I've two last major areas to details for air tightness and insulation - this post relates to one of these - a single rear Oriel Window, an architectural feature that juts out from the rear of the building and is finished externally with a metal standing seam. The plan agreed was to create a 20mm lip of metal for the window to sit against. I was right about to commence work when I noticed dampness and beads of moisture and sure enough despite the window being surrounded by a later of insulation,
