CEMP-ET
TI 809-53
01 May 1999
new. This might be rigid glass fiber, perlite, or wood fiber board mechanically attached or mopped to an
old bituminous roof system.
(3) Upgrading Thermal Insulation for Low-Slope Roofing. If additional thermal insulation is
needed rigid foam plastic insulations are highly efficient. Compatibility with the new roof system is of
primary concern.
(4) PMR Conversion. It may be feasible to convert a conventional low-slope roof to a protected
membrane by adding extruded polystyrene foam insulation (XEPS), a filter fabric, and ballast on top of
the existing system. A structural analysis is required if dead loads will increase. Lightweight
insulation/paver composites are available to reduce the amount of dead load added.
m. Membranes. For low-slope systems, compatibility may be an important design factor. For
example, if existing walls and penetrations are contaminated with bitumen it may be simpler to use a
bituminous re-cover rather than to install separators to keep the incompatible membrane and flashing
materials apart. Membrane choice may also be determined by the nature of the problems with the roof
system currently being replaced.
n. Penetrations.
(1) Upgrading Roof Details. Reroofing is an excellent time to replace pitch pockets and other
high maintenance items with more durable details such as curbs with removable, watershedding covers.
The NRCA construction details provide examples.
(2) Maintaining Ventilation. When a steep roof conversion is done, existing roof vents must be
extended through the new roof system.
o. Historical Roof Restoration. CEGS 02226 covers the requirements for removal and salvage of
historic building materials. Often it is appropriate to carefully remove and reuse terra cotta, clay tile trim,
cast architectural ornaments, slate tiles, clay tiles, gutters, leaders, and downspouts. Replacement
materials can be expensive and difficult to obtain.
p. Aesthetics. Reroofing affords an opportunity to maintain or upgrade roof appearance. This EI
has touched on the many roof choices available to the designer. Examination of the existing system may
suggest secondary problems such as wind scour, chemical attack, corrosion or the like that should also
be resolved.
q. Gaps, Flashings, Joints, and Sealants. Reroofing may solve problems caused by failure or
inappropriate use of these elements.
r. Drainage, Valley and Intersection Details. Reroofing is an excellent time to improve on these
critical elements by adding crickets or saddles.
11-3.
DESIGN DETAILS AND ALERTS.
a. Assessment.
Reroofing and re-cover require a careful analysis of existing conditions.
Assessments should include:
(1) Roof Deck
(a) Steel: Rusting? Differential deflection at side or end laps? Excessive deformation?
Sound welds?
11-5
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