Not sure if right forum but here goes,
Single storey extension is pulling away from the main house, i suspect it hasn't been tied into the main house at all. Is it sufficient to strap it some how to the main building or do i need to underpin? the extension is single skin so would have to be demolishedif i wished to extend above it (which i do not). Builder has told me strapping it would be enough. What type of straps do i need (they have to be right angled as cannot use conventional wall ties now) and how often doi repeat the process ie everyother course.