Ground floor rear extension. Pitched roof covered in large tiles with 2 velux roof windows installed in roof span. Rear wall of extension is block and brick, cavity wall with french doors one side, casement window on other. Width of wall between doors and window is currently 815mm. I intend to install a wider casement window, thus reducing the width of wall/pillar between to 300mm... to leave 150mm of overhang for the lintel above the door and 150mm for the wider lintel above the window... the lintels would then (in effect) touch each other.
Having exposed some of the wall around the top left corner of the existing window, I notice that the it has a catnic (or other steel) lintel above it and I presume the french doors will have same. It looks like the standard 6" (150mm overhang has been implemented.
The inside of the extension (kitchen) is a vaulted ceiling so I reckon I can prop the wall plate from inside using strongboys and props (2 probably) to carry the load of the roof.
Does this sound like a plan? Can the 2 lintels touch... leaving 300mm below for the window and doors? Would it be best for me to replace the steel lintel with the same thing, just wider? Or should I opt for a couple of concrete lintels, to support each leaf of the wall separately?
Any tips on retro fitting a catnip with a wider one. Obviously, getting the house weather proof and secure at the end of each day is important so advice on stages of the work would be really useful, i.e. lintel in one day and then the window in the next, followed by making good?
I've only done this before with replacing 2 x 4" concrete lintels on inner and then outer leaves which was easy, so this is a bit more involved.
Thanks for any help.