In the City of Seattle, month-to-month tenants are protected by the Just Cause Eviction Ordinance. SMC 22.206.160(C). Under that law, their tenancies cannot be terminated unless you have one of the 16 just causes and you give them a notice of termination specifying the applicable just cause. "Rehabilitation" is one of the just causes, but it requires a 90 day notice, a tenant relocation permit issued by the City, and payment of relocation assistance to eligible tenants. To obtain the permit, you must also be applying for construction permits.
The Seattle Department of Planning and Development website provides several guides for obtaining a license. To start the process, you will have to meet with a member of the landlord and tenant assistance unit. The City estimates the process takes about 180 days.
You are permitted to terminate a Section 8 tenant with a month-to-month tenancy if you intend to renovate the unit. 24 CFR 982.310(d)(iv). This is a type of “other good cause” that generally requires at least 30 days’ advance written notice specifying the grounds for the termination, but you should consult your Housing Assistance Payment contract with the public housing provider and your lease for more details. You must comply with the requirements of both laws to property terminate the tenant.