17. Installation – prefabricated chimneys (b) The adjustable roof support offers another way to support the chimney. It gimbles to the angle of the roof and can deal with any pitch. XXA flashing or "slate-piece" provides protection against the weather entering at the point of exit. Typically it is made from a malleable material so that it can be cut and shaped to underlap slates above and overlap the slates below. It is sealed at the top with a bead of silicone mastic which is protected from the weather by a storm collar sealed with further mastic. In most cases a raincap is used as a terminal but other alternatives may be available to suit particular needs. XXThis is the simplest, cheapest and most efficient configuration you can have and you should not consider more complicated alternatives unless they are forced upon you! XXIn approving the installation of a sectional chimney, Building Control will seek confirmation that you have complied with the manufacturer's instructions throughout. These notes are intended only to explain the principles used by one or two of the more popular chimney manufacturers.