Re-Felting A Shed Roof ......

[Gizmonster]

Roof getting a bit tatty now - I recently had to stick a piece back on, that blew off with the high winds (that seems like aaaaages ago now with all this recent warm weather).
The shed itself is around 10 years old and is in quite good condition, as we regularly repaint it.

Anyway - on to my question:
I want to re-felt the whole roof and I'm wondering is there any reason why I couldn't simply nail some new felt on top of the existing felt??
I would like to keep the existing felt, to act as an extra layer of protection, but am I missing something obvious as to why I shouldn't do??
The felt is a bit tatty, but is still fairly waterproof and I'll be simply putting extra felt on top, held in place with roofing clout nails.
I really don't want the hassle of having to strip the roof; but I will if I have to :(
Any advice please??

[woofgang]

I have just had my old shed taken down because the floor was rotten....said to the bloke it was a pity because the rest of the shed looked sound....and it really did from the inside. He called me out to see what was under the roofing felt. The roof wood seen from outside was very rotten indeed!

[The Builder]

I've just had the same problem with my shed, Giz. I covered it in this .........

https://www.cladco.co.uk/products/box-profile-341000-sheets-roofing-and-cladding

"Onduline" is an alternative (available at Wickes and others.)