Steel roofing fall

[Diver Fred]

the garage roof is showing it's age. Presently it's mineral felt over felt underlay over boarding set on pitch. there are stones on top of the felt also. The boarding is not in the best of nick but not beyond it's life - well from the underside there is no signs of water damage.
The span is 22ft with a 6in fall.

What I'm considering is to sweep the loose stones off/up and then lay polyester coated roofing sheets over the existing felt.
What I'm concerned about is the fall sufficent for such roofing sheets; especially if I'm unable to obtain sheets of the right lenght.

Thoughts.

 

[chappers]

depends on the type of fixings, for through fixings on profiled sheets the minimum recommended pitch is around 4 degrees or about 1 in 14.
For secret fixings you can go as low as 1 degree(1 in50) which is flatter than your roof, which is about 1 in 40 but as you have already guessed you have to be very careful with end to end laps.

 

[Alex Lynn]

instead of fixing corrugated sheets onto the roof, you could overlay with a single ply membrane, I use Koster TPO with a fleecebacking for these jobs when overlaying old roof coverings. in your circumstance, you could mechanically fix the membrane to the roof deck and hot air weld over the fixings - watertight for minimum 25 years! A fairly easy detail with no future problems.