I'm looking at putting a Aluminium Window and Sliding door into an existing single skin brick extension. The room is a lean-to style tacked onto the back of the house, but it was built with just single brick (no timber frame). The rafters sit on a wooden lintel that spans the entire long side of the room and sits on top of the brickwork. I want to replace one old timber window with an aluminium one and another with a sliding door. To make this easier and to add a bit of strength to the room I'm building a stud wall inside the existing brick wall. Finally to the questions:

How much larger should I make the stud wall openings relative to the brick opening to allow for reveals and packers to plumb the window/door?

When ordering windows/door should I specify the size as the size of the brick opening or the stud wall opening?

Cheers,
Paul


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