Historic Preservation Commission Agenda and Packet 2011 12 19

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REQUEST: The applicant, Janice Hoffman, is requesting approval of a Preservation and Restoration Grant to allow for the existing roof to be restructured because it is undersized. The HPC /Council approved historic structure assessment (HSA) determined the existing roofing structure is substandard and must be retrofitted. Because the structure is a landmark, the HSA recommends retaining as many of the existing materials as possible. The roofing shingles, however, are not historic and may be removed. The following excerpt from the Technical Assistance memo prepared by JVA, dated April 6, 2011, states: "Our analysis indicates that the existing roof framing over the main portion of the house is severely overstressed. The rafters span approximately 17.5 feet from the eave to the ridge, far exceeding their capability. Supporting only the ceiling, the ceiling joists are capable of spanning from the exterior bearing walls to the interior bearing wall. But, the joists are overstressed when loaded by the intermediate line of support. Similarly over the Porch, the rafters have calculated overstresses exceeding Code allowed limits. "Recommendations: "Over the main portion of the house, the roof framing should be strengthened. The existing framing has significant calculated overstresses, localized areas of failure, and localized areas of excessive deflections. As such, the framing requires repair in order to be in compliance with the Code. "The design of such repairs is beyond the scope of this Memo. However, the following recommendations should be considered when determining the next steps: 1. Remove the intermediate lines of support in the attic in order to unload the ceiling joists and eliminate any further cracking in the ceiling finishes. 2. Support the rafter ends at the ridge. This would most economically be accomplished by constructing a wood stud cripple wall in the attic from the ridge down to the ceiling joists over the central bearingwall. Note that the capacity of the load path from the new wall through the first floor and basement bearing lines to the foundation would first need to be determined. Preliminary observations indicate that the existing bearing line is suitable to support this new cripple wall, although selective strengthening of the Basement level header beams should be expected. 3. Support the rafters at mid -span with diagonal web members or sister the rafters with engineered lumber. 4. Until repairs are performed, potential failures of portions of the roof framing could occur if overloaded by snow or wind pressure. It is therefore recommended that the roof framing be temporarily shored or that roof strengthening repairs be performed as soon as possible. Snow exceeding 4 inches in depth should immediately be removed from the roof. Snow removal should be performed from ladders or a lift so that workers are not on the roof concurrently with snow. "Further development of repair solutions is necessary to reliably estimate repair costs and those costs should be estimated by a contractor experienced with this kind of work. 3