01 May 1999
difficult when existing materials are being torn off. Protecting the newly applied membrane from tear-off
debris and construction traffic is critical.
d. Familiarity with the System and Site. Safety is of paramount importance. Occupants must be
protected from fumes by coordinating the shut down of air handling units. Areas where roofing work is
taking place directly overhead must be cordoned off especially if deck repairs are taking place.
Entrances to the building must be protected from falling materials. Underground tanks and the like must
be identified so that heavy vehicles do not overload these areas.
e. Life Expectancy and Costs. It is likely that a re-cover will not last as long as a total tear-off and
replacement. Avoidance of a tear off is cost effective but re-cover is limited by most codes to one or two
layers so eventually total roof replacement must be faced. Costs are greatly affected by ease of access,
whether slope buildup is necessary, and mechanical equipment must be raised for access. Reroofing is
an excellent time to remove obsolete equipment and stacks from the roof.
(1) Protecting the Building. Reroofing invariably means disruption of building operations. For
some sensitive occupancies (e.g., top floor computer rooms, surgical suites, laboratories or telephone
equipment) a total tear off may be an unacceptable risk. In design of such buildings it is prudent to install
a secondary roof membrane and drainage at the deck level. This membrane keeps the building in the dry
in the event of leaks in the primary membrane as well as during roof replacement. It can also serve as a
(2) Deck Replacement. If deck replacement is necessary the operations beneath will require
shut down for safety and leakage reasons. It also may be impossible to maintain HVAC services,
humidity control, and air exchange with the building open.
g. Low-Sloped vs Steep Roofs. The presence of an attic space provides separation of
construction activities from the interior of the building. On steeper slopes scaffolding may be a major
construction item as well as protected access to the building.
11-2. BUILDING ELEMENTS.
a. Slope. The first decision is whether a watershedding or waterproof system is wanted.
b. Low-Sloped Roofs. Recessing internal drains is beneficial.
It may be appropriate to add
crickets to divert water away from curbs and flashings towards drains.
c. Steep Roofs. It is important to give special attention to flashing and valley design. Interior
gutters are a problematic feature, particularly for metal systems.
d. Structural Considerations.
(1) Adding Weight. Addition of new structurals or using a replacement roof that is much heavier
than the previous requires analysis by a structural engineer. Re-cover and reroofing operations add
significant weight to a structure.
(2) Deck Integrity. At the time of reroofing, the existing deck should be carefully examined to
verify that it is capable of receiving a new roofing system. Damaged decking must be replaced or repaired
and loose decking reattached. Tear-off down to the deck permits careful examination of the deck, re-