Septic system size - what determines it? Can it be upgraded?

[rslaback]

My wife and I are looking to buy a new home. The septic inspection just came back for the one we plan to close on in 23 days. Apparently the septic is only a 3 bedroom while the house is 4. This isn't a huge problem as we are only a family of 5 anyway but I like knowing that I'll be able to sell the home as 4 bedroom when the time comes. Plus, our second choice has the same problem anyway.

So, some questions for the braintrust:

1. Generally speaking, does the septic system get installed based on the house plan or whatever the land will support?

2. The house perced to a convential system so the drainage must be pretty good. The leachfield is also dry so it is draining properly (family of 4 lives there now). Is it possible to add on to the existing system?

3. If the existing system can be added onto does that mean more leach field, larger tank? Both? Convert to a mound system?

I really don't think this is going to prevent us from buying the house but I want to know what I am getting myself into.

 

[Jinks]

Talk to your county permit office, they will have the info you need. Here in Fla. the size of the septic is based on number of bedrooms. They don't care how long you have to wait for the bathroom, just how many are going to use it. They also don't care how many of you there are now, but how many "could" live in the house.

 

[csp]

Number of bedrooms also dictates size of the system here as well.

The best advice is definitely to talk to the jurisdiction that covers septic systems.

Usually it is possible to add on to an existing system, but that determination will be case by case.

 

[Leaflessshadetree]

When I had mine put in the tank size was based mainly on the number of bedrooms (number of bathrooms, sinks etc can be a factor that may determine going to a larger size).
Leach field size and layout was based on soil conditions (how quickly it absorbed water).
I've never heard of adding on to either one, but it could be possible. Also it would be possible to add a second system.

 

[larry_g]

Here in this country tank size is determined by bedroom count. A couple of things come to mind here. 1. What has changed to arrive at this problem. 2. Has an unpermitted bedroom been added? 3. Have the rules changed on septic size since the system was installed? 4. Is the listing agent calling a small office a bedroom to justify a higher listing price?

I agree with the above poster to check with county permits office to make sure that you are not taking on something that is going to bite you. What you have may be perfectly fine and the rules have changed since the house was built and the septic installed. Your septic inspector may only know current rules and not know what was acceptable in the past.

lg
no neat sig line

 

[Lippyp]

Over here theres a formula that takes number of bedrooms and then adds an extra couple of people, so a five bed house has to be able to cope with seven people at a set number of litres per day consumption. In the past though people often skimped on tank size hoping it would be all right.

I say live with it and see if it works for you, if it doesn't cope then its time to dig it up and replace with a bigger tank etc.

 

[Highbeam]

The tank size is pretty standard, 1000 gallons, bigger is always better of course. The drainfield is sized based on how much effluent is coming to it and how fast the dirt can absorb it. So both the number of bedrooms and site conditions. Changing the number of bedrooms increases the effluent that must be absorbed per day so your system will be undersized and fail leading to a health hazard. I added a bedroom to my home without upsizing the septic, however, one of my old bedrooms will be an office for the sale even if that means I have to tear out a closet.

 

[volleyball]

You cannot expand the concrete tank, you just replace it. You can expand your leach field if you need to.
But the system is grandfathered in. So unless it fails, you are good to go. And with the number of people you have, that equals a typical 3 bedroom load.
How big is the tank? Today they would typically be 1000 gal. Do you know the pumping history? Find out. If it has been neglected, you may have to put in a new system.
If this is your first septic, learn how to not damage it. No garbage disposer, limit the harsh cleaners, and such and you should be good to go.

 

[barks]

Be careful. Old systems may have to be completely replaced if anything is done by way of extending life, upsizing or major repairs. As previously mentioned, talk to the permitting authority for the real scoop.

 

[turbowoodworker]

I have limited but fairly up to date information and knowledge on this. most important it varies from state to state and even between counties.
Here in NC, a preliminary septic survey and permit is performed before the building permit can even be filed.
The County Health and septic engineers identify the leach fields that will perc and based on the available field size, the size of the home is then determined. In other words, it is backwards from what others have mentioned. The septic permit determines the number of bedrooms. And unless you can find more field that percs, you cannot add bedrooms.
All this before a building permit is issued.
Ask me how I found this out.
I'm not sure of the ramifications for the OP where his house is built/occupied and the septic system is undersized by septic "code". But I would be very concerned about resale. Much like adding square footage without a permit.

