ADU & Home Additions in Hillsborough

California state law allows detached ADUs up to 1,200 sq ft and Junior ADUs up to 500 sq ft. In Hillsborough, lot coverage limits (typically 25-35%) may constrain the maximum size if your property already has significant building coverage. We conduct a thorough lot analysis to determine the maximum allowable ADU size for your specific property.

We prepare a complete ADRB application including architectural drawings, 3D renderings, material samples, and a landscape plan showing how the ADU integrates with the property. The Board meets twice monthly. Most ADU applications are approved in 1-2 hearings (4-8 weeks). We attend hearings with you and address any Board questions directly.

Yes, subject to height limits (typically 36 feet) and ADRB approval. Second-story additions in Hillsborough must be architecturally compatible with the existing home and sensitive to neighbor sight lines. We design additions that look like they were part of the original home — matching roof pitch, window proportions, and exterior materials.

Total timeline is typically 12-16 months: design (6-8 weeks), ADRB review (4-8 weeks), building permits (6-8 weeks), and construction (5-8 months). Some phases overlap. We provide a detailed project timeline at our first meeting so you can plan accordingly.

A well-designed ADU that complements your Hillsborough estate can add $350,000-$600,000+ in property value — typically exceeding construction costs. Guest houses and in-law suites are highly valued by Hillsborough buyers, particularly those with multi-generational families. The key is architectural quality that matches the main residence.

Yes — garage conversions to ADUs or living space are permitted under California law. In Hillsborough, the ADRB may require that a replacement garage or carport be constructed to maintain neighborhood character. We often design combined projects: convert the existing attached garage to living space and build a new detached garage that also houses an ADU above.