Cedar shingles/shakes

[ibisti]

I was wondering if anyone has had any experience with these? I have a large shed/garage that needs to be either re felted or as another option I thought I might use cedar shingles. If you have used them what is the process of fitting them? I have seen that you overlap on each row but do you need to fit anything underneath them? I was going to lay them over the existing felt that is past its best, but still mostly water tight.

[ibisti]

Its about 20deg pitch I think

[ibisti]

Why do you say 20 deg is not recommended? Most shingle retailers seem to quote for pitches of 14 to 19deg and then over 20deg. Then the spacing is altered to cope.