(Photo: Christin Klose, Deutsche Presse-Agentur)

Window fittings need to be lubricated at least once a year, with all moving parts receiving a drop of oil, experts say.

The window seals also need to be kept clean, according to technical specialists from Germany's Verband Fenster + Fassade, an association for window manufacturers.

Specialist products for these rubber parts can help to keep them soft and maintain proper sealing.

The drainage hole at the bottom of the windows can also be cleaned with a small screwdriver to ensure rainwater drains through.

Even if windows are very dirty, aggressive chemical cleaning agents, blades and scrapers should be avoided. Standard window cleaning agents are usually enough, and in the case of grease and oil, white spirit should do the trick.

The technical specialists recommend using plenty of water on the outside in particular, where grains of sand and dust can become stuck to the glass.

Cleaning windows with a cloth or window rubber without sufficient water can cause scratches. It is also important to rinse off cleaning agents thoroughly when the job is done.

Written by Simone A Mayer for Deutsche Presse-Agentur