Country property has a vocabulary all its own. One often confusing term is “perc” or “perc test”. Perc is real estate jargon for “percolation”, a perfectly good word for the ability of soil to absorb moisture. Still, the word percolation manages to baffle people more accustomed to coffee percolation than septic systems. Since percolation is only a confusing word because of context, real estate people create more linguistic chaos by shortening it to “perc”, a word no urban person has a clue about.
Urban dwellers know sewers. They pay bills directly to cover the cost of taking their waste water from toilets, showers, sinks, and laundry to a sewage treatment plant. It’s a more or less invisible process, except for paying the bill. The mystery of what happens to all the waste happily stays a mystery for most people. Like how to do a tune-up on your car or change the oil.
Rural residents, on the other hand, have to act as their own sewer district. There are no sewage treatment plants or complex infrastructure to carry their waste to a distant plant. Instead, country property typically relies on a technology called a “septic system”.
The two key components of this are a septic tank which holds the recent waste and a “leach field” where the liquid components of the waste are allowed to “percolate” into the soil. If the property happens to have rocky or heavy clay soils, the “percolation rate” might be too low to allow for a septic system to be built. In that case, you would literally have an unbuildable lot. It happens. Don’t buy one.
More likely, the soil will have an acceptable percolation rate, a situation that is often referred to as “passing the perc test” or “having a good perc”. There’s a lot of variation in the rate of percolation and in the amount of area available to build a leach field. Those two factors combine to give a property a rating for the number of bedrooms a home can have. It’s very usual to see a property advertised proudly with a four or five bedroom perc. It clearly adds value to the land to be able to support a bigger house or a main house with a guest house. Marginal property (from a perc standpoint) with a two bedroom perc will struggle to attract the same price as nearby property with more septic capability.
So, the next time an agent starts tossing perc test and leach field and expansion field and mound system and standard septic terms around, at least you’ll know that they are talking shit waste.
The Real Deal
- Sonoma County Definition of a Bedroom
- Sonoma County Site Evaluations and Percolation Test Methods (Comprehensive)
- Sonoma County Well and Septic FAQ