Once the condition of the roofing material has been determined,
the related features and support systems should be examined on
the exterior and on the interior of the roof.
- The gutters and downspouts need periodic cleaning and
maintenance since a variety of debris fill them, causing water
to back up and seep under roofing units.
- Water will eventually cause fasteners, sheathing, and roofing
structure to deteriorate.
- During winter, the daily freeze-thaw cycles can cause ice
floes to develop under the roof surface. The pressure from these
ice floes will dislodge the roofing material, especially slates,
shingles, or tiles. Moreover, the buildup of ice dams above
the gutters can trap enough moisture to rot the sheathing or
the structural members.
Many large public buildings have built-in gutters set
within the perimeter of the roof. The downspouts for these gutters
may run within the walls of the building, or drainage may be through
the roof surface or through a parapet to exterior downspouts.
These systems can be effective if properly maintained; however,
if the roof slope is inadequate for good runoff, or if the traps
are allowed to clog, rainwater will form pools on the roof surface.
- Interior downspouts can collect debris and thus back up,
perhaps leaking water into the surrounding walls.
- Exterior downspouts may fill with water, which in cold weather
may freeze and crack the pipes. Conduits from the builtin gutter
to the exterior downspout may also leak water into the surrounding
roof structure or walls.
Failure of the flashing system is usually a major cause
of roof deterioration. Flashing should be carefully inspected
for failure caused by either poor workmanship, thermal stress,
or metal deterioration (both of flashing material itself and of
the fasteners). With many roofing materials, the replacement of
flashing on an existing roof is a major operation, which may require
taking up large sections of the roof surface. Therefore, the installation
of top quality flashing material on a new or replaced roof should
be a primary consideration. Remember, some roofing and flashing
materials are not compatible.
Roof fasteners and clips should also be made of a material compatible
with all other materials used, or coated to prevent rust. For
example, the tannic acid in oak will corrode iron nails.
Some roofs such as slate and sheet metals may fail if nailed too
If the roof structure appears sound and nothing indicates recent
movement, the area to be examined most closely is the roof substrate
the sheathing or the battens. The danger spots would be
near the roof plates, under any exterior patches, at the intersections
of the roof planes, or at vertical surfaces such as dormers. Water
penetration, indicating a breach in the roofing surface or flashing,
should be readily apparent, usually as a damp spot or stain. Probing
with a small pen knife may reveal any rot which may indicate previously
undetected damage to the roofing membrane. Insect infestation
evident by small exit holes and frass (a sawdust-like debris)
should also be noted.
Condensation on the underside of the roofing is undesirable and
indicates improper ventilation. Moisture will have an adverse
effect on any roofing material; a good roof stays dry inside and