Pilkington EnergiKare Double Glazing can save a detatched house with single glazed windows upto £14440 over a 20 year Period. Visit Pilkington Energy Kare . Double Glazing with energy costs soaring at 40% in the next year is probable the best investment in home improvements you can make. For cheap double glazing you could buy diy windows. Make sure you replace windows with at least a (C) Energy Rated Window. Posted by Double glazing guide.