Long-term testing of windows Experience from window replacement The windows in one of SP's buildings were replaced at the end of 1994/beginning of 1995. When the proposal to replace the windows was first raised, it was suggested that it could provide an opportunity for long term testing of P-marked and type-approved windows. The facade faces south east, and is very exposed to weather and wind. The objective of the project was to examine the condition of the old windows and to investigate the durability of the new ones. As far as the new windows were concerned, there was particular interest in investigating different designs, materials and combinations of materials in frames and casements. The old windows had wooden frames and casements, and were in very poor condition as a result of neglected maintenance. The moisture ratio in the bottom members of the casements was particularly high, and many of the casements were badly attacked by rot. On the other hand, only a few windows were suffering from rot in the bottom members of the frames. The new windows have been supplied by ten different manufacturers, and together comprise 13 different designs. All are of triple glazed type. The frame and casement materials are wood, wood with an external aluminium cladding, plastic and aluminium. The windows have now been inspected three times: in 1997, 1999 and 2000. The results indicate that the condition of the surface treatment seems to be very important for the moisture ratio in the windows, as is also the design. In particular, fittings such as storm hooks should be avoided, as they have a considerable effect on the durability of the windows. The wooden windows showed high moisture ratios at their last inspection. The external finish on them has deteriorated with time, so that there are now cracks and flaking of the paint that explains the high moisture ratio. Those with aluminium cladding, on the other hand, were dryer, which shows that the cladding has been correctly fitted. Plastic and aluminium windows showed no visible signs of colour or shape change at the last inspection. This experience of long term testing will result in changes to the P-marking rules for windows. It will also be fed back to the manufacturers in order to enable them to improve the performance and durability of their products.