Appeal 33632

2017 OPSC 1101.12

§1101.12.1: The location and sizing of drains and gutters shall be coordinated with the structural design and pitch of the roof.
§1101.12.2: Secondary (emergency) roof drainage shall be provided by one of the following methods specified in section 1101.12.2.1 or section 1101.12.2.2.
§1101.12.2.2: Secondary roof drains shall be provided. The secondary roof drains shall be located not less than 2 inches (51mm) above the roof surface. The maximum height of the roof drains shall be of a height to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by section 1101.12.1

This appeal is to allow for the removal of an existing through-wall secondary overflow scupper drain blocked by a new building addition. The existing affected roof has adequate structural strength to support ponding water to a height where it will overflow into adjacent roof portions to drain; a new electronic water alarm tied into the building automation system (BAS) will allow early warning of ponding water to building personnel.

• Two existing historic separate buildings (Mark Building and Main Building) will be interconnected by a new addition (Rothko Pavilion). This will allow for a single building consisting of three (3) separate structures (Main Building, Mark Building, and Rothko Pavilion).
• The Ayer Wing of the existing Main Building structure (built 1931) has a roof portion where an original through-wall overflow scupper will need to be removed to prevent potential water intrusion into the main public stair of the new Rothko Pavilion addition (Attachment 01).
• The inlet for the existing secondary overflow scupper to be removed is approximately 11-inches above the primary roof drain and is original to the 1931 construction. The scupper diverts ponding water through the wall to free fall to the ground.
• A proposed electronic water alarm will be installed no greater than 6-inches above the existing primary roof drain on an adjacent exterior parapet wall and will issue an alarm via the building’s BAS to alert building personnel when ponding water reaches the installed height of the alarm. The alarm will be an exterior-rated design with 120V power and low voltage connection to the BAS system (Attachment 02).
• Supplemental structural calculations show that the existing roof of the affected area can adequately support ponding water up to the height of adjacent roof ridges, after which the ponding water will flow into adjacent roof areas and to their respective roof drains (Attachment 03).
• The proposed electronic water alarm’s installation height of 6-inches maximum places it 5-inches below the elevation of the existing secondary overflow scupper to be removed.
• An existing sawtooth skylight demolished as part of the new project formerly drained onto the affected existing Ayer Wing roof; removal of this skylight reduced the roof area serving this drain and scupper by +/- 270 SF (Attachment 01).
• No further alterations to the affected existing roof are proposed.
• The existing Main Building is a listed National Historic Landmark, and the existing Mark Building is a Local Historic Landmark.

The new Rothko Pavilion addition will be built directly adjacent to the Portland Art Museum’s 1931 Ayer Wing of the Main Building, which will require an existing secondary through-wall overflow roof scupper to be removed to prevent the overflow water from entering the new Rothko Pavilion interior. A new secondary overflow drain cannot be installed into this roof without significantly impacting the historic interior of the Ayer Wing. An alternate was studied to install a new secondary overflow drain through the exterior parapet of the Ayer Wing and into the Rothko Pavilion, but no feasible path or connection point was found. A proposed electronic water alarm installed within 6-inches of the existing primary roof drain would allow for its installation on an adjacent exterior parapet wall above the primary roof drain. If ponding water were to reach the water alarm, a signal would be sent to the museum’s building automation system to alert personnel of an issue. This alarm would provide an earlier indication of a potential ponding issue than the original through-wall scupper installed at approx. 11-inches above the primary roof drain. If the alarm were to fail or if personnel could not reach the roof area in adequate time, the ponding water would overflow into adjacent roof areas and on to their respective primary/secondary roof drains. Supplemental calculations show that the existing roof structure for the area in question can adequately support this ponded water as it flows into adjacent roof areas. Roof elevations and slopes used in the structural calculations are based on original as-built drawings and have been verified in the field.

2017 OPSC §1101.12 requires the location of roof drains to be coordinated with the building’s structural design. Secondary roof drains shall not allow ponding of water to exceed that for which the roof was designed. The proposed design will allow for an early warning to building personnel via the museum’s building automation system for corrective action. The existing building’s roof has adequate capacity to allow ponding water to overflow into adjacent roof portions where it can drain.

CONCLUSION:
It is proposed that an existing through-wall secondary overflow scupper be removed for a portion of the 1931 Ayer Wing since the existing roof has capacity to support the ponding water to a point which it will overflow to adjacent roof areas to drain. A new electronic water alarm will be installed not greater than 6-inches above the primary roof drain of the affected roof area to allow early warning to building personnel via the museum’s building automation system.

Relevant Attachments:

• ATTACHMENT 1 – Roof Plan and Existing Context
• ATTACHMENT 2 – Proposed Electronic Water Alarm – Tank Alert XT
• ATTACHMENT 3 – Structural Calculations for Ayer Wing Roof Scupper Disconnect – KPFF dated 12/09/2024