U.S. short-term rental supply hit record highs in 2022. That means more of your customers may be renting out their vacation homes either part time or full time. Vacation home rental can create numerous challenges that can be addressed during the design and installation of a new septic system for the property. If these issues are not dealt with, the performance and life expectancy of the system may be negatively impacted. Unaware property owners could irreparably damage their system if these issues are not addressed. During design and installation of a new system that serves a vacation home, you need to consider the overall hydraulic load, peak load and usage concerns.

1. Overall hydraulic loading

Problems: When you are designing and installing a new system in a location where rentals are common, the first question to ask your clients is how they plan to use their property. Some cabins, cottages and vacation homes are used on a very limited basis, while others are heavily used. Homes rented through one of the online vacation rental services will often be fully occupied during peak periods, which can vary based on the location.

You must get honest answers from the owner regarding how many beds are in the home as many times occupancy will exceed the typical assumption of two people per bedroom. Vacation home rentals often have multiple beds per bedroom, pull-out sofas, futons, air mattresses and occasionally a bunk house. It is common to find a four-bedroom home advertised to sleep 10, 16 or even 20 people! With high flows, septic tanks are more likely to have turbulent conditions decreasing settling and causing downstream components to deal with more solids.

Solutions: 

a. For the design flow: Add 50 gallons per person to the occupancy beyond two people per bedroom. If the vacation home is being rented, gathering existing flow data is a great idea to verify average and peak flows. The owners may also consider limiting the occupancy to match the design flow.

b. For septic tank capacity — take the calculated design flow and multiply by three to determine septic tank capacity.

c. Add a large effluent screen to catch solids and add an alarm to notify when cleaning is needed.

d. Be sure to use calculated design flow (or flow equalized design flow) for sizing any advanced pretreatment or the soil treatment area.

2. Peak loading

Problems: Peak loading can be an issue with any vacation or second home. And it is even more likely with those used as rentals. Large peak flows tend to happen on days when one family leaves and the next arrives. On these days the entire home is typically cleaned and all the towels and bedding being laundered. Remember that state code values for bedrooms are to be viewed as a peak flow that should not be exceeded on any given day and that average flows should be less than 70% of these values for system longevity. 

Solutions:

a. Discuss management options with the owner — would they consider having double sets of towels and sheets and laundering them offsite? Would they lower the allowed number of occupants?

b. Include timed dosing with the treatment system designs that include a pump. Timed dosing configurations include an adjustable timer that controls pump rest interval and runtime to spread out the application of wastewater over time versus how it is generated in a typical home or other facility. This will not help prior to the septic tank but it will help downstream components perform better.

Utilizing timed dosing instead of demand dosing mitigates variations or peaks in wastewater flow. Peak flows from the dwelling are stored and then dosed to subsequent components evenly throughout the day. Usually, the flow for one day is equalized over a 24-hour period, but it can be done for longer periods of time, especially if peak flows last for longer than one full day. For this to be accomplished, the tank must be large enough to handle these flows. The pump tank capacity for a single-family residence using flow equalization should be at least two times the daily design flow.

3. Usage

Problems: Large groups gathering in vacation homes often lead to large meals being prepared, creating extra food waste entering the system — and larger volume of food waste if a garbage disposal is present. In addition, commonly people renting vacation homes are not aware of the do’s and don’ts of what should go down the drain with septic systems. This can result in many inappropriate items being flushed down toilets and washed down drains.

Solutions:

a. Discuss management options with the owner. Removing the garbage disposal may sound extreme but is a very effective way to decrease the loading to the system. Use and provide biodegradable cleaning products, as well as soaps at sinks and for laundry that will also lessen the load to the septic system. Be sure all cleaners and sanitizers used in the home do not contain “quats” (ammonium chloride is the active ingredient) as these strong sanitizers are very hard on the needed beneficial bacteria in septic systems. 

b. Provide educational materials — the U.S. Environmental Protection Agency has great flyers developed for rental properties that can be provided prior to check-in, and then hung up or placed in kitchens and bathrooms. Search online for EPA Septic Smart Educational Materials.

c. If it is an existing vacation home, sample the effluent from the septic tank and compare it to normal septic tank effluent levels. If they are higher than normal, up-size components based on these elevated levels. Increasing the septic tank size and adding an effluent screen will help to decrease these levels but advanced pretreatment may also be needed.

THE BOTTOM LINE

Not every vacation home rental is the same, so during the design process we must discuss with the owner how the property will be used and discuss how those decisions will impact the septic system design and longevity. During the design process, the operation and maintenance frequency may need to be adjusted to deal with higher loading and usage issues that may arise for long-term system performance and longevity.