Expansion joints and/or control joints;
Structural adequacy or load-bearing capacity in
conformance to current design criteria;
Deterioration of parapet walls and/or adjacent
Interior Space Conditions.
Psychrometric factors to be
considered include the following:
Building occupancy (current and proposed);
Existing building heating, ventilating, air
conditioning, and humidification systems;
Maximum hour location of dew point within the roof
Vapor retarder requirements. Be aware of vapor
pressure direction in humid climates which is usually downward.
Design Considerations. The most basic design decision
in reroofing is to either recover or replace. Always use
nondestructive testing before designing. A leaking roof which is
classified as a premature failure must be evaluated for potential
contributions to the failure (refer to par. 10.3). Never recover
even a partially water-saturated insulation-membrane system. If
the roof has been recovered once, a second recovering is not
allowed. Design options are either recovery or replacement.
Consider all options for best choice.
Drainage. Adding slope will eliminate the major cause
of premature roofing failure. However, on some existing low
slope decks it is costly or impractical to create a 1/2-inch per
foot (4 percent) slope with tapered insulation. Where existing
low slope or near level roofs have failed due to old age and not