Roger Mills wrote:
In an earlier contribution to this discussion,
Stuart Noble wrote:

Yes, it's a c section, but I wonder what the function of the hardwood
frame would be.

The wood - or the legs of an H-section frame - provide bending stiffness.
With a wooden frame, the ally will be flat against the wood, and if the
brickwork is irregular, there will be uneven gaps between the wood and the
brick - which you fill with sealant. If you try to screw the ally straight
to the bricks, chances are that it will bend.

Some of my ally windows have more like an F section, with one leg which goes
*almost* to the brickwork - with the wooden frame going all the way, and
with the otherwise exposed bit of wood being covered by sealant - so they're
zero maintenance.

Continuing this (I don't move fast), this is a cross section of the aly
frame.



When screwing this to the wooden frame I assume it needs to be a tight
fit but, with just two 1mm legs in contact with the wood, it would need
to be mighty accurate to avoid leaks. Am I missing a gasket of some
kind, or is it just a silicone job?