We have 4†joists which are not at even spacings and not all completely parallel, however the trays were easy to use and by simply scoring and folding the trays. Also it was possible to position them at the correct depth to provide support for the 150mm of Rockwool insulation used. I tacked them at the required depth by using a light duty domestic staple gun with 13/4-10 staples. For added security is then used screws and penny washers through the trays into the sides of the joists (see photo). The insulation was then cut to size and simply laid in the tray and the floor replaced. The trays allow the insulation to lie at the correct depth which allows the benefit of the full U value to be obtained, as there is no over-compression of the wool.
