"David WE Roberts" wrote in message
...
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
What will it be? Shed or room?
If you intend to fit a ceiling, then (3) is correct way.
Fall should be 1 in 60 or greater. The "pofiled pieces of timber" are called
firring, nailed to top of joists.
If fall is in same direction as joists, their shape is a narrow
triangle/taper, no less than 13mm thick at thin end.
If fall is at right angles to joists, their shape is parallell (each piece)
but decreasing in thickness from top of slope to bottom.
Takes some thought and calculation. Remember measure twice cut once!!
You will need to consider direction of joists and covering together, it has
to be fixed into joists.