On Wed, 10 Mar 2010 11:17:27 -0000, David WE Roberts wrote:

Looking at the roof design (I have looked back through previous useful
threads).

I am considering 6" (150mm) * 3" (75mm) at 600mm spacing.
The span is about 3.5m front to back and about 7.8m side to side.
The proposed roofing is metal sheet.
I am assuming the joists will span the short (front to back) span.

The issue now is how to engineer the slope (I have read that 1/2" per foot
is adequate so a difference of 6" front to back should be O.K.).

I can see some obvious ways:

(1) Front and back wall level. Hang the lower end of the joist flush with
the wall plate and rest the base of the high end of the joist on the wall
plate. This will require the low end cutting at an angle to sit properly in
the joist hanger and the high end notching to sit onto the wall plate.
Sloping ceiling.

(2) Front wall one block higher than rear. Hang both ends from joist
hangers. Both ends will need cutting at an angle to fit the joist hangers.
Sloping ceiling.

(3) Front and back wall level. Hand the main joist parallel from front and
back wall. Fit a profiled piece of timber above the joist. Simple hanging,
no angles cut, less lateral force on the walls (not that there should be
much anyway). Flat ceiling. Downside (if any) seems to be the odd shaped
roof void which will give a lot of air space above the insulation at the
higher end.

What dos the team think?

TIA

Dave R

One thing to watch ... I used galvanised steel sheet for covering my
shallow angle garage roof (existing wooden roof) and got water coming in -
it turned out that at shallow angles, the water can run back under the
lower edge of the sheet and far enough uphill to get into the structure. I
solved the problem by screwing a 3/8" piece of angle 3/4" back from the
edge as drip-edge. Luckily there was no problem with the high part of the
profile (despite it being flat on top) and so I could just run the angle
straight across the bottom.

SteveW