I was pondering something way above my home repair grade, so please
tell me if I'm heading in the right direction.
I have a septic system tank and drainfield that uses good old gravity.
I want to add an addition with some bedrooms. I am concerned that I am
perc'd to the max and don't have much room to build a bigger field.
Can I modify my gravity system and upgrade it to a "low pressure
system"? to get more out of my field?
What is really the limiting factor to the number of bedrooms? The
perc? The available field size?
What are some other alternatives to getting those extra bedrooms?
You need to look in the yellow pages under septic systems, then call some
for advice and estimates. If your board of health requires a perk test,
those guys can usually tell you the best place to dig the hole.
The leach field size is heavily dependent on the perc rate/soil type,
as well as nearby streams, ponds, rivers, etc. The size of the field
is usually determined similar to this:
Amount of wastewater capacity needed is determined by a set number of
gallons/day per bedroom - the number will probably vary depending on
where you live
The perc test determines how much wastewater your soil can absorb and
thus how many linear feet of leach line are required per gallon/day.
There are some leach pipes called "infiltrators" that are supposedly
better than the standard round-perforated (ie. more capacity in a
shorter length), but it'd be up to the local official as to if/how
these can be used.
The tank size may need to be upgraded, depending on how large the
current one is and on your local codes.
Many areas now are requiring sand-bed or raised-bed systems be
installed when a new or upgraded system is installed. This can be VERY
expensive in some cases and will take up a fair portion of your
property with a large mound of sand.
All in all, Bob has a good idea about calling some contractors and
getting ideas and even some quotes.
Adding bedrooms... either you need them or you don't. If you need the
extra room and it's not just going to be a convenient spare bedroom,
there isn't much you can do other than make the kids share bedrooms
(like the bunkbed suggestion).
Only your local Board of Health or similar agency can make that
determination. Ask them.
The calculations for designing a septic system assume that every human in
the house uses a certain amount of water per day. It further assumes that
there is one human for every bedroom. The assumed gallons per person factors
in the fact that there is often more than one person in a bedroom.
The perc rate determines how many gallons of water could be drained through
a given area of the soil in your yard in a given amount of time.
The size of the leach field is calculated using the amount of water to be
introduced and how long it takes to drain through the soil. The faster the
water drains, the smaller the area the leach field needs to be, and vice
If you have the room on your lot, you make the leach field larger.
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