03 November, 2023
Mike Roberts and Jeff Brown
City of Hercules
111 Civic Dr.
Hercules CA
Re: City of Hercules- Library Story Cone
Memo on recommendations and next steps based on learnings from the water intrusion field test.
SERA Project No. - 2303102.01
Dear Mike and Jeff,
On September 19th, 2023, McGinnis Chen Associates (MCA) and SERA performed a leak investigation at the Story Cone building at the Hercules Library in Hercules, CA. MCA + SERA understand that water intrusion has been reported each winter for years, specifically near the head of the window at the East Elevation at the Story Cone. Water intrusion was also reported on the floor along the South Elevation.
MCA was able to recreate the leak on the floor at the south end of the Story Cone and observed moderate water staining and corrosion surrounding the window at the East Elevation. Observations are:
1. Leak recreated at South Elevation:
Water spray was applied at a crack in the cement plaster (stucco), which was approximately 6 -feet long and existed approximately 8-feet above-grade on the exterior wall. Water intrusion was observed entering the interior at the base of wall.
2. Leak at window head:
SERA observed that the window was designed and documented as a manufactured storefront window but was changed during construction and installed as a channel-set glass assembly made of individual components assembled in the field. These assembled components would not perform as a manufactured and tested storefront assembly.
Metal flashing is integral to a window assembly at all sides of the opening that allow trapped water to escape the wall assembly; however, at the Story Cone these have been closed off with sealant and trap water in the wall assembly without a path to the exterior. Due to the slope of the Story Cone walls, the most natural path for trapped water would be toward the interior finishes of the wall. Moderate water staining, corrosion, and insufficient rough opening flashing were observed surrounding this window at the interior.
3. Skylight:
The available design documents for the skylight convey discontinuous waterproofing where the wall framing meets the skylight. According to the original details, the vertical metal flashing directly beneath the skylight is the sole barrier to resist water intrusion at that location. The detail would be ‘sealant dependent’ and the laps in the metal flashing would need a perfectly installed sealant embedment which cannot have any deficiencies in its application. MCA observed metal flashing laps that were deformed as well as laps that did not display sealant bleed-out.
Since these water intrusion issues have been experienced by the City over the past few years and all efforts to curb the leaks have been unsuccessful, SERA and MCA recommend the following mitigation efforts:
1. Remove existing window assembly and reinstall a new window assembly with new flashing details.
MCA observed that the window's rough opening flashing appears to be inadequately installed which is resulting in water staining, leaks, and corrosion as observed in the leak investigation conducted on September 13, 2023. Additionally, the stucco at the head of the window is not detailed to enable weeping of the water in the system. This compounds any discontinuity of the flashing as the water within the stucco system is directed to the interior rather than allowed to weep to the exterior.
Our recommendation is to remove and reinstall the waterproofing around the window. This procedure would require part of the stucco and the window to be removed to allow for waterproofing flashing to be redone. During the removal it is likely that the window could be cracked and damaged.
2. Remove existing skylight and reinstall new skylight assembly with new flashing details.
Original Drawings show non-continuous waterproofing at the Story Cone skylight. The waterproofing stops short of the skylight and does not tie into the assembly. The metal flashing at the bottom of the skylight appears to be the only water barrier as it transitions from the skylight to the rough opening. Our recommendation is to replace the flashing, waterproofing assembly, and skylight to allow for proper flow of water off the skylight.
3. Remove entire stucco surface and reinstall. This is an optimal solution as compared to multiple spot demolition and patch solutions which may provide opportunities for future intrusion.
MCA noted several deficient conditions at the story cone window, skylight, and stucco assemblies. The story cone utilizes a loose laid building paper as its air/water barrier, which is an industry bare minimum requirement for stucco assemblies. The current stucco also shows signs of damage and cracking which will exacerbate any pre-existing design inadequacies.
It is SERA and MCA’s professional recommendation to replace the entire existing assembly with a fully adhered and vapor permeable air/water barrier with a new stucco finish. Without this comprehensive solution to the entire assembly, it is our professional opinion that leaks will continue. There is not a fluid applied membrane approach that will adequately seal the existing stucco surface, while simultaneously allowing the structure to breathe.
In summary, to fully address the leaks on the Story Cone, we recommend replacing the window and skylight with improved flashing details and removing and reapplying the stucco on the cone.
Sincerely,
SERA & MCA
attachments: Hercules Library Story Cone Markups