 

[turbowoodworker]

BTW, I had a preliminary permit from the original developer that expired before I started my build. (They were issued for 10 years I think). And when a new permit was requested, the State had changed requirements and the new permit required new surveys and therefore new money. Had to work with both the state and county. PITA.

 

[mcbrideluo]

The best advice is definitely to talk to the jurisdiction that covers septic systems.

 

[larry4406]

Turbowoodworker's experience matches mine here in VA/MD.

The soils capability and field size determine the absorption capacity and thus the rating. This then sets the number of bedrooms. The health departments determine the gallons per day per bedroom. Typically, the health department assumes one occupant per bedroom with a generation per occupant of 150 gpd. So a 4 bedroom house would be sized for 600 gpd.

If the soils are poor and the lot very small, the rating will be low. A larger lot will allow a larger field (even with poor soils) and the rating can be increased.

Increasing capacity typically is done by adding additional leach lines. Sometimes the health department will want a large tank to improve solids settling out with the larger flows. Given that tank sizes are limited by manufacturers, a 3BR system often has the same tank as would be specified for a 4 BR system.

Realtors and home sellers often misrepresent the number of bedrooms in an attempt to increase home sale price. The health department septic permit and operations permit is the final verdict. Get this and then negotiate a price reduction due their misrepresentation of the home.

A point not raised is the concept of reserve drainfield. Here in VA/MD before a drainfield is approved, a reserve area must be proven and dedicated in the land records. The reserve is currently 200% in the counties where I work (used to be 100%). What this means is that if you fail your primary field, you still have a 1st repair (100%), and if you then fail that field, you still have a 2nd repair (100%). The reserve area is off-limits to any construction. The reserve areas are of equal capacity to whatever the initial primary field was. So, a 3BR home would be sited with three 3BR fields in this example. Here, the health departments wont let you upgrade a 3br to 4br without also demonstrating the reserve capacities.

 

[volleyball]

You guys are more likely to be in heavy clay soil areas so the regulations. I know I don't have any reserve area to put a new field.
Some places it is common to dig out and remove old soil and bring in fresh stuff. No reserve area needed.

 

[Diesel Dan]

most important it varies from state to state and even between counties.

^^THIS^^

The tank size is pretty standard, 1000 gallons, bigger is always better of course.

No bigger is not always better. There are formulas to determine the proper size tank but not all communities follow that. There is a "turn over" time frame that gives optimal system performance. For example a system generating 350 gal/day will exchange 100% of the fluid in a 1000 gal tank in 3 days and 6 days for a 2000 gal tank. A system with too large of a tank and slow turnover rate will not be as effective.

Our standard is 2000 gallon tanks(generally two 1000 gal tanks).

But the system is grandfathered in. So unless it fails, you are good to go.

Not always the case either.
Where we are at when a house is sold the system has to be inspected. If a system is severely undersized or causing a nuisance it will have to be replaced.

3. If the existing system can be added onto does that mean more leach field, larger tank? Both? Convert to a mound system?

Only your county BOH(health department) can determine this.
Something to consider is that laws can change and in the future upon sale they could force you to upgrade the system to current standards.

 

[Diesel Dan]

You guys are more likely to be in heavy clay soil areas so the regulations. I know I don't have any reserve area to put a new field.

They may not have a reserve area set aside if the construction predated reserve areas.

Some places it is common to dig out and remove old soil and bring in fresh stuff. No reserve area needed.

I WISH!
Our clay is so bad but we can not disturb the nature soil, regardless.

When we were in WI our house and septic sat on sandy well drained soil while hour neighbors were on clay.

 

[volleyball]

How do you put in drain field if you cannot disturb natures soil? Any field would disturb the existing soil.
And the dig out and replace does not predate the reserve.

And all information is relative, relative to about 20 miles from where you are. Asking the locality is the only way, but getting some info here does give you enough to ask educated questions and to understand the answers.

If the house is old enough, I'd find out if it is a modern septic as opposed to a cesspool.

 

[Diesel Dan]

How do you put in drain field if you cannot disturb natures soil? Any field would disturb the existing soil.
And the dig out and replace does not predate the reserve.

IF you are allow leach lines the only soil you can disturb is for the leach line(trench) itself. If it is a mound the topsoil can not be disturbed.

