One of the most crucial factors when considering purchasing a lot is whether it’s approved for an on-site septic system.  If not, bottom line, the lot is unbuildable, and you’ve purchased what we refer to as a “glorified strawberry patch”.  But today, it goes far beyond just being perc approved or not. 

In the past, land was much more likely to either get a green light or not. The soil’s ability to filter, e.g. not too sandy or too much clay, was the primary determinant, simply effecting the size of the drain field. Otherwise, there wasn’t much variation in the cost of the system. Today it is a different story, and “perc approved” no longer means by itself a lot approved for a conventional septic system. And that can mean a difference of tens of thousands of dollars.

Conventional, gravity-fed septic systems vs advanced/engineered

If the soil has good filtration and the system is able to be placed on the lot at a point lower than the home’s plumbing system, it will likely be approved for a conventional gravity-fed septic system – the best case scenario. This means you have a septic tank to collect solid waste and a drain field to disperse liquid waste. The drain field is simply a network of perforated pipes placed over a bed of gravel and sand. In 2024, the typical cost of this style of system in southwestern Virginia, is about $9000.

If you’re not approved for a conventional septic system, that will mean something more complex and expensive. These types of systems are known as advanced or engineered septic systems. They can range from simply having a pump to requiring a sand mound for keeping the waste away from the water table to requiring biofilters or aerobic treatment units (ATUs). While we won’t go into detail here about all the different types of advanced septic systems, the key take-away is that they are much more expensive, ranging anywhere from $15,000 to $35,000 plus on average, and require much more maintenance.

Get the details

A difference of $25,000 for an engineered system, or even just an additional $6000 for a pump system can have a material effect on your building budget. We always recommend that before you purchase a lot, get as much information as possible related to the type of septic system that can be used on the lot. If the seller says it’s “perc approved”, be sure to ask for more details about what exactly that means. And of course, the price of the land should accurately reflect the cost it will take to get it “ready to build on”.

Put contingencies in your offer

Even if you’re looking in an area where lots are scarce and you want to lock in a property with an offer, we always recommend putting contingencies related to the septic system into the offer, specifically that the lot be approved for a standard 3-bedroom gravity-fed system. That way should the lot require a pump or an engineered system, you’ll have the opportunity to get the it priced and can decide if you’re willing or able to bear the additional cost of the system and still build the home you want. It could also give you the opportunity to renegotiate the purchase price, if the cost of the septic system is considerably more than anticipated.

Reach out to your builder

If you’re considering purchasing a land or have already purchased some, reach out to your builder. Some, including us, will provide a free assessment of all the conditions on the lot that could affect your cost of building and can help you with estimates on costs. This information can help ensure you put in an appropriate offer or know to pass and not end up with that “glorified strawberry patch”. Always get the details on the septic system and don’t assume “perc approved” means everything’s good to go!

About Ellis Custom Homes

Ellis Custom Homes is one of Smith Mountain Lake’s most trusted builders. If you’re planning to build in the area, contact us and we’ll be glad to meet your lot, or a lot you’re thinking of buying, and provide a free, accurate assessment of the lot and anything on it that could affect your cost of building.

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