A Study of backyard cottage policy in Seattle, Washington: existing conditions study, capacity analysis, and survey in conjunction with Seattle's Department of Planning and Development

Abstract

Backyard cottages or detached accessory dwelling units are a type of second unit found in single family residential areas. In Seattle, Washington backyard cottages were legalized in 2009. They are viewed by the Seattle Department of Planning and Development as an infill strategy to accommodate more dwelling units and a tool to increase affordable housing stock. After five years of legalization, the number of cottages is much lower than expected. Working with DPD, this thesis investigates backyard cottage policy, through the lens of data analysis of built cottages, capacity, and opinions of cottage owners. The first portion is a study of already built cottages, reviewing property values, median household income, and prevalence of apartments, second is a capacity analysis estimating the number of parcels where a cottage could be built, and lastly a survey of those with completed cottages seeking the reasons for cottage construction and what obstacles were present during construction. The four most important results from this study suggest that properties with cottages have higher property values than those without. Secondly, supply of parcels is not necessarily a barrier in preventing cottage construction. Third, cottages are built primarily to either accommodate family members or as an investment property where rental income will recoup the cost of construction. Lastly, high upfront costs and complicated and lengthy permitting are the largest obstacles for cottage owners.