Hi there, We were thinking of purchasing a home that has a septic for only 3bedrooms.How costly would it be?

Asked by J, Greensboro, NC Fri Feb 27, 2009

to make it into a 4bedroom septic.

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John Gallagh…, , Roanoke, VA
Fri Feb 27, 2009
J, Thanks for the inquiry. I have some experience with septic systems in our sub-division and going from a 3-bedroom septic to a 4-bedroom septic has several dif't costs involved:
1) You would need to have a soil scientist come out and take a test the soil and determine how much larger the septic field needs to be to go from a 3-bedroom to a 4-bedroom. (Cost estimate - $500
2) Depending on the results, you would then need to have an installer come out to install the lines to increase the field size to support a 4-bedroom home. (Cost estimate ranges from $1,000-$10,000, depending on the type of system)

The important things to know prior to doing this are: 1) What type of septic system is already in place (is it gravity, pump back, or a more elaborate system)? If so , the lot may not support additional lines. 2) How many people will be living in the home. Most local health departments size septic systems for 2 adults per bedroom in the house.

SO, there are several questions to answer prior to increasing the size of the septic field. The fact of the matter is that you can elect to leave the home with a 3-bedroom septic and 4 bedrooms without changing anything. But, when you go to re-sell in the future, you must still disclose that you have a 4-bedroom home with a 3-bedroom septic. This may or may not affect the sales price of the home in the future.

A long-winded answer, but a very important question. If you have any further questions, please contact me.
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Emmanuel Sca…, , Collin County, TX
Sat Feb 28, 2009
Hello J.,

The North Carolina Division Of Environmental Health controls the state rules/regulations regarding on site septic systems (OSS). A copy of the state regulations concerning OSS' can be found at:


Septic system are based on a "Gallons Per Day" flow rate/processing capability. NC requires systems to be capable of handling a minimum of 120 gallons per day for each bedroom, or designated sleeping area, with a minimum capability of 240 gallons per day for any OSS. That is based on a typical maximum of two persons in each bedroom. If there are to be more than two persons per bedroom the rates are calculated at 60 GPD per person (i.e. 3 in a bedroom is 180 GPD for that bedroom. It basically works out to 60 GPD per person. In your example a three bedroom home, with 2 in each room, would require a minimum capacity of 360 GPD. Many systems are sized at 500 GPD and larger, although there have been systems smaller than 500 GPD.

The first item of information you would need to know is what the current system is capable of handling/processing. Somewhere near the septic system is generally a tag describing the system and its capabilities. Many times it is gone from aging, etc. The local department of health, either county or city, should have a permit record for the current system and can tell you what its basic capabilities are. Once you know what is there you can then move on to decide if the system is currently of sufficient size to handle your new 4 bedroom requirement.

If your system is not capable of handling the increase in residency the Division Of Environmental Health can point you to lists of licensed individuals and companies that can make the recommended changes. Keep in mind that you should never allow your usage to approach the listed maximum processing capability of the system. For example if you have a system capable of processing 500 GPD and you are moving up to an 8 person occupancy that would require a system processing at least 480 GPD. As you approach the systems maximum capability you risk the very real chance of overloading the system or finding its weaknesses. There are acceptable buffer zones that should be maintained.

Good luck on your purchase.

Emmanuel J. Scanlan
PS Inspection & Property Services LLC
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Vicky Chrisn…, Agent, Purcellvile, VA
Sat Feb 28, 2009
J - do you really have to do this? Generally, a 3 bdrm septic will support a family of 6 full time residents.
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