In Michigan I've seen them strip the top soil back for leach fields but that is not allowable here. Our local officials had their hands slapped by the EPA over septic issues and they are taking it out on the residents by limiting our options for septic systems.

And all information is relative, relative to about 20 miles from where you are.

More like site vs site.
On our property in WI I buried a tile for ~100' and went from loose sand to hard clay to rocky ground. It was something else. Dug down 4' in the sandy soil like nothing and 20' away was throwing sparks off the pick axe after 6".

 

[Kevin54]

You guys are more likely to be in heavy clay soil areas so the regulations. I know I don't have any reserve area to put a new field.
Some places it is common to dig out and remove old soil and bring in fresh stuff. No reserve area needed.

Dependent on what area and what state. We're not allowed to do that. We have to have an area large enough to put in a new leach field if things go bad.

I'm just biding my time with ours. This year I have to have the baffle in the tank repaired. I think when the garage build gets started, then I'll tear into the area where the tank is and get the baffle fixed, and get it pumped. The guy that built the house planted a shitload of trees right over the top of the leach bed. I've taken most of the trees out except for two. I removed one large Maple tree and four large Blue Spruce. And I'm not sure how deep our leach field is. I can see the neighbors already this year, and I have yet to see ours, so it must be deep. When we last had our tank pumped, the guy commented that he's never ran across a septic tank as deep as ours. But to my advantage, if I add a bathroom in the garage, I have enough fall to go to the tank.

For a while around here, they were changing the requirements on septic systems and made it so if anyone had to have one replaced, or a new one go in, it was going to have to be a mound system. It was repealed about a year later. The new houses down the road from me have a fairly high water table, so they had to have a mound system. A huge horseshoe mound out in the backyard. I was talking to the guy putting them in and asked what the price was of a mound system over a conventional system. A conventional system is around $5000 complete. A Mound System is right at $20,000. OUCH!!!!

 

[TractorJeff]

In Wisconsin, I definitely agree it is a County by County ruling!
My brother lived 20 miles away from me in a rocky sandy soil good for a Conventional system. After about 10 years, they changed the law in his County that any new construction or failed systems would be Mounds. In my County, I watched a lot of Mounds go in, but it seems as of late that there are a few places going conventional? Or else I am not seeing / paying attention.
My neighbor had issues with his for a while, he looked into it and told me that if his didn't clear up and he was forced, it would have to be a Mound due to our soil having a lot of clay.
NOTE:
If you are buying an older house and find the system isn't up to code for the house, use this as a bargaining chip in the Sale. A guy down in Indiana bought a house and the system was borderline fail unknown to him at the time of sale. It cropped up when they moved in. Him and a lawyer went back on the Real Estate company and the original owners to make them pay for at least half. He won the case and they paid for half!
Know your local rules!

 

[volleyball]

What is deep, mine is several feet down. I know my entire system. Every inch. Was a lot of work finding out.
I did have a broken baffle. Luckily the local supplier had spare baffles. Just lift out and put new one in hole.
I suggest taking pictures of all that was visible along with landmarks for yours or any future owners benefit.

 

[Diesel Dan]

My WI tank was about 6' below grade.

Not sure how deep I will be going with current house but the discharge line goes below the footers of the house.

 

[Kevin54]

What is deep, mine is several feet down. I know my entire system. Every inch. Was a lot of work finding out.
I did have a broken baffle. Luckily the local supplier had spare baffles. Just lift out and put new one in hole.
I suggest taking pictures of all that was visible along with landmarks for yours or any future owners benefit.

My WI tank was about 6' below grade.

Not sure how deep I will be going with current house but the discharge line goes below the footers of the house.

Our baffles on out tanks are a concrete square. It keeps any floating debris from entering the leach tiles. The concrete will break off and exposes the hole for the start of the leach tiles. So what they do to replace it is to put a PVC "T" in the place of the concrete.

As far as depth, my tank is maybe 5' down, and according to the guy cleaning the septic tank, he told me that 3' is about the norm for tanks.

 

[volleyball]

The cover is concrete but my baffle is metal, just like the original. If anyone wants to check it out, it is still on the bottom of the tank.

