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Specifications for Replacement Roof

By The Old House Web
>>Introduction >>Roofing practices to avoid
>>History of wood shingles in America >>Maintenance
>>Historic detailing and replacing roofs >>Taking it further
>>Specifications for the replacement roof  

By Sharon C. Park, AIA

Specifications and roofing details should be developed for eachproject. Standard specifications may be used as a basic format, but they shouldbe modified to reflect the conditions of each job. Custom shingles can still beordered that accurately replicate a historic roof, and if the roof is simple, anexperienced shingler could install it without complicated instructions.

National Park Service employees work on replacing the wood roof on the historic Spangler Barn in Gettysburg, Pennsylvania.

Mostrehabilitation projects will involve competitive bidding, and each contractorshould be given very specific information as to what type of shingles arerequired and what the installation details should be. For that reason, bothwritten specifications and detailed drawings should be part of the constructiondocuments.

For particularly complex jobs, it may be appropriate to indicate that onlyroofing contractors with experience in historic preservation projects beconsidered. By pre-qualifying the bidders, there is greater assurance that aproper job will be done. For smaller jobs, it is always recommended that theowner or architect find a roofing contractor who has recently completed asimilar project and that the roofers are similarly experienced.

  • Specifications identify exactly what is to be received from the supplier,including the wooden shingles, nails, flashing, and applied coatings.
  • Thespecifications also include instructions on removing the old roofing (sometimestwo or more earlier roofs), and on preparing the surface for the new shingles,such as repairing damage to the lath or sheathing boards.
  • If there are to bemodifications to a standard product, such as cutting beveled butts, planing offresidual surface circular saw marks, or controlling the mixture of acceptablewidths (3"8"), these too should be specified.
  • Every instruction formodifying the shingles themselves should be written into the specifications orthey may be overlooked.
  • The specifications and drawn details should describe special featuresimportant to the roof. Swept valleys, combed ridges, or wedged dormer cheekrunoffs should each be detailed not only with the patterning of the shingles,but also with the placement of flashing or other unseen reinforcements.

Thereare some modern products that appear to be useful. For example, paper coated andreinforced metal laminated flashing is easy to use and, in combination withother flashing, gives added protection over eaves and other vulnerable areas;adhesives give a stronger attachment at projecting roofing combs that could blowaway in heavy wind storms. Clear or light colored sealants may be less obviousthan dark mastic often used in conjunction with flashing or repairs. Thesemodern treatments should not be overlooked if they can prolong the life of theroof without changing its appearance.

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-- NPS Preservation Brief 19

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