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Solution:  Perimeter roof drain systems are preferred. As a general rule, all
buildings having a width of 100 feet or less should use perimeter roof
drains.  For buildings that use interior roof drains, consideration should be
given to provide the following:
Accessibility for future maintenance.
In cold climates insulating roof drain piping above the ceiling.
Securing of roof drain piping above the ceiling adequately to prevent
leaks caused by vibration during routing-out.
CASE All - Roofing and Waterproofing, C. B. Key
Roofing Flashing Failures.
Collection of Facts:  Experience has shown that the majority of leaks in
roofing systems occur at flashings.  If the problem is not detected and
repaired soon enough, it could result in serious and costly damage to the roof
assembly, building structure, and interior finishes and contents.  The
inconvenience and frustrations of building users are transformed into low
morale and lost productivity of the organization.  Although the roofing
generally represents only 2% of the total building cost, over 50% of all
design and construction contract litigation results from roofing problems.
There is nothing more embarrassing to a designer, contractor, or building
owner than to have a roof leak in what otherwise appears to be a well designed
and constructed building, representing a tremendous capital investment.  Then
there is repair or replacement cost for the roofing system and related
damages.  The cost of roofing replacement alone can run from $250 to $500 a
square (100 sq.ft.) depending on the type of roofing and complexity of the
job.  The Lessons Learned are that flashings fail generally for one of two
reasons: (1) failure to incorporate provisions to accommodate differential
movement resulting from thermal expansion and contraction or deflection; and
(2) failure to incorporate the most maintenance free design concepts.
Preventative maintenance is very seldom accomplished and is generally only
provided in a crisis when the roof leak is visible and disturbing within the
Solution:  It is the design philosophy of the Naval Facilities Engineering
Command to incorporate features in flashing details that will accommodate
differential movement and provide the most maintenance free design concepts.
Specific examples are provided as follows:
Minimize the number of penetrations through the roof by grouping
pipes and conduits into fewer strategic locations. See attachment 1.
Assure that penetrations do not occur at low points of the roof.
Do not use pitch pockets.  See attachments 2 and 3. Pitch pockets
require frequent inspection and maintenance to maintain a waterproof
seal.  Use flashing collars with umbrella flashings. See attachment

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