Multnomah County, OR Building Setbacks & Zoning: Lot Coverage Limits (2026)

Portland City Code 33.110.225 sets maximum building coverage in single-dwelling zones: R20/R10 (30%), R7 (40%), R5 (50%), R2.5 (60%). Building coverage is calculated as the total roofed footprint of all structures on the lot. Portland's Clean River Rewards program and Stormwater Management Manual (Title 17) require on-site stormwater management for new or redeveloped impervious surface over 500 sq ft in most cases, using rain gardens, drywells, eco-roofs, or permeable paving. Impervious surface coverage is distinct from building coverage - driveways, patios, and walkways count against impervious limits but not building coverage unless roofed. Gresham Development Code sets residential coverage at 40-50%. Troutdale permits up to 40% in R1 and 55% in R3. Unincorporated Multnomah County MCC 39 Rural Residential zones cap at 25% building coverage with much larger minimum lot sizes. MUA-20 allows 15-25% coverage depending on parcel use. EFU parcels have dwelling footprint limits rather than coverage percentages. Permeable pavers and eco-roofs may receive partial credit under stormwater rules. Coverage violations require adjustment (variance) and can delay permits significantly.