Low Slope Roofing
Built-Up Roofing
Built-up roofing, sometimes referred to as ("tar and gravel") was
introduced during the 1840s and built-up roofing remains the predominant
system installed on low-slope ("flat") roofs.
A built-up roof system consists of multiple plies of reinforcing
material (organic felts, fiberglass mats or polyester), inter-ply layers
of bitumen (asphalt or coal tar) and a finish surfacing, such as gravel
or decorative rock, mineral surface cap sheets, or coatings. Owing to
energy concerns, many built-up systems today incorporate a rigid board
insulation as well.
The repetitiveness of a built-up roofing system -- its layer upon layer
nature -- provides both flexibility and durability. The number of plies
and the materials used for surfacing can be varied to adapt the system
to virtually any environmental or aesthetic concerns. For the same
reason, a built-up roof is more forgiving of abuse after application
than are many other roofing systems.
Modified Bitumens
Modified Bitumens were developed in Europe during the 1960s and have
been in use in the United States since the mid-1970s. The idea was to
improve upon the natural properties of bitumens by modifying them during
the manufacturing process. Typically, this means adding either plastic
or rubber.
When Atatic Polypropylene (APP) is blended into asphalt it makes it more
flexible and increases its resistance to ultraviolet radiation. Some APP
modified bitumen materials have granules embedded in the top surface for
further UV protection and to achieve a fire rating.
The other major modifier for bitumen is Styrene Butadiene Styrene (SBS),
a rubber-like material which improves the ability of sheets to elongate
and recover. SBS sheets are generally mopped down with hot asphalt or
cold adhesive, but some can be torch-applied. Unlike APP modifieds, SBS
is susceptible to damage from long-term exposure to ultraviolet
radiation, so surfacings are necessary to protect them.
Because they are so flexible, modified bitumens are commonly used as
flashing materials in built-up roofing systems.
Cold-Process Roofing
An alternative to traditional built-up roofing, cold process roofing
gets its name from the simple fact that hot asphalt is not utilized. In
place of hot asphalt, "cold" asphalt emulsions or adhesives are applied
between polyester mats or fiberglass base sheets.
A surfacing, typically a ceramic granule surface or rock, is then
usually applied over the membrane to provide protection from ultraviolet
radiation and to achieve a fire rating.
Today, many of the manufacturers of built-up roof systems carry a
product line and specifications designed for cold process applications.
It is a widely approved and acceptable roof system found in today's
architectural designs.
Single-Ply Roof Membranes
This class of low-slope roofing materials encompasses a variety of
products which share the common characteristic of being designed to be
installed in a single layer. Single ply materials are also highly
flexible, which is why they are sometimes referred to as "flexible
membrane systems".
There are two main types of single ply product: thermosets such as EPDM,
CSPE and Neoprene are synthetic rubbers; thermoplastics such as PVC and
EIP are plastic-based materials. Both types of membrane are highly flexible and resistant to ultraviolet
radiation. They are also comparatively easy to install. But they are
also generally incompatible with one another and cannot be used in
combination on a single roofing system.
Steep Slope Roofing
Asphalt Shingles
Asphalt shingles are the most commonly used and among the least
expensive of materials available for steep slope applications.
They are very durable and are available in a wide variety of
colors and textures. Asphalt shingles consist of either an
organic (wood fiber or cellulose) or fiberglass mat which has
been saturated with asphalt and covered with colored mineral
granules. In climates where fungus growth is a potential
problem, granules treated with algecide are available.
"Self-sealing" shingles have an additional strip of adhesive on
the underside. The adhesive is activated by the sun's heat after
installation and "seals" each shingle to the one below it,
providing extra wind uplift resistance for the roof system.
Shingles were once available in only one thickness, but today
many manufacturers offer shingles where several layers have been
laminated together to produce three-dimensional profiles and
appealing shadow lines. These are known as "dimensional" or
"architectural" shingles.
Tile Roof Systems
Clay tile and concrete tile offer comparable benefits to slate,
but with greater variety and at less cost. Tile is very durable
and fire resistant. It is available in numerous profiles,
styles, finishes and colors. Tile is also less expensive that
slate (although it is also generally more expensive than asphalt
shingles and fiber-cement products). Like slate, however, tile
is relatively heavy, and its use may require roof reinforcement
to support additional weight factors.
Shake, Wood and Shingle Simulations
Wood Shakes/Shingles Wood shakes and shingles are made from
cedar, cypress, redwood, southern yellow pine and other woods.
Shingles are sawn on both sides to a uniform thickness and an
even taper. Shakes are generally split on one or both surfaces
for a more textured effect, and they tend to be thicker at the
butt end than shingles.
Fiber-Cement Roofing Materials products consist of cement and
organic or inorganic reinforcing fibers. They are designed to
combine the look of materials such as wood shakes/shingles,
slate and tile with advantages such as lower weight and higher
fire ratings.
Historically, wood shakes and shingles have been very popular in
California. In recent years, however, their use has declined
because of concern about their fire resistance. U.L. classified
wood shakes and shingles which have been pressure-treated with
fire retardants are readily available, but some communities
restrict or ban the use of wood roofing materials, regardless of
their fire rating.