Installer R Bell Construction who recently completed their first DER #installation at a large domestic property in Surrey. Owner, Roy Bell said: “On other aluminium windows and doors, fitting the gasket and seal can be both cumbersome and fiddly to get an effective, tight seal. But with DER the knock-in pre-gasketed beads make the job quick, easy and accurate. It eliminates gaskets getting overstretched too, which can often happen on other products. After fitting DER, it’s fair to say I won’t be fitting anything else.”