I think 1 foot down is typical in my area. Some people use tiles to surround the opening and cap it off so they don't have to dig. These same people flush way too much wrong stuff and have to pump yearly

 

[cleveman]

Whatever you do, don't trust the gov't. We have had three county sanitarians in my years here and I know sanitarians in other counties and they don't always agree on things. We have every opinion from outlawing all septic systems and only allowing sewered properties to the exact opposite. The exact opposite is one guy who likes the idea of the waste generated being processed on the site.

 

[Voi]

1. Generally speaking, does the septic system get installed based on the house plan or whatever the land will support?

2. The house perced to a convential system so the drainage must be pretty good. The leachfield is also dry so it is draining properly (family of 4 lives there now). Is it possible to add on to the existing system?

3. If the existing system can be added onto does that mean more leach field, larger tank? Both? Convert to a mound system?

I'll give you an idea of what myself and some neighbors are going through now after our county septic tank ordinance changed a few years back. Since then every septic system in the county has had to be pumped and inspected. If your tank fails inspection you have a certain amount of time to have it repaired. If it can be repaired you can keep your current tank, even if it's undersized. If it can't be repaired you then you have to replace it with one that meets current size requirements.

As far as sizing, in our area it's number of bedrooms but back when the ordinance was being re-written some of the higher ups were pushing for it to be based on square footage. But it ended up being bedrooms.

Oh yeah, if you have a garbage disposal it increases your capacity requirements by 250 gallons.

Our tank was installed in 1992 and is 1000 gallons. It passed the new ordinance inspection. Our house was originally built as a four bedroom house but we remodeled before the new ordinance and is now five. If we add on over the garage it would be a six bedroom house. Since we have a garbage disposal our tank requirement would be 2250 gallons.

Right now we are grandfathered in since we did all of the work before the ordinance. We only have to upgrade if we add on. Even if we don't add a bedroom during the addition we have to bring the septic up to code just by pulling a building permit.

If we add a 1250 gallon tank it has to go before the current 1000 gallon tank according to code but we don't have enough space between the house and the current tank. We could move the current tank further "downstream" and then add the larger tank but at that point we'd be better off just putting in a whole new system.

Our leach field is dry but we had to have a large profile hole dug for the county to inspect before we even had a percolation test.

Our profile hole "passed" but others in our neighborhood "failed" and they are looking at very expensive evapotranspiration septic systems. I assume these people have systems that failed inspection but they may be like us and looking to remodel.

So back to ours, we are now waiting word on the perc test to see if we'll also have to re-size our leach field and possibly even add a pump so our leach field can be run up our hill to meet sizing requirements.

It has been a real pain. If we had added on back when we remodeled we'd be grandfathered in.

 

[66HertzClone]

Our house was built with four bedrooms, the previous owner added a tiny but full bath to the so called "bonus" room above the three car garage. He listed it as an au pair suite when he put it on the market.

We are nearly finished with an addition to the house which added a home office library, the townships Land Use Board required a deed restriction limiting bedroom to four. Any change to that by us or future owners will require a new larger septic system. You might consider looking at town records to see if there was a change to the original structure and if permits were pulled and the septic capacity is correct for as it is today.

 

[LB-1911]

My wife and I are looking to buy a new home. The septic inspection just came back for the one we plan to close on in 23 days. Apparently the septic is only a 3 bedroom while the house is 4. This isn't a huge problem as we are only a family of 5 anyway but I like knowing that I'll be able to sell the home as 4 bedroom when the time comes. Plus, our second choice has the same problem anyway.

So, some questions for the braintrust:

1. Generally speaking, does the septic system get installed based on the house plan or whatever the land will support?

2. The house perced to a convential system so the drainage must be pretty good. The leachfield is also dry so it is draining properly (family of 4 lives there now). Is it possible to add on to the existing system?

3. If the existing system can be added onto does that mean more leach field, larger tank? Both? Convert to a mound system?

I really don't think this is going to prevent us from buying the house but I want to know what I am getting myself into.

Have you made an inquiry with the AHJ yet?

 

[rancherbill]

The septic inspection just came back.....

I am always cynical.

Was the person a real septic inspector? We do not have them here except for the county during construction.

Is he saying it IS too small or that it is too small nowadays.


I would go to your local government and try to get info on the percolation tests that were done and the plan for the system.

 

[Diesel Dan]

My wife and I are looking to buy a new home. The septic inspection just came back for the one we plan to close on in 23 days.

Since you did not buy it yet I'd get the local health department involved and find out exactly where you stand with current codes. Better to find out now than later.