01 May 1999
covering does not. Pull-out capacity of fasteners should be determined per TI 809-29 Paragraph 7.k or
SPRI recommended practice.
(3) Upgrading. Review of ANSI/ASCE 7-95 may indicate that strengthening of the system is
required to meet new load requirements. Consider adding new roof- or overflow-drains.
(4) Rooftop Equipment. Assess whether rooftop equipment can be relocated or removed.
Consider raising the height of curbs to accommodate thicker insulation or changes in slope.
e. Expansion and Seismic Joints.
(1) Roof Joints. Are existing joints adequate? Are more needed? Consider adding new joints
where differential movement or stress accumulation has been noted.
(2) Fire Stop at Joints. If a steep roof conversion is done which bridges an existing structural
expansion joint and now places it within the newly created attic space, it may be necessary to convert the
joint into a fire stop. Refer to Factory Mutual Loss Prevention Data Sheet 1-31 for details.
f. Re-entrant Corners. Examination of the existing system will help establish whether area dividers
are needed at these locations.
g. Roof Access. If access has been inadequate, this is the time to improve it. In addition, attic
spaces created in slope roof conversions may require access if the attic height is 760 mm (30 inches) or
h. Roof Venting. Ventilation of attics and cathedral ceilings is often appropriate to control building
moisture. When reroofing steep systems the attic space must be examined for evidence of condensation
problems as well as roof leakage. Continuous intakes along eaves in combination with soffit vents are
quite effective. Most compact low-slope membrane roofs should not be ventilated.
i. Roof Decks. When the existing deck is to be reused it should be examined for conditions. Refer
to Structural Safety Issues in Reroofing in ORNL CONF-9405206.
j. Underlayment. In steep roof designs such as with tile and slate, the underlayment may be the
first element to fail. Replacement along with deck repair may permit reuse of the tiles or slates. In
membrane re-cover, use re-cover boards to separate the new membrane system from the old.
k. Vapor Retarders. Examination of the existing system may be the best way to decide what is
needed when reroofing. Existing vapor retarders may be poorly attached, may not have edges sealed, or
may be full of holes. Consider installation of new retarder either at deck level or on top of a new thin layer
of rigid underlayment board.
l. Thermal Insulation and Heat Flow. Most existing buildings are underinsulated by today's energy
(1) Reinsulating of Attics. For steep roofing systems with an attic space insulation can be
superimposed over existing insulation. The new materials should be unfaced to avoid creating a second
vapor retarder. However, installing a vapor-permeable air barrier may be beneficial. Care should be
taken to keep the insulation from blocking attic ventilation airways at eaves.
(2) Separator Board of Membrane Roofing. For low-slope roofing systems, if additional thermal
resistance is not needed, a thin re-cover board may be used to separate the old roof system from the