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©1997-2000 Fred Tepfer 1380 Bailey Avenue Eugene, OR 97402 |
Why do we worry about roofs? If a roof leaks, it will almost inevitably damage
other building systems and building contents. Poor roofing investments steal
with compound interest. Here is a five step guide to getting the most for your
roofing dollar.
1. Inspection and Replacement Program
To avoid damage to and to maximize value, the basic goal of any organized
roofing program is to replace or repair a roof shortly before it wears out .
The first step in establishing such a program is to conduct a careful inspection
of all roofs, and to begin building a database which will ultimately include
the following information for each roof. If your district doesn't have such
a program, you can protect yourself by insisting that your roof be inspected
(with you in attendance) at least once each year.
Initially, the database may be limited to surface area, type, and estimated
life. Even this information is enough to plan and budget a replacement program.
2. Professional Detailing and Design
If you want to get maximum value from your roofs, it pays to hire professional
help in designing re-roofing projects on all but the very simplest buildings.
A design professional such as an architect specializing in roofs and waterproofing
can target your resources to the areas of greatest need and also ensure that
you are getting the best possible product for your investment. Generally speaking,
roofing contractors don't make good roofing consultants. They are less able
to consider non-roofing issues such as structural problems, thermal stresses,
roof drainage beyond the roof membrane itself, and how roofing material meets
other materials. Nearly any roofing material can perform either poorly or well
depending on design and installation. It's worth it to do it right in almost
all cases.
3. Appropriate Use of Materials
There is no single roofing material or installation system that is best in all
situations. What is most important is to select the most appropriate whole roof
assembly (substrate, insulation, membrane, ballast, etc.) as approved by the
manufacturer of the roof membrane, and to have it installed by a contractor
approved or licensed by the manufacturer.
substrates : Wood and steel are easy to fasten to, yet most
subject to damage from leaks. Concrete is very stable but more difficult to
fasten to.
drainage : Roof system must have at least 1/4" per foot
slope. If internal drains rather than gutters are used, each roof panel must
have an overflow drain. It is important to direct the overflow water to a place
that will be noticed by maintenance staff, who will then take action to clear
the primary drain. Perhaps the best place for an overflow drain to spill is
just over the window of the principal's office. Make sure that all metal components
of a roof system (flashing, gutters, drains, pipes, etc.) are of compatible
metals (no combination of galvanized steel with copper, for instance), to avoid
galvanic corrosion. It is not adequate to simply isolate these materials, as
water passing from one to the other is sufficient to cause corrosion in our
wet climate.
insulation : Rigid and batt insulation come in many types with
various R-ratings (thermal resistance). When re-roofing, it is always wise to
consider improving the insulation level of the roof. It is even more important
to select an insulation material that has the necessary compressive strength
if installed over the roof deck (to protect against damage from walking, etc.),
durability (when exposed to high temperatures, and so forth), and fire resistance
(if appropriate) to work in your roof assembly. Not only is it important to
select an insulation that matches the roofing material and installation system,
it is equally important to ensure that it is installed according to the roofing
manufacturer's requirements (such as joint staggering, material layering, etc.).
Remember that slope can be added to a roof by using tapered rigid insulation.
If designing a new roof, you can save money by designing most of the slope into
the structure and only using tapered insulation or other means to direct the
roof runoff to the drains.
roof membrane materials:
Built up roof (BUR), the traditional "hot tar"
roof, still works well if properly detailed and installed. Installation details
such as temperature of asphalt are of critical importance, so you may want a
manufacturer's warranty on the entire installation (thereby requiring a manufacturer-licensed
installer). Pick a cap sheet of light color in order to keep the temperature
of the roofing assembly lower on hot days.
Modified bitumen (mod bit) is similar in material to BUR, but is
applied in a single pre-manufactured sheet, often through a "torch-down"
application process. It avoids the problem of asphalt temperature, but other
installation details are very important, so contractor selection is still of
utmost importance.
