There are a number of things that affect this answer. If the house has a private sanitary system you should contact the County zoning office to see if there are limitations to house additions. Whether a house is conforming or not for any reason may affect house addition allowances.
Setback requirements and measurements should be checked to see if there is room to add onto a garage or house. Most properties have limitations regarding garage or accessory building square footage based on the size of the property and the zoning district. For those towns that have not adopted County zoning, contact the town for that information.