Penetration pockets, sometimes referred to as pitch pans or gum
pockets, are best described as square- or rectangular-shaped
sheet-metal boxes. Such objects typically are used to form
weatherproof seals where irregular-shaped penetrations intersect
the field of the roof system. These penetrations can range from
circular to oval to U-shaped and be constructed with materials to
which flashing materials cannot easily adhere.
Currently, the material generally specified for penetration
pockets is a minimum 26-gauge galvanized metal bent a minimum of 4
inches (102 mm) in height with exposed hemmed edges and fabricated
with 4-inch (102-mm) minimum horizontal flanges extending outward
to form a base so the pan can be installed on the roof membrane.
The open metal sides are soldered to form a weatherproof seal. The
pocket then is half-filled with a nonshrink cementitious grout to
form a solid base around the projection and aid in preventing or
blocking the semi-fluid pourable topping from running between the
penetration and deck. The penetration pocket then is topped off
with a pourable sealant compatible with the roof system or
recommended by the roof membrane manufacturer.
Asphaltic and coal-tar-based built-up and modified bitumen roof
system manufacturers stipulate the sheet metal used for penetration
pockets be primed and set in a bed of the appropriate mastic before
flanges are stripped in and flashed. Some single-ply thermoplastic
membrane manufacturers require the use of membrane-coated metal
instead of standard galvanized metal to promote better adhesion of
the material flashing strips to penetration pockets.
Log in or register for FREE access to this article and other Professional Roofing online content.