We have condentsaion and damp around bedroom Bay Window.

How old is the property 2) is it a brick construction You are on a third floor 1) Wood floor 2) Check for air bricks if not install d have air vents from the outer wall to the inner WalL on your level install air circulation should solve the Damp problem 3) Air vent to the bathroom

With out seening the poroperty its hard but i would think its all to do with humidaty and if you can not replase the windows have you tryed some paint like hammerite paint? As for the damp and mould i would advice fitting a P.I.V Positive Input Ventilation (PIV) This Eco Heat is a low energy whole house ventilation system. It uses the Positive Input Ventilation (PIV) principle to cure condensation and improve indoor air quality, creating a healthy living environment. This PIV system is suitable for three storey properties with lofts. It is a cost effective and energy efficient solution to problems condensation and damp. How does PIV works? This Nuaire unit utilises the latest in PIV technology. Fresh, filtered air is drawn into the home at a continuous rate. This encourages the movement of air from inside to outside. To achieve this, the ventilation unit is mounted in the loft space. It then draws air through the filters and inputs it into the property via a diffuser located in the hallway ceiling. Benefits Prevents Mould Growth The Nuaire condensation control positive input unit reduces the humidity levels in the air. This cures condensation and prevents mould growth and other issues with damp.

From the description it sounds like two problems damp and lack of air movement because of the steel window you will have a constant battle with damp and black spore ( mould ) keep area Warm and ventilate wash down every now and then with week bleach solution . Hope this dose the trick kind regards Bob Dean

Internal damp issues, you need cross venting , extra vents , are you drying clothes in the flat , even condensing dryer creates issues , cooking steaming , internal bathroom , washing on internal clothes line , radiator , all create damp issues, so external vents need to be in place to create cross venting , fresh air in , moving damp air out , single pain glass with your metal frames also not good , warm moist air inside meeting cold air from walls and windows creates dampness