Project Type: Evaluation, Design, and Construction Administration 
The Vital Structure: 

Research Lab Building Roof Replacement and Related Work

Issue

Vital Structures was retained to perform the evaluation, design, and construction administration for the replacement of EPDM roofs of the main building and low roofs located at the front of the building, which were approaching the end of expected service life, and previously reported to be leaking.

Diagnosis

Existing roof leaks were determined to be caused by deficient flashing transitions at the interface of the main roof and a parabolic standing seam metal roof at the front of the building. Leaks on the low roofs at the front of the building were determined to be related to deficient through-wall flashing in the masonry rising walls above the fifth-floor. Rooftop steel screen wall framing was also noted to be taking on water through holes in the tops of framing members. Cracks at the bases of steel screen wall supports were observed below the roof surface, due to developed pressure from freezing of entrapped water, resulting in interior leaks.

 

 

 

Solution

Our design included a new 90 mil EPDM membrane and ½” high density coverboard installed over the existing roof insulation. Due to low flashing heights, an abundance of rooftop mechanical equipment, and sloped steel rooftop screen wall framing members which interfere with the main roof edge, Vital Structures was granted a Code Compliance Variance from the Cambridge Inspectional Services Department, regarding the Energy Conservation Code requirements for above roof insulation, to help our client with existing hardship. Our design included new through-wall flashing at the fifth-floor masonry rising walls to provide drainage and to prevent moisture from entering the roof assemblies. To address damaged steel screen wall framing, our design included patching holes and breaches using fiber reinforced polymers and PMMA waterproof coatings, and repairing cracks at bases of steel supports via welding.

Result

The new roof system provides improved drainage due to the addition of crickets around mechanical units, which divert water towards internal drains. The drainage of the low roof was also improved by the addition of secondary overflow scuppers. Improved drainage makes the roof structure less susceptible to potential ponding related failure. Repairs to the through-wall flashing also prevents moisture from entering the conference room and laboratory spaces below. The structural integrity of the steel screen wall framing was restored, preventing further deterioration and damage to the screen wall.

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