IDSE

Hi there, I have a similar issue, with the difference that it's for the main house, not extension, for semi-teraced house. Currently there is 300mm to the party wall on one side and 605mm to the end of the wall on the other side. Now, the opening next to the party will be widened (from a small window they are making 3000mm bifold door), but the opening will be starting from 605mm from the party wall line. Will I need windpost at that opening or can I omit it as I am actually adding more buttressing masonry on that side? The house is older, so I believe there is no windpost there currently. Looking forward to hearing your thoughts on the above! Thanks!