Replace Asbestos-Cement Roofing on the Historic Maintenance Shop (Fort Building 527)
Fort Yosemite is located within the Yosemite Village Maintenance Area in Yosemite Valley. The project would remove the existing, highly degraded asbestos-cement (Transite) roof shingles and replace them with visually in-kind metal shingle roofing. Many of the existing roof shingles are cracked, missing in some areas, blowing off in the wind, and falling to the ground, where asbestos particles are broadcast into the air. The remaining shingles are very brittle and the roof sloughs more pieces to the ground whenever maintenance staff walks on the roof for repairs. The Transite shingles, tar paper, and mastic were installed in 1935. They were tested in Oct 2019 by Leon Environmental Services and determined to be asbestos-containing material of 15%, 30%, and 10%, respectively. According to EPA and CAL-OSHA regulations, materials containing greater than 1.0% asbestos by weight are considered asbestos containing material, requiring any renovation, demolition, and disposal of this material to be performed by trained, licensed asbestos abatement contractors. Falling and deteriorating asbestos shingles present a health hazard by releasing asbestos fibers into the air. Because it is so hard to destroy asbestos fibers, the body cannot break them down or remove them once they are lodged in lung or body tissues. They remain in place where they can cause diseases such as asbestosis, lung cancer, and mesothelioma. Many park staff use this building, as it houses the Buildings and Grounds, Custodial, Roads, and Utilities crews for Yosemite Valley, as well as the Fire Station, Law Enforcement, and Jail. There have been a number of Freedom of Information Act requests from building occupants regarding the safety of working in and around this building. The park proposes to contract with a hazardous materials contractor to remove the shingles, tar paper, and flashing (with asbestos containing mastic).
The existing 3x8 sheathing will be replaced in kind where rotted or water damaged. The park would then install 15/32" structural plywood sheathing over the existing 3x8 sheathing, over which ½" fire rated Dens-Deck Prime gypsum material, and a Grace Ice and Water HT, or equal, self-adhesive weather barrier will be installed. The new roofing will consist of a steel shingle interlocking roof system with a 20 Year Watertight Warranty and a 25 year warranty against structural failure and perforation, in a color and texture that mimics the existing Transite shingles, Centura Steel Shingles, with a special run of wood grain embossing. The metal roofing shingles will be gray in color and have been selected in coordination with park cultural resources staff to best match the appearance of the existing asbestos shingles (attachment 5: specs, example). The new roof membrane will provide a leak-free, asbestos-free, Class A fire rated metal roof to protect the building from further decay.
This project will remove and abate asbestos-cement roof shingles and asbestos containing tar paper installed in 1935 from the Yosemite Valley Maintenance Building ("The Fort"), Building 527.