Reroofing - Page 5

Reroofing Options

11.14 General

After the old roofing system has been thoroughly evaluated, alternatives can be examined. Simple maintenance may be adequate up to a point. As a statement from the National Institute of Standards and Technology (formerly the National Bureau of Standards) reads, however, "There comes a time in the life of a roof on every permanent structure when it is no longer practical or economical to effect repairs, and when that time comes, reroofing is the only solution."

The selection of an appropriate reroofing system depends upon many factors. In new construction, it is possible to design a roof system by gathering data from drawings, engineering calculations and specifications for related components. When reroofing, however, the new roofing system must fit the existing structure and conditions.

After collecting all background data and conducting physical inspections, a course of action may be determined. The choices are:

11.15 Replacement

11.15.1 The complete removal of the old roof system is always the best and safest option. In this way, all questionable materials are eliminated. There is no possibility of inadvertently leaving any wet or deteriorated insulation in the new system. Questions of asphalt, membrane or insulation incompatibilities are not a concern, as they would be in a recover system.

A complete tear off will also reveal problem areas in the structure and deck assembly, if they exist. Deck panels may be found to be deteriorated and in need of replacement because of leakage over an extended period of time. Deterioration of the deck and fasteners may not only be caused by leakage, but may also be due to a condensation problem, revealing the need for a vapor retarder.

A good solid deck is essential. Any rusted, decayed or otherwise damaged deck should be replaced. Without a sound base, the new roofing system cannot be expected to perform over the long term.

11.15.2 Considerations

When designing a replacement roof system, additional roof components or features may be required because of the occupant’s changing needs, or to accommodate changes in interior conditions. For example, a new manufacturing process may now be housed inside the building, or perhaps an old manufacturing facility is now an office building. In most circumstances, when specifying a roof system in a total replacement, any JM membrane and insulation system appropriate for that particular deck may be used.

11.15.3 Adding Components

Insulation. Many older buildings are seriously underinsulated by current standards. The owner may wish to upgrade the thermal performance of the roofing system to provide a more comfortable environment for the occupants of the building, as well as to reduce energy costs. Before adding significant amounts of insulation, however, careful consideration should be given to potential condensation problems created by the additional "R" value. For more information, consult "Vapor Retarders", Section 5, of the JM Commercial/Industrial Roofing Systems Manual.

Expansion Joints. Prior to removal of the old roof, the location of splits, diagonal wrinkling in base flashings, or other signs of differential movement should be noted. If these indications are present, the designer should consider the addition of expansion joints and expansion joint covers. See Section 10 on "Roofing Accessories" and Section 4 on "Roof Decks" for more information.

Additional Drainage. One of the most common problems found on older buildings is the lack of proper drainage. Many were designed with "dead level" roof decks, and in theory, drainage should be adequate. Unfortunately, it rarely is. Elevations of columns are never exact and deck units may have a slight camber or curvature, which, under normal deflection of the deck from the weight of roofing and rooftop equipment, can cause portions of the roof deck to sag below the level of the drain. This is especially true if the drains are located at columns. Even if slope was provided originally by varying the height of columns and girders, the roof may not drain, due to settlement of the building. A clogged drain that has allowed water to build up can also result in a permanently deformed deck.

The most effective way to provide proper drainage on an existing structure is to install a factory-tapered insulation system. These tapered insulation systems can be custom designed for the individual drainage requirements of practically any building, and they afford the owner higher thermal performance. For more information on tapered insulations, contact the JM Tapered Systems Group at 800-343-1283, or 800-341-8032.

Small areas of ponded water can possibly be treated with the addition of sumped roof drains. Ponding that occurs between existing drains or scuppers can be treated by the addition of crickets or saddles between these features.

11.15.4 System Selection

Of all the reroofing alternatives, total replacement allows the designer the greatest latitude for selection of a replacement system. Any JM commercial/industrial roofing system appropriate to the deck type may be used when the existing system is totally removed.

11.16 Partial Replacement

11.16.1 Partial replacement normally entails removing an existing membrane and any damaged or wet insulation and installing new insulation and a new membrane.