concrete patio over septic tank

[Mike45]

The house is new construction. the septic tank is a black plastic type and has a brick extention collar around the opening because it is below grade. i want a patio above it. it requires more fill above it to bring it up to the level of the house.

Im concerned about weight on the tank and the surrounding pipes. the builder doesnt think there is a problem.

advice?

[Crossy]

Fill the tank with water if it's not already full of something else, weight won't be an issue.

The problem we've seen with pipes in relatively new fill is differential movement as the fill compacts over time. This could indeed damage the pipes although PVC is pretty resilient, concrete less so.

Does your builder intend piling the patio? The piles will take the weight, but then the fill will shrink away underneath leaving a void.

How much extra fill is needed, would an American style deck (in wood or one of the substitutes) be more appropriate than a concrete patio?

[Mike45]

its more than a patio. its an outside roofed room. this picture should help.

Edited June 23, 2014 by Mike45

[eyecatcher]

Inadequate compaction is the reason you see many failed slabs and water pipes, drains.

You don't often see a wacker plate here.

I would just add to crossys advice and say please ensure the concrete slab is reinforced with mesh, a but of extra insurance incase everything decides to settle further.

Also offers protection against pipes shearing.

You say its an indoor room outside? Make sure you have an excellent seal on the manhole lid, ideally triple seal and screwed down otherwise the smell will be truly sickening.

[Naam]

and if something goes wrong with the septic tank or its piping you will have big fun breaking concrete.

p.s. a combination of expat planning and Thai engineering at its best

Edited June 23, 2014 by Naam

[wayned]

Most of the Thai houses built in Bangkok have a septic tank clean out cover , usually in the bathroom. Guess what the entire slab for the house has been built over the septic tank and plumbing. I've had my townhouse for over 16 years, the tank access is in the bathroom, and it has never been pumped even after the 2011 floods when I had 170cm of water in the house. As long as you put in footings and the slab is properly connected to them and the footings for your house you should have no problem.

[Mike45]

and if something goes wrong with the septic tank or its piping you will have big fun breaking concrete.

p.s. a combination of expat planning and Thai engineering at its best

Naam

It certainly looks like it but it wasn't. Truthfully the room wasn't supposed to wrap around that side of the house. I've got a fixed price contract for the addition and the builder just made it bigger than I contracted for.

I'm torn between making it smaller which would mean not being on that side of the house so no interference with the septic and just accepting the larger covered area.

The pipes..... Yeah I agree. I've been complaining about them since they were put in. I'm told that's how they do it. If they break I'll have them relocated into the house wall....probably.

[bankruatsteve]

Make sure it's a true septic tank (with leach field). If you cover a cesspit and no way to access, you will regret.

[JesseFrank]

its more than a patio. its an outside roofed room. this picture should help.

Mike, forgive my ignorance, but the blue pipe at the right side of the brick collar is the pipe that goes from the toilet to the septic tank, right ?

It looks to me as a 2" pipe. Don't you thing that's a bit small for such a pipe ?

[wayned]

The 2" pipe is most likely the "gray water" (shower, sink,etc.) drain and most likely goes directly into a surface drain or khlond as mine does in bangkok. Only the 4" toilet drains do into the septic tank.

[Naam]

and if something goes wrong with the septic tank or its piping you will have big fun breaking concrete.

p.s. a combination of expat planning and Thai engineering at its best

Naam

It certainly looks like it but it wasn't. Truthfully the room wasn't supposed to wrap around that side of the house. I've got a fixed price contract for the addition and the builder just made it bigger than I contracted for.

I'm torn between making it smaller which would mean not being on that side of the house so no interference with the septic and just accepting the larger covered area.

The pipes..... Yeah I agree. I've been complaining about them since they were put in. I'm told that's how they do it. If they break I'll have them relocated into the house wall....probably.

i side and feel with you because i was told the same when i built

[Mike45]

The 2" pipe is most likely the "gray water" (shower, sink,etc.) drain and most likely goes directly into a surface drain or khlond as mine does in bangkok. Only the 4" toilet drains do into the septic tank.

Yes that's my understanding as well.