A ROOFING PRIMER FOR SCHOOLS

2006 Fred Tepfer
1380 Bailey Avenue Eugene, OR 97402
non-commercial use freely granted
 

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Why do we worry about roofs? If a roof leaks, it will almost inevitably damage other building systems and building contents and serious threats to the health of building users. 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 if necessary) 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. With simple tracking, you will know when the investiments in repairs outstrip the amortized cost of a replacement roof. Roofs wear out on fairly reliable schedules, so building reserves can be built for specific roof project targets. After a number of years, you can also use this database to determine which roofing systems have the best price/performance ratio for your district.

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, interaction of seismic upgrade with re-roofing projects, 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 and corrosion-resistant but can be more difficult to fasten to.

drainage : Roof system must have at least 1/4" per foot slope. If internal drains rather than gutters on the outside edge of the building 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 or secretary'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 board and flexible batt (blanket-like) 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 as well as installer'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 (see other articles on sustainabilty, energy, and heat island effect for other advantages of light roof colors).
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 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 rock 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 downwind.
Plastic roofs (PVC, TPO, etc.) 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, but the performance issues of PVC have led to most installations of this type being the newer TPO roof, which hasn't developed as many problems but which is too new to develop a substantial track record.
Foam - and flow-on roof systems are fairly easy to install but generally difficult to repair. They have not attracted a wide following in school applications.
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. Many schools currently use steel roofing in standing seam configuration, made from steel that is both galvanized (zinc-coated) and painted.
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 heavier than other roof materials, and structures must be adequate to hold them. They also must be detailed to resist the winds anticipated in your area. Careful attention to installation details at penetrations, valleys, hips, and ridges is essential to a leak-free installation.
Composition roofing: This roof material, a mat of fiberglass or other materials impregnated with asphalt (a petroleum product) and covered with small mineral beads is used on most homes in this country. It 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, moss growth can become an issue where the roof is shaded. Although it has a fire-resistant top surface, it is flammable and represents a considerable amount of fuel. It should not be used in areas subject to wildfires.
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.

roof color:
Installing a light-colored or white roof can dramatically reduce the heat load inside the building. A ventilated attic under the roof can also help keep the interior cooler. A light roof will also keep the area around the school cooler (heat island effect). If the building is mechanically cooled (has air conditioning), a light color can substantially reduce energy costs. In cool maritime environments that very seldom have cooling issues, dark colors can provide some solar gain and reduce heating loads.

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. Some public agencies divide their roofing projects into smaller parts to allow them to use a select list of bidders under public bidding rules for small projects (varies from state to state).

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. Walking mats are also available. Walking surfaces vary depending on the roofing type.
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. Meet at least once per year to discuss these inspections and to plan upcoming maintenance and replacement.
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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