Construction Intelligence

San Mateo Block 20 review details major excavation and 72 homes

San Mateo opens public comment on Block 20, a seven-story project with 72 homes, office space and two underground parking levels. Comments close October 29.

Published by BuildDetect on October 15, 2026

Perspective rendering of the proposed seven-story Block 20 mixed-use development at South Delaware Street and East 4th Avenue. — Proposed Block 20 development viewed from the intersection of South Delaware Street and East 4th Avenue. Rendering by ARC TEC, Inc., sheet A0.01 in the March 16, 2026 planning submittal published by the City of San Mateo. Proposed design. Original City of San Mateo project plans (PDF, page 2)

San Mateo has opened public review of a draft environmental study for Block 20, a seven-story office and housing proposal with two underground parking levels. A notice filed October 9 sets an October 29 comment deadline and identifies a November 17 Planning Commission hearing. (Filed October 9 notice)

The proposal at 500 E. 4th Avenue would deliver 72 apartments within an approximately 167,489-square-foot building. The October Initial Study describes approximately 99,025 square feet of office space and a maximum height of 85 feet. Michael Field of Windy Hill Property Ventures is listed as the applicant. (Filed October 9 notice; October 2026 Initial Study)

The mix includes 48 studios, nine one-bedroom apartments and 15 two-bedroom apartments. Twelve units would be below market rate. Office uses would occupy the ground, second, third and seventh levels, with residences on the fourth through sixth floors. (October 2026 Initial Study, printed page 7)

Excavation gives the proposal a concrete early work signal

The environmental study estimates roughly 47,278 cubic yards of soil export and excavation reaching approximately 26 feet below ground. It models an approximately 14-month construction period, a planning assumption rather than an announced start or committed delivery schedule. (October 2026 Initial Study, printed page 17)

That below-grade scope intersects with the site’s former gas-station history. The notice identifies 402 S. Delaware Street as a listed leaking-underground-storage-tank cleanup site. It says the county closed the case after remediation but requires notification of changes in land use or planned soil or groundwater removal. (Filed October 9 notice)

Proposed mitigation also addresses construction emissions, nesting birds, cultural resources and soil handling. The study calls for rooftop photovoltaic panels and all-electric building operation, while separately identifying an emergency diesel backup generator. (October 2026 Initial Study)

What contractors should watch

Trade relevance is an inference from the proposed scope: demolition, excavation and shoring, environmental soil management, concrete, waterproofing, electrical systems and rooftop solar warrant attention as design and approvals advance. The next verified checkpoints are the October 29 review deadline and the hearing scheduled for November 17. The records reviewed do not establish an open bid package, selected general contractor or issued construction permit.

Sources

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Architectural site plan for the proposed Block 20 development showing the building footprint and adjoining properties. — Proposed Block 20 architectural site plan, showing the building footprint and adjoining properties. ARC TEC, Inc., sheet A1.01 in the March 16, 2026 planning submittal published by the City of San Mateo. Proposed design. Original City of San Mateo project plans (PDF, page 32)