Marin County’s strategy for affordable housing hinges on encouraging homeowners to build accessory dwelling units. But in West Marin, where most homes rely on septic systems, the necessary sewage upgrades can be cost prohibitive. Now, the county’s Community Development Agency is taking steps to ease that burden. A new pilot program will provide a small number of homeowners who want to build ADUs in unincorporated parts of the county with wastewater engineer consultants who will design the necessary upgrades for their septic systems. The program will also waive permitting fees. Most systems need to be upgraded to accommodate an additional unit on the property. “When you’re talking about building new housing, septic is a limiting factor for both ADUs and infill development in general,” said county planner Jillian Nameth Zeiger. The county has already received a handful of applications for the funds, which come from a state planning grant under S.B. 2, California’s Building Homes and Jobs Act. Ms. Zeiger estimated there is enough money to assist with septic upgrades for about 10 new ADUs. Units offered at an affordable rate will be given preference, and design drawings for the upgrades will be completed within six months. Though the design assistance and fee waivers will help homeowners, the pilot program won’t fund construction of the system or the ADU itself. “I don’t want to sugarcoat it: construction isn’t going to be cheap,” Ms. Zeiger said. “But we don’t have the funds to subsidize construction right now.” The county’s strategy to promote affordable housing in a region with strict zoning and land use limitations has been focused on infill development, especially ADUs. In May, supervisors extended the waiver on permitting and building fees for new separate residential units until 2023. Last year, the county waived fees for 36 new ADUs. Ms. Zeiger admitted that these units best serve a “young person in the workforce,” and aren’t ideal for families. That need remains in rural Marin. Earlier this year, the county partnered with the Bolinas Community Land Trust for a pilot project to upgrade septic systems on the Big Mesa, where the groundwater table is especially high. The upgrades will ensure water safety while enabling homeowners to build ADUs. The land trust also aims to provide loans to finance the construction of the septic upgrades, going a step further than the county’s S.B. 2 project. Both the Bolinas program and the new pilot project will serve the dual purpose of encouraging affordable housing and bringing more septic systems up to code, said Gwen Baert, a county environmental specialist. Today’s creative septic systems function like treatment plants for each property, but the more creative the system, the higher the cost. “We’re doing the right thing by the environment by asking for these kinds of improvements,” Ms. Baert said, adding: “It’s that interplay between the necessity for affordable housing and a clean environment.”