But a few details I'm not sure about...

> I need to cover the shed timbers so that damp anti-condensation backing doesn't rot them - is non-breathable SarkIT ok for this?
> How do metal stitching screws work?!
> I should peel off the anti-condensation backing on the lower edge so water doesn't roll under and soak upwards, what about the upper edge and the overlaps?

Thanks for reading this far!

 

[catlad]

The screws I use are tek screws and have a rubber washer that are self sealing.
At the gutter you can bend a curve to create a drip edge. A small rubber hammer works well but a piece of timber will do.

 

[Frogalot]

I like that idea Just 1cm or so bent down on the ends? I've got tek screws, they just look like they should go into something on the back. Will test on an off cut tomorrow...
Thanks catlad.

 

[catlad]

The Tek screws will only work if they hit timber behind to pull them tight.

 

[Harry Bloomfield]

The Tek screws will only work if they hit timber behind to pull them tight.

..and they go in the bottom of the channel, so they pull flat/ tight against the timber.

 

[Frogalot]

..and they go in the bottom of the channel, so they pull flat/ tight against the timber.

Ahhh, I'd definitely missed that point, thought they'd all be sticking through into nothing...!
Thank you!

 

[Harry Bloomfield]

Ahhh, I'd definitely missed that point, thought they'd all be sticking through into nothing...!
Thank you!

The usual way with corrugated steel and asbestos was that the fixings went through the peaks, with a seal under them. The much lighter metal box is fixed in the bottoms of the channels with special bolts designed for the job, with the seal underneath them.