Rubber roofs (EPDM, Hypalon, and other synthetic rubber materials)
are applied in large flexible sheets that are usually seamed with a solvent
cement. They can be glued to the substrate (fully adhered), held by special
fasteners, or covered with a layer of gravel or concrete pavers to prevent wind
uplift. The installation system should be designed for the structural substrate,
the strongest anticipated winds in your area, and other factors. Avoid using
small gravel for ballast as strong winds can pick it up and blow it through
the windows of the buildings down wind.
Poly Vinyl Chloride (PVC or plastic roofs) come in rigid sheets
that are cemented together. PVC roofs and flashings must be carefully detailed
to handle thermal expansion and contraction. Early PVC roofs failed from degradation
from ultraviolet light, but manufacturers have changed the formula in the plastic
to increase UV resistance.
Foam - and flow-on roof systems are fairly easy to install but
generally difficult to repair. They have not attracted a wide following.
Metal roofs can be manufactured in many materials, including aluminum,
copper, stainless steel, and coated steel. They are usually installed in batten-seam
or standing seam configurations, as shingles, or else as preformed rolled sheets
held by fasteners drilled through the sheet. Properly installed with the most
durable materials (such as a copper standing seam roof), they can last for generations.
On the other hand, if not properly installed (such as mixing incompatible metals
to create galvanic corrosion) or if of inferior materials, they will be neither
reliable nor durable. Metal roofs are usually installed at steeper pitches than
the other roof systems listed above. Attention to expansion and contraction
is essential.
Clay tile and glazed concrete tile roofs are durable and attractive.
If properly installed, clay tile can last a lifetime. Less is known about concrete
tile, as it is newer. Tile roofs are heavy, and structures must be adequate
to hold them. They also must be detailed to resist the winds anticipated in
your area.
Composition roofing: This roof material, which is used on most
homes in this country, is simple and economical to install onto a wood substrate.
Although not as long lived as some other roofs (15 to 20 years), it is fairly
easy to inspect and repair and inexpensive to replace. In the maritime Northwest,
consider installing zinc strips at the ridge to prevent moss growth or plan
for the need for chemical treatment to remove moss in shady areas.
Wood shingle and shake: Cedar and redwood shingle and shake roofs
are seldom used in schools. Unless treated with a fire retardant they present
a significant fire hazard. Recent materials appear to not provide an effective
life cycle cost. If used, they should be well ventilated underneath with an
attic.
flashing :
It is vitally important to design flashing to be appropriate to the various
substrates and roofing materials and to easily allow re-roofing and repair as
well as keeping the water out. This usually means using a two-part system of
flashing and counter flashing that can be taken apart. Avoid reliance on caulking
compounds for waterproofing. The flashing and roofing should have integrity
against water (including wind-blown water), with the caulking seal, if used,
providing a second layer of protection. Make sure that all long runs (over 20
feet) of flashing have provisions for thermal expansion and contractions.
4. Warranties:
Warranties should be from the manufacturer for materials and installation
on all but the simplest roof systems. Roofing contractors come and go, and,
given public bidding requirements, you will probably have little or no choice
in contractors.
5. Maintenance and Inspection:
Train maintenance staff and contractors to walk only on roof areas designed
for walking. The walkways should have a surface that protects the roofing material
and spreads out the load of the foot over a larger area. Concrete pavers are
sometimes used for this purpose on relatively flat roofs.
Keep a record of all roof repairs in your database (which will help tell you
that a roof needs major help).
Don't do anything except in emergencies (repairs, penetrations, remodels) on
a roof that is still on warranty without the written permission of the manufacturer
or you will probably void the warranty.
Inspect each roof at least once per year, with a written report to the roof
database.
Remember that when you re-roof is often the most economical time to undertake
seismic (earthquake) strengthening, so roofing projects should be planned in
conjunction with seismic upgrades.
Have roof maintenance and replacement planning be the responsibility of one
person.
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