Attached shed with porous concrete roof

Polo_Cluvie

Hi folks first time posting. I'm looking for some advice. I live in a midterraced house with small block built shed attached. Over the yrs we installed a toilet and sink in there and tiled it. Great as a downstairs loo. The problem is every winter the walls get damp and there's mould. I fed up painting it. I think that the concrete roof built circa 1972 is porous. It's only 10m2. Our neighbours have the very same shed in mirror image in which they have their oil burner installed. I'm trying to figure out the best way to waterproof the roof. I'm thinking I'd only be doing half as neighbours may not want the added expense. Any ideas much appreciated and costs of course. I'm assuming torch on felt is probably going to be the cheapest. I'm not 100% positive the roof is the issue although the outside walls are pebble dashed and are very solid. TIA

ARGINITE

How is the shed ventilated? The moisture could be casued by lack of ventilation and not connected with the roof.

Lumen

A bathroom in an uninsulated, unventilated shed extension is the absolute worst case for condensation.

I doubt it's the roof.

Polo_Cluvie

An open window. There is no shower in there just a sink that's rarely used. It's just a loo for my elderly father. I ended up getting the roof felted. 4mm underlay and 3mm top layer. The walls still appear to be a little damp for why I've no clue

10-10-20

https://www.boards.ie/discussion/comment/119878434#Comment_119878434

If it's block-built from 1972 then it's condensation from a lack of insulation, likely. There is no easy fix here other than to work out how it's constructed and insulate appropriately.