Roofing, Flashings and Chimneys
The primary function of the roof system is to protect against and manage the
weather elements, particularly precipitation, thereby protecting the interior
and structural components of the home. For the purposes of a home inspection,
the roof system consists primarily of the roof coverings, flashings and chimney.
In addition to protecting the interior elements of the home the roof components
should also be designed, in conjunction with the gutters and downspouts, to
direct rainwater and runoff away from the foundation area, to help reduce the
potential for soil erosion, compaction and water entering the basement area.
Because of the important functions this system provides, it's condition should
be assessed regularly, and maintenance provided when and wherever necessary.
Roofing
There are two basic types of roof construction, sloped (also called pitched)
and flat. Most sloped roofs are covered with individual pieces of shingling
material overlapped to prevent water penetration. flat roofs are basically
watertight membranes that should have just enough slope to allow water to run
off. The slope of a roof can be a factor in the life expectancy of the roofing
material. The life expectancy of a roof covering is also dependent upon the type
of material used, the quality of workmanship, exposure to sun and wear from tree
branches, snow/ice and wind. For example, south and west roof faces have a
higher wear factor than north or east exposures, highly reflective shingles tend
to have a longer life expectancy, and cement or slate roofs last much longer
than standard asphalt shingles (and cost a lot more!)
Asphalt shingling is the most common roofing material used in residential
construction in Canada. Other types of covering for sloped roofs include asphalt
roll roofing, concrete or clay tiles, wood shakes and shingles, and slate
shingles. There are also fiberglass shingles, metal shingles and metal sheet
roofing systems.
Flat roofs are built up with layers of molten asphalt and felts, or covered with
a membrane of modified bitumin or asphalt base, or plastics or rubber. Most are
heat-sealed and some are glued.
Flashings
The purpose of flashings is to prevent the entry of water at areas on a roof
where two components join together or intersect (i.e. one roof to another or a
chimney thru a roof). Flashings can be constructed of galvanized steel, tin,
aluminum, copper, lead or lengths of roll-roofing. The choice of flashing
material will be dependent upon the construction of the roof and the material
used for the roof covering.
Flashings will expand and contract, metal in particular, with heat from the sun
and air temperature changes. They are also expected to move and stretch with
typical building shifts. The areas where flashings are required are typically
very vulnerable to water penetration. There is a high risk of water leakage and
wood decay from a damaged, loose or poorly constructed flashing. For all of the
above reasons, regular monitoring and routine maintenance of the flashing areas
is essential to preventing leaks.
Chimneys
The most common materials used in chimney construction are masonry and steel.
Masonry chimneys can be brick, block or stone and are sometimes stuccoed or
parged. Chimneys often have more than one flue. A flue is a separate and
distinct channel for the smoke on the inside of the chimney. In most cases, each
appliance within the house must have a separate flue. In certain cases, two gas
furnaces on the same floor within a house can share a common flue, as can a gas
furnace and a gas hot water heater on the same level. Some wood furnaces are
designed to share a flue with an oil furnace, if at the same floor level.
Some flues are unlined in that there is masonry exposed on the inside of the
flue. Unlined chimney flues are most common in houses built before the Second
World War. These unlined masonry flues have performed reasonably well for
fireplaces and oil-fired furnaces, however most have deteriorated beyond a safe
condition. Gas appliances require a suitable liner.
Flue can be lined with clay tiles or metal liner. For more information about
chimneys and chimney liners, refer to the "Heating" section.
Skylights
Skylights are windows installed into a roof, where the ceiling is vaulted
with the roof, or where a well has been constructed thru the attic area, to
provide a passage from the ceiling to the roof window. Ideally, skylights should
be installed on curbs, projecting at least 6 inches above the roof surface, in
order that proper flashings can be applied. Some skylights are manufactured with
built-in curb and flashing assemblies. Sometimes skylights are installed flush
to the roof. This configuration almost always leads to water penetration at the
joint between the skylight and the roofing material. Frequent monitoring and
regular maintenance of this joint are essential to reducing the incidence of
water penetration.
Considerations
The component of roofs that is most vulnerable to early deterioration is the
area around the flashings (chimneys, plumbing stacks, the intersection of two or
more roofs, skylights, etc.) It is not uncommon for these areas to develop a
leak well before the rest of the roof material has aged significantly. Also,
because these areas are frequently made of metal they can be more susceptible
than the rest of the roof coverings to damage from wind and
expansion/contraction from freeze/thaw cycles. So while flashings may appear
fine on the day of an inspection and the roof may be relatively young in age,
the flashings should be monitored on a regular basis (at least semi-annually) to
detect any changes in condition that may indicate maintenance or repair is
necessary. Leaks left unattended can cause serious damage to other parts of the
roof and structure.
Flat roof technology has been improving and some of the newer methods are
predicted to last longer with fewer problems. However, as a generalization, flat
roofs are more vulnerable to leakage than sloped roofs. The traditional method
of covering flat roofs with built up material does work, but it has a shorted
life expectancy than some of the newer materials and there is an increased
possibility of premature leakage. A primary factor in the life expectancy of a
built-up roof is the workmanship of the installers. Built-up roofs with
excellent workmanship will last up to 15 years, while the work of less skilled
installers may develop problems in 5 years or less. A flat roof that is past
mid-life may develop leaks fairly quickly. Because of this behavior
characteristic we recommend monitoring of flat roofs to detect signs or symptoms
that may indicate imminent failure.
Copyright Gil Strachan - All rights reserved.
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