A penetration is any hole cut in a roof or wall cladding to accommodate projections such as pipes, ducts, chimneys, roof lights doors and windows. This section focusses on roof penetrations only. The type of penetration design is determined by:. A copy of this may be obtained by contacting info roofingassn. Terminating a sheet above and below a penetration creates an end span situation and sheet support and fastener patterns should be checked accordingly, or additional support must be provided. Ideally this should be in position before the roof cladding is fixed; alternatively, the supporting framework should be in position before cutting a hole in the cladding.
Roofing Detail: Pipe Penetration with Pre-Formed Flashing Collar | | Building Enclosure
Flashing refers to thin pieces of impervious material installed to prevent the passage of water into a structure from a joint or as part of a weather resistant barrier system. In modern buildings, flashing is intended to decrease water penetration at objects such as chimneys , vent pipes, walls, windows and door openings to make buildings more durable and to reduce indoor mold problems. Metal flashing materials include lead , aluminium , copper ,  stainless steel , zinc alloy , and other materials. The origin of the term flash and flashing are uncertain,  but may come from the Middle English verb flasshen , 'to sprinkle, splash', related to flask.
Under flashings drain at the plane of the roof pan. Overflashings drain at the plane of the rib of the roof. These are also known as back flashings. Tapered flashings that drain at the plane of the roof pan at the top, and over the ribs at the bottom.
Gravity is the driving force behind drainage. In general, the sooner water is directed out the better. Sooner, may not always be practical—such as at window openings where draining a window into a drainage space behind a cladding is often more practical than draining them to the exterior face of the cladding.