Designing for Building Maintainability - Effective Building Maintenance: Protection of Capital Assets - page 144

and solvents around kitchen exhaust fans, coal tar is susceptible to cold
weather cracking (bitumen is not), and more complex details are re-
quired for roof penetrations and at parapets and roof curbs.
With any type of low slope roof, the following elements must be
considered:
1. The use of a non-hygroscopic insulation is highly recommended,
since this type of insulation, even if wet, will retain most of its
thermal properties. The two most common non-hygroscopic insu-
lation materials are cellular glass (expensive, but well worth it if
significant roof traffic is anticipated) or polyisocyanurate. If roof-
ing insulation gets wet, and if it is the type of insulation whose
thermal performance degrades with moisture content (fiberglass,
mineral wool, etc.), conditions are such that condensation in or on
the bottom of the roof can occur. This will allow both mold growth
and condensation that can drip onto ceiling structure, tiles, ducts,
and pipes below to contribute to mold growth there.
2. Consider locating rooftop equipment inside penthouses. If equip-
ment is located outside on the roof, a platform or continuous roof
curb is required. Platforms should be structural steel frames above
the roof surface. Pipe columns through the deck to the structural
frame are the simplest to flash. Clearancebelowtheequipmentshould
besuficienttoallowforrooingserviceandrepairs . Structural roof
penetrations must be sealed, flashed, and counter-flashed to pre-
vent water intrusion. Cubs must be full perimeter type, designed
for the type of roof. Curbs must extend a minimum of 8” above the
roof surface or above the height of any emergency overflow pipe
or scupper, whichever is higher. Curbs must be fully flashed and
have detachable secondary counter-flashing around all four sides.
Provide walk pads to and around any equipment requiring
routine service or inspection to protect the roofing membrane.
Piping and ductwork routed across the roof must be support-
ed from engineered roof rails with the roof membrane extending
up under a metal counter-flashing. Rails must extend a minimum
of 8” above the roof surface or above the height of any emergency
overflow pipe or scupper, whichever is higher.
3. A vapor retarder is a low slope roof component designed to restrict