Reroofing - Page 1

11.0 General

11.0.1 A large percentage of all commercial/industrial roofing involves installing a new roof on an existing building. The process of specifying and installing a roofing system in a reroofing application can be more complex than that of specifying and installing a new roof. The design and installation team has to consider not only the new roofing system, but also the old roofing system, and any constraints imposed by the existing building. In many cases, the building is occupied at the time of reroofing, and the design and installation team must be sensitive to the needs and protection of the building occupants.

11.0.2 JM has prepared this section as a reference guide for architects, building owners, engineers, and roofing contractors, to assist in evaluating an existing roofing system and choosing a course of action for reroofing. The recommendations and suggestions contained in this section are a result of years of practical experience in the roofing industry. This section is not, however, a substitute for the services of a design professional who is able to take into consideration the specific details of a particular building and the building owner's requirements. No JM entity assumes any responsibility for structural design adequacy, performance of the roof deck, or of any other elements of the building system not included in the roofing system.

11.0.3 JM maintains a network of field Technical Service Specialists who are well versed in the problems and opportunities involved in reroofing. The location of the nearest JM Technical Service Specialist can be found in Section 13, "References", of the current JM Commercial/Industrial Roofing Systems Manual.

11.1 Evaluation of Existing Roofing Systems

11.1.1 One of the most important aspects of any replacement or recover project is the evaluation of the existing roofing system and support structure. Any evaluation should consist of investigating not only the existing roof system, but also the structural support system of the building. The condition of these two systems can have a significant effect on the performance of any replacement/recover system. The more accurate and comprehensive the preliminary evaluation, the more likely it will be to achieve a cost-effective and long-lasting solution to the problem.

11.1.2 Failure to conduct a meaningful and accurate evaluation can result in selecting a course of action which is inappropriate for that project, and may actually add to the problem, rather than solve it. For example, there are certain conditions which will make a recover system an inappropriate course of action. If any one of these conditions is identified at any point in the evaluation process, a recover system should not be considered, and the only appropriate course of action should be a roof replacement. These conditions include:

11.2 History of The Roofing System

11.2.1 Any evaluation should begin with a search of the existing records. Wherever possible, the original specifications and drawings should be located and consulted. These documents can be used to determine if the structural support system can withstand the added load of a recover system. A recover system should not be considered if the overall weight will exceed the original design load limits of the support structure. In this case, a total or partial replacement is the only acceptable course of action.

11.2.2 A search of the records should be made to determine whether a roofing bond/guarantee was issued for the existing roof system. If a bond/guarantee does exist, the terms and conditions should be reviewed and the issuer contacted, as necessary.

11.2.3 Original contract documents can provide information about the composition of the original roofing system, as well as the identity of the original roofing contractor. An interview with the original roofing contractor can provide valuable information regarding the "as built" circumstances and details.

11.2.4 Other documents, such as minutes from the pre-job conference,   reports by roofing inspectors, the manufacturer’s original roof specifications, and miscellaneous job correspondence can be very helpful in evaluating the system.

11.3 On Site Inspection

11.3.1 Following a careful investigation of the building records, an on-site evaluation of the existing roof system and support structure can be undertaken. This phase of the evaluation should include:

11.3.2 The following equipment may be useful for this phase of the evaluation: