The width of the window needs to suit brick size so the purps are constant width. In the “good old days” bricks were standard size, made in UK and windows were built in with width and height to suit standard brick size. Not so simple now with imported bricks.
I had a problem with my complete new build, finished about four years ago. Engineering bricks were standard 215mm long whilst the facing bricks I chose were 210mm. Only realised the problem when bricklayer started by staggering the purps as normal and purps were 15mm, looked terrible. Then a case of working out number of bricks per wall for the new size of brick with 10mm joints. Main issue were the doorways, getting the correct width so brick courses would be correct above the door, particularly the wide bifold doors, could not go by bricks below DPC as normal. Of course the purps between facing and engineering bricks do not line up. No one notices and not a structural issue, these courses are effectively de bonded by the DPM.
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