It depends on whether the addition includes a bedroom. The Florida Department of Health, which regulates septic systems, specifies the minimum septic tank and drainfield size for construction of a new home based on a combination of the number of bedrooms in a home and square footage of living area. A bedroom added later as part of a home addition means more occupants of the home and more sewage flow, and will likely require installation of a larger drainfield and possibly septic tank, depending on the size of the tank in place before the addition. But an addition or remodeling that does not add a bedroom (which is defined as a room with a closet) does not count in their computation of requirements.

   According to State of Florida Department of Health, Chapter 64E-6, Florida Administrative Code Standards for Onsite Sewage Treatment and Disposal Systems, “a modification, replacement, or upgrade of an onsite sewage treatment and disposal system is not required for a remodeling addition if a bedroom is not added.”

   However, keep in mind that the system was designed to handle sewage needs at the time the home was originally constructed. If the number of occupants or rate of sewage flow increases, you are going to want to upgrade your septic system anyway—to avoid a drainfield failure and stinky backup of the septic tank into your home.

   The minimum size septic tank for a new house is 900 gallons, and is sufficient for a one, two or three-bedroom home up to 2,250 square feet. A four-bedroom home up to 3,300 square feet requires a 1050 gallon size. And, after that, an additional bedroom or 750 more square feet would require a jump to the next size tank of 1200 gallons, then 1350, 1500, and on up.

   For more information about home septic systems in Florida, we suggest clicking the link below to download the report “Your Home Septic System,” by the University of Florida IFAS Extension, below.

YourHomeSeptic.pdf

    Also, see our blog posts Can a house have more than one septic tank? and What are the building code requirements for gray water reuse in Florida?
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  To learn more about septic tank systems, see these other blog posts:

• What can I add to my septic tank to help it work better? 

• Why do septic tank contractors want you to get rid of your kitchen disposal?

• How can I tell if a house is connected to a septic tank system or sewer? 

• How can I locate my septic tank? 

• Does a septic tank have to be re-certified if a house has been vacant for a while?

• What is a grinder pump? 

• How often should I pump out the septic tank? 

• Should I call a plumber or septic tank contractor when my septic tank backs up into the house? 

• Where is the septic tank? Are you going to inspect it? 

• What is the difference between gray water and black water in the plumbing code? 

• Is it alright to disconnect the washing machine drain from the septic tank and divert it to the ground in the yard?

    Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.