Generally, any physical change in a property will change its assessment. In Nassau County it takes about two years for the tax bill to catch up with the change in assessment due to construction or demolition. It is prudent to call our attorneys to discuss the changes you contemplate – even if you are not currently a client, for a no-cost consultation. Clients who are about to purchase a home which has had an older addition legalized by the seller should also expect to pay more in taxes in the future after the Assessor is notified of the addition.