On Tue, 26 Feb 2013 02:23:04 -0800 (PST), harry wrote:

I'm considering building a wooden frame for a felted apex roof to put
over my leaking concrete flat-roof.

All you need to decide is what tiles you are using (hence weight/sq
metre) and they will tell you what distance to put them apart.

Read what is written...

I'm wondering why this has to be an apex roof, what's wrong with a "flat"
roof constructed with a decent fall and covered with GRP or even felt as
the OP wants to use felt for some reason. Felt will fail on an apex roof
just as well as it will fail on a flat roof...

Be a lot simpler and easier to build a flat roof than an apex one. Joists
lifted a inch or so above the existing roof, firing pieces attached to
top, or different sized spaces underneath to get the fall, covered in 18
mm OSB3 and Bob is your fathers brother.

--
Cheers
Dave.