Hi guys i posted thread while back about damp upstairs chimney breast. Took advice and got stack rebuilt was real happy with stack but damp got worse. Roofer came back put wider lead painted fiber glass on top and coated sides and put better breathable membrane down. 2 weeks later still damp. Chimney sweep said possible problem is rain is getting in between pot and chimney liner so recomended a suspension cowl that covers the gap. Roofer said we may need ventilation caps as old 2nd chimney breast is blanked off.
Neighbour has same problem in same place didnt have the damp until new stack was built but i did.