Historic wooden shingle roofs

By Sharon C. Park, AIA

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

Most rehabilitation projects will involve competitive bidding, and each contractor should be given very specific information as to what type of shingles are required and what the installation details should be. For that reason, both written specifications and detailed drawings should be part of the construction documents.

For particularly complex jobs, it may be appropriate to indicate that only roofing contractors with experience in historic preservation projects be considered. By pre-qualifying the bidders, there is greater assurance that a proper job will be done. For smaller jobs, it is always recommended that the owner or architect find a roofing contractor who has recently completed a similar 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.
• The specifications also include instructions on removing the old roofing (sometimes two 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 be modifications to a standard product, such as cutting beveled butts, planing off residual surface circular saw marks, or controlling the mixture of acceptable widths (3"8"), these too should be specified.
• Every instruction for modifying the shingles themselves should be written into the specifications or they may be overlooked.
• The specifications and drawn details should describe special features important to the roof. Swept valleys, combed ridges, or wedged dormer cheek runoffs should each be detailed not only with the patterning of the shingles, but also with the placement of flashing or other unseen reinforcements.

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

-- NPS Preservation Brief 19