If you would like to temporarily block off your street for your party, you will need to work with the Portland Bureau of Transportation (PBOT) to obtain a permit.
Insurance is optional for the permit. Permit fees are waived for the week of National Night out (weekend prior to NNO and weekend following NNO). You will also need to rent barricades from a barricade company, which usually costs about $50 for a basic street closure.
The details are explained on the Community Event and Block Party Street Closure Permits webpage on the PBOT site, and you can call their block party line at 503-823-4003.