Alterations to a property in which public sewer is not available is regulated in part by Section 19-13-B100a of Connecticut's Public Health Code.  The alterations include building conversions/changes in use, building additions, garages/accessory structures, swimming pools, and lot line changes. 

The alterations will NOT be permitted unless the Health Department has determined that, after the alteration, a code complying area exists on the lot for the installation of a septic system.

The determination is made based upon existing soil data. If the data is insufficient or nonexistent, it is the responsibility of the property owner to perform the soil testing. Once a code complying area has been identified, portions of the property outside this designated area may be utilized for further development. 

Septic systems for the typical home are sized based upon the number of bedrooms. As such, some modifications, such as a finished basement or adding a study, could possibly be considered adding a bedroom under the Public Health Code. This may or may not present a problem, because the Public Health Code allows up to a 50% increase in design flow without increasing the size of the septic system, providing the addition meets all of the other requirements of the Public Health Code. To be considered a bedroom it must meet the following conditions:

• Be a habitable or planned habitable space per the Building Code
• Provide privacy. A large cased opening (minimum 5 feet width and no doors) can be installed to eliminate privacy.
• Have convenient access to a full bathroom, containing either a bathtub or shower
• Entry is from a common area, not through a room already deemed a bedroom