WA state real estate law, land use and zoning issues, open spaces zoning, procedure for changing zoning status

Are you located in unincorporated Snohomish County? If so, you can view Title 30, the Unified Development Code here: http://www1.co.snohomish.wa.us/County_Services/county_code.htm.

Yes. Open space zoning is not your average 'you can build a house' (or for that matter anything else) area. The zoning rules are going to be somewhat different for each municipalitiy/ government entitiy. For example, the City of Snohomish has an OS (Open space) zone which is mainly parks and ballfields, City of Arlington does not have an OS zone, Snohomish County has agriculture, forest and open space zones. You are going to need to check the rules which apply to your property. But, in general you are probably going to need to change the zoning if you want to build a residential dwelling unit. Just contact the planning department which has control of your property and ask for their help in gathering information. At some point you are probably going to need the assistance of an attorney or a planner or land surveyor to help you with your project.