Hi there - I could really do with your advice.

I have a house in the caribbean that is about 60 foot long. I have just installed a new septic tank, with 4" pipe running at least 1/8th" of fall running down both sides of the house along its length. These are going to be the main soil pipes from the house to the septic tank - they join together just before the tank with a Y fitting and cleanout and enter the septic tank as one 4" pipe. All good so far!

I am installing 4 ensuite bathrooms and 1 toilet and sink on the ground floor and want to add a second floor with upto an additional 6 ensuite bathrooms.

As the 4" pipes enter the house horizontally, I plan to go vertical first in a cavity wall with Ys and 45's to create 4" drain stacks for the second floor, and then on the ground floor horizontal section to go to 3" to service the toilets, showers and sinks. The 3" dry vent would rise from the toilets up through the ceiling, (with sinks and shower T-ing into it), so on the second floor I will see my 4" vertical drain stacks and then also the 3" vertical dry vents coming up through the floor. Still all good so far.

How do I now connect my second floor toilets to the drainage and vent them? I guess I can't position my 2nd floor toilets directly above my first floor toilets as the 3" dry vent would now become a wet vent and given the number of bathrooms on the second floor (up to 6 in total), I guess I would exceed capacity. I also believe I would need to re-plan the ground floor venting so that it now joined up above the 2nd floor waste connections.

Am I right in thinking I need to go 3" horizontal off the 4" drain stack for my toilets again (as I did for the ground floor), then vent with 3" again and then T the ground floor vent and second floor vents into the 4" drain stack above any drain fittings (so I end up with a 4" dry vent coming out the roof, with the 1st floor and second floor dry vents entering it).

Will this work effectively and are there any other ways of doing this? I want to do this right first time, as I am doing this on a crazy tight budget!

Thanks

Richie

You should have roughed in soil stacks where bathrooms are at to receive discharges from soil and waste pipes. It sounds like u are going to tie the 6 suite bathrooms on 2nd floor with the 4" stack by either dropping the ceilings to make connections or installing a horizontal wet venting which is which used if there is no other way of roughing in your soil and waste connections. also this horizontal wet venting is also used if not all fixtures are used at the same time due to water restricting flow of air thru wet vents. you are only allowed 3 toilets on a horizontal 3" trunk. So u would have to run 4" up to the first 3 toilets, then reduce to 3" to tie in other 3 toilet in 2nd floor.
As for vents because of amount of fixtures u plan of having 3" is minimum for a stack vent to recieve other branches. u could tie in to the vent coming off the main floor vent with 2nd floor vents as long as u are 6" above flood level rim of fixtures and u are within the required length for vents.

'I have a house in the caribbean'
Are you allowed to do all this by local code and zoning, starting with size of septic and adding a second floor?

Sorry - I may not have made my plan quite clear

I will have 3x 4" vertical stacks entering the 2nd floor close to where I plan to have the 2nd floor bathrooms. Each stack will service 2x 2nd floor bathrooms to bring a total of 6 2nd floor bathrooms. The bathrooms will have dry vents to ensure proper function. The 3x 4" stacks will come out vertically from the ground floor (I'm cutting a hole in the ceiling and having the pipe go straight up into the 2nd floor, then encasing the pipe in a cavity wall so you can't see it go through the ceiling)

On the ground floor, (in addition to the 2x 2nd floor bathrooms that each 4" stack services), 1 stack will service 1 bathroom and one toilet, 1 will service 2 bathrooms and the third one will service 1 bathroom.

Thanks for answers so far - please keep them coming. They are much appreciated

First thing I did when I bought the house was to install a commercially sized septic tank to handle the planned increase and allow me to get the pipework done right.

Planning is pretty relaxed here for pre-existing houses. My house didn't even have a vent when I bought it. Neither did my next door neighbour! I can add a second floor when I like - it's the caribbean!

OK... good luck.
Jus wondering cause the Caribbean is 7,000 islands, 13 independent countries, territories of Great Britain, etc. And some aren't so easy going.
Maybe I'm jealous. I live on a lake and can't even add a parking space without permission.

You're right - it does vary a lot. It also depends on who you know and how much you have immersed yourself in the community. If you get involved, then things like plannng become a lot easier!

Some guys down the street just added a second floor to their house over the weekend. They just went to the hardware store, bought a bunch of wood and had that second floor up with the roof on before you knew it! Pretty impressive.

Living on a lake sounds nice, too - even if you can't park where you want!