I have damp in a diagonal line that follows a dis-used flue in an upstairs bedroom. The old chimney has been removed, slated -in and is open to the loft space. I suspected a condensation problem so have left the old flue open in the kitchen (covered in plastic shroud) and drilled what is effectively an air brick into the flue in the upstairs bedroom. This has made no difference and the condensation is so bad that water is beading on the inside of the felt in the loft space.
I also now realise that the render on the granite wall in the bedroom will be heavily contaminated with hygroscopic salts so I am planning to completely strip back to granite and re-render with salt inhibitor and tanking solution (probably the Heidi K11 system as this has worked well in other areas of the house).
My question is that I do not want to leave all that condensation pooring into my loft and I want to vent the flue back out through the slates and via a stainless steel pipe and cowl but in the village where I live there is no way stainless steel would be allowed. So does anyone know of any different kind of vents that can be built into or protrude through the natural slate roof?
Also some people have suggested filling the old flue with vermiculite to stop condensation altogether? Does this work and would it not eventually become a big sponge holding damp within the chimney?