Existing roof pitch too low?

[diy_fun_uk]

Some rough measurements for you.

5.4m: Garage length (internal dimension taken)
15cm: Rise

According to online pitch calculators, this equates to roughly 3 degree pitch? The existing roofing is concrete sheets, supported by joists every 85cm. I had hoped to arrange replacement with something like this (leaving existing wooden structure in place), however although designed for lower pitched roofs it still has a minimum of 5 degrees. Would it work if additional supports were introduced between existing joists, or is the pitch too low to allow for sufficient rain runoff?

Onduline - Black Corrugated Bitumen Roof Sheet (2000 x 950mm) (roofingmegastore.co.uk)

Existing sheets are now failing in terms of water ingress, however I want to find a cost effective replacement solution as the garage is only used for storage and I'll likely be moving in a few years so don't need a tier 1 system. Some pics below. Even for the original install, a rise of just 15cm seems very low?

 

[tony1851]

If you propose using Onduline, I'd be inclined to forget it (been there, done that)
After a year or so, the ends turn up at the overlaps.
Absolutely disgusting product.

 

[diy_fun_uk]

If you propose using Onduline, I'd be inclined to forget it (been there, done that)
After a year or so, the ends turn up at the overlaps.
Absolutely disgusting product.

Thanks for the advice. I don't want to go down the route of having the roof paneled and felted or EPDM'd for the reasons given, so if there are decent corrugated sheeting products out there I'd be more inclined to go that route. I suppose it would be a relatively straightforward job for a roofer to increase the pitch slightly and open up my options product wise?

 

[tony1851]

I think you'd be looking at a metal roof - I did ours a couple of years ago and they're easy to fix; not particularly expensive either, but IIRC you need a minimum 7° pitch.
Just google 'sheet metal roofing' - there are a good few suppliers.