Dave Plowman wrote:

Roger Mills wrote:

A single pane fully glazed uPVC door isn't very rigid at the corners,
and will lozenge given half a chance.

Aren't they steel framed?

They have steel reinforcement in places, but usually not an entire steel
frame. Maybe you can specify it, maybe they include more reinforcement
above a certain size?

You prevent this by strategic
placement of packing pieces between frame and sealed unit - by what is
called "heeling and toeing". The sealed unit then gives the frame the
necessary rigidity.

Yes, need to get the packing right on any opener, and a door is a big
opener with lots of leverage, if you have e.g. a lower foam core panel
obviously that's much lighter than D/G.
Right. How is the frame normally fixed to the 'wall' (my wood
frame)? Just
screws through it?

Into wood that's what I'd expect, into brick frame anchors are typical,
then foam around the gaps, silicone or PVC trim for appearance.

Basically I'm hoping the better locks and seals will keep out water over
the old wood door with just a single latch. Which flexed a fair bit.

Yes, with the in/out/up/down/shake-it-all-about adjustment of the flag
hinges you get a good seal, though the operation is at first non-obvious.