Project Type: Structure, Roofing, and Evaluation.
Low Slope Roof Replacement with Structural Roof Framing Modifications
Issue
Vital Structures was retained to perform an evaluation of the existing, 18-year-old, low-slope PVC roof of the two-story commercial building located in historic Harvard Square, Cambridge, MA. The building included a long-standing restaurant on the lower floors that experienced a fire at the rooftop mechanical equipment, which damaged the equipment and the existing roof system. Existing conditions included aging rooftop mechanical units that serviced the restaurant and office space at the second-floor level. Other concerns included a questionable existing parapet/pediment bracing at the North/front elevation of the building’s roof area and aesthetic design requirements of the local Harvard Square Historical Commission.
Diagnosis
There were several areas of concern with the existing 2000 low slope PVC roof system including multiple roof patches, fire damage and the generally aged roof membrane. Vital Structures performed an evaluation of the existing PVC membrane roof system; including a review of limited original design documents, exploratory test cuts, and a comprehensive evaluation of the roof system including structural review per 2015 IEBC Chapter 7 – Alterations Level 1, structural analysis for new rooftop HVAC equipment loading, roof drainage calculations, insulation energy code requirements review, and localized wood roof deck evaluation for replacement. The following conditions were noted by Vital Structures:
- The existing PVC roof system had surpassed its useful life expectancy and required removal and replacement. The new roof system was to include high puncture and chemical resistance due to expected rooftop equipment maintenance and restaurant exhaust containing grease discharge.
- The existing rooftop HVAC equipment, rooftop ductwork and supports were aged with questionable ductwork supports, all requiring removal and replacement (HVAC Engineering by others).
- Roof framing modifications and upgrades were required for the new rooftop HVAC equipment, parapet pediment bracing required by building code and other future rooftop equipment needs.
- The existing steel parapet/pediment bracing was questionable and attached only to the ¾-inch tongue and groove wood roof deck. A new steel parapet/pediment bracing system with associated building roof framing connections was required.
- Improper/non-building code-compliant overflow roof drainage plumbing was identified.
- An existing rooftop brick chimney was observed to be in disrepair and confirmed to be abandoned and not needed.
Our Solution
Vital Structures prepared a roof evaluation summary with evaluation findings, roof structure review per 2015 IEBC Chapter 7 – Alterations Level 1, and structural gravity with snow load analysis for the new rooftop HVAC equipment. General recommendations, and options for the roof system(s) replacement and the required structural modifications for the roof framing for the new HVAC equipment were provided. Vital Structures was tasked with the new roofing systems design and structural roof framing modifications, including limited bid assistance and limited construction administration for the project. The evaluation, design and construction included the following:
- Complete removal of the existing PVC roof, roof accessories and HVAC equipment.
- Roof framing modifications with laminated veneer pre-engineered lumber, structural connections and localized wood roof deck repairs for new rooftop HVAC equipment, new parapet/pediment steel bracing to meet current building code requirements for unreinforced masonry parapets.
- Full roof replacement including new KEE/Elvaloy roof membrane providing more durable and chemical resistant roof membrane.
- The removal and replacement of perimeter edge blocking, localized wood roof decking replacement. New roof system included full vapor barrier, adhered, energy code compliant R-30 roof insulation and high density polyisocyanurate cover board.
- Utilize an adhered insulation assembly to eliminate any exposed insulation fasteners at the exposed second floor office space ceilings.
- New copper coping caps to meet local historical district requirements.
- New internal roof drain with properly plumbed/code compliant overflow roof drain.
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