|Plan-link posting and reply, October 25, 2007
Q: Has the language for in-law apartments become a thing of the past? Is the new direction to use accessory apartments? If so, is this due in part to the new state-wide building code which uses the term duplex? I'm trying to get a handle on whether we should have an in-law clause, and an accessory apartment ordinance. Examples of what has worked or not worked are very helpful...
A: The "correct" term is accessory dwelling unit (enabled through RSA 674:21), which helps to clarify that such units do not need to be restricted to family members. A duplex is not an ADU, irrespective of any changes to the statewide building code. Generally speaking, in a duplex you have two dwelling units that are essentially equal in their impact—they each form two halves of a single primary use, which is a two-unit residential structure. With an ADU, the primary use is single family residential, to which the ADU is accessory and hence, subordinate. It is certainly appropriate to place regulatory restrictions on how ADUs can be developed and used, whether they are a use by right or by some conditional approval (e.g, special exception, conditional use permit).
There is a section on ADUs in the NHHFA publication, "Housing Solutions," which is currently being updated but is still available. See chapter 3 in particular.
One thing you’ll probably find is that imposing a familial restriction is difficult to enforce (who’s going to do the DNA testing?). ADUs offer a homeowner the ability to "downsize" his or her home without actually having to move. It’s a great option for older residents who want to continue "aging in place," and provides a ready source of income for the owners. The property gets taxed at a higher rate because of the added value of the ADU, and the ADU itself provides new affordable housing with minimal impact upon surrounding properties, the environment, schools, etc. If the house has on-site sanitary disposal, however, you do need to ensure that the septic system has capacity to handle the added load, which might require a new design to be permitted even if it is not initially constructed (kept on file to demonstrate capacity in the event of failure).