Pitched felt roof

[ntl142]

My garage has a pitched roof covered with felt. The felt lengths are laid over the pitch of the roof, rather than running along the length of the roof. It leaks, but only on one aspect of the roof. The north facing side is absolutely fine, whereas the sunny side leaks. The leaks are where the sheets have pulled apart at the seams, and where nail holes through the felt have been elongated. I think this is due to expansion/contraction of the wooden roof and/or the felt itself. I don't know if the felt is laid dry or is bonded to the wood. The side door jams when it's hot, but closes freely in the cold, so there is definitely some building movement in hot weather.

I'd like to avoid it happening again, and have a few ideas I'd like suggestions about please.
1. If I lay the felt along the length of the roof then there won't be any vertical joints that can leak in the future. However, that stretching of the felt in the sun will now all be on one length of felt. Is that better?
2. Any recommendation on which orientation to lay the felt? And assuming I lay it on a sunny day, should I lay it taught, or a bit loose?
3. Should I strip the existing felt and lay the new stuff onto the existing boards, or leave the existing felt in place? I'm not sure if bonding the new felt to the underlying wood will make the expansion/contraction issue better or worse.

 

[oldbutnotdead]

Are we talking proper pitched felt here (complete with blowlamp and tar bucket) or shed felt?

Either way if you run the stuff lengthways (ie parallel with the ridge) with plenty of overlap on the joins (for shed felt anyway, not sure about the hot stuff) then you'll be in with a shout.
Shed felt again if you lay it on a sunny day, leave it a bit slack- not baggy. The stuff is slightly viscous anyway.
Shed felt- you need to get all the old nails out otherwise they'll just poke through & wreck your new cover. Pitched felt- how well bonded is the old stuff?