Treat the rear addition as a chain of junctions
At the back of a terraced property, roof edges, walls, windows, doors, thresholds and paving meet within a small area. A stain or swollen skirting inside may therefore have several possible sources. Photograph the outside and inside in matching positions and note the weather or activity that precedes the symptom. Check whether the issue appears after rain, cooking, bathing or appliance use. A dated log over several days can separate a weather event from a waste connection or condensation pattern. Include whether windows were open, extraction was running and an appliance cycle had just finished. Do not begin with paint. The useful first decision is whether an accessible seal, fitting or minor component is at fault, or whether roofing, drainage, concealed plumbing or building fabric needs specialist investigation. This evidence can prevent unrelated parts being replaced merely because they sit close to the mark.

