What Happens When Granny Moves In?

As families cope with the necessary care of an older relative, it’s important to consider the implications of adding another person to a decentralized wastewater system

An issue many people are facing with our aging population is what to do when it becomes necessary to care for older parents. For many, the answer is to have them come live with you. For those living on septic systems, this raises questions or concerns about the effects of bringing another family member into the home. At our workshops, we get questions about what will need to be done to ensure the system continues to operate.

The answer depends on each individual situation, what each parent’s health is, the need for privacy, the size and condition of the current system, and numerous additional factors. Below, we will give you a few ideas and thoughts about potential system impacts and solutions.

CRUNCH THE NUMBERS

We’ll start with understanding that the system operating in the backyard has a finite capacity. That capacity was determined by estimating the daily sewage flow. Often, this estimation was made based on the number of bedrooms in the residence. The design assumption often is water use of 75 gallons per person per day with 2 persons in each bedroom. For example, a three-bedroom house would have an estimated daily flow of 2 persons/bedroom x 75 gallons/person/day x 3 bedrooms = 450 gallons. Each state code has its own variations or deviations from this formula that can be used for adjustments. But since this is the accepted U.S. Environmental Protection Agency method, most states do not deviate far from this standard.

Septic tank capacity and soil treatment area sizing are based on estimated daily sewage flow. Whether the addition of grandma will have an impact on the system and whether changes need to be made is based on the current situation and the planned living space for her.

A simple example would be grandma moving into one of the bedrooms in the house that was vacated when the kids moved out and got married. Grandma is in good health, has no special needs or medications, and will not have separate meals. Here, the increase would be one person in addition to the two current residents. In this case, the estimated use for three people (3 x 75 gallons/day = 225 gallons/day) would be well within the design number of 450 gallons per day. Other than educating grandma about use of the septic system, there would not be any need for changes.

As most of us are aware, this example is usually not what happens. One of the issues with a parent moving in is the question of privacy for all individuals involved. This means that most often some level of modification or addition is made to the residence. Modification may involve putting in a separate entrance, addition of a separate bedroom and setting up a separate kitchen.

Where we live, this often means changing the basement from family room and recreation space to living quarters. In other areas, it probably means an addition to the house or an additional living structure or pod, tiny house, etc. In our area, we see living areas with separate access in garage lofts converted to living space as well as separate structures in the backyard.

SIMPLE OR COMPLEX

If the situation is converting basement space and if there was already a bedroom that was counted in the initial system design, there still may not need to be any septic system changes. Adding a bedroom automatically increases the flow estimate by 150 gallons per day. Changes in septic tank and soil treatment unit capacity will need to be made.

Let’s say there’s no additional bedroom but a kitchen is added so grandma can make her own meals in private. The picture begins to change. For a three- bedroom residence, the minimum size septic tank required by our code is 1,000 gallons. We feel this should probably be higher to begin with; but adding an additional kitchen certainly means there will be additional water use, so septic tank size will need to be increased. Using the most conservative method allowed in our state code would estimate this use at 142 gallons per day. This is basically adding the equivalent of another bedroom.

In these home expansion scenarios, septic tank capacity would need to be increased at a minimum from 1,000 gallons to 1,500 gallons, and with the increased kitchen waste, the recommendation would be to add 1,000 gallons of capacity. The current 1,000-gallon tank could be replaced by a 2,000-gallon tank or the addition of another 1,000-gallon tank placed in series.

Addition of the kitchen also means there will likely be an increased need for septic tank cleaning due to the introduction of additional solids. Changing health conditions will also trigger the need for additional maintenance. Blood pressure medications, having chemotherapy, and other health needs can upset the biological balance in the tank and result in solids not breaking down and settling, which will require periodic pumping to keep solids from clogging the effluent screen or (worse yet) passing through to the soil treatment and dispersal area.

Increased septic tank capacity and increased maintenance are only two of the potential impacts on the system and how it is managed. Next month, we’ll take a closer look at the trend of utilizing granny pods, the soil treatment area and management changes that can help mitigate the results of adding another person to the family home.



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