Build Your Own House

I'm trying to decide whether to put in a septic tank and sand filter before the slab is done, or when the house is at lockup stage. We are on a fairly rocky hilltop (sandstone/siltstone) and there is a possibility that a rockbreaker may be needed to dig the holes for the septic tank and sand filter if a reef of rock is struck. We're relying on the slab to keep termites out, as we're not using chemicals. One tradesperson said he'd heard of slabs cracking when a rockbreaker had been used to put in the septic tank after the slab had been done and that it would be better to do the ST first. Another tradesperson thought cracking would be highly unlikely, and that the risk and nuisance value of having to rope off the ST and SF to stop people driving or parking on them and wrecking them would outweigh the risk of a rockbreaker cracking the slab. A council official also pointed out that it would be hard to get the septic tank and its pipes in exactly the right place before the building was done.

Any experience/comments welcome.

Ours isn't a septic (we're installing a worm farm) but we're not installing it until we're close to lock-up.

Why? Well, we're owner builders (naturally) and it could easily take us a year or two to get the project that far, and I don't want a tank and plumbing installed now when we're not likely to use it for a while. There are plenty of reasons - I want to be sure the installers are in business from go to whoa, I want the installation fresh in their minds if anything goes wrong with it, and I want the whole thing to be under warranty. If the job spans many months (or years) then there'll be a sh!tfight getting anything fixed if/when it goes wrong. We do have the pipes in place where there are slab penetrations, but that's all at this point.

On the topic of slabs cracking, I would expect that if the foundations are sound then unless you're excavating/breaking rock very near by, you'd have little to worry about.

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Simon.

The adventures of an owner-builder in the Tallarook Ranges

Thanks Simon. The Septic Tank and Sand Filter are both 3 metres away from the slab.

With the house we're presently in, the tank had to go in first because the trucks involved would not have been able to access the required area once the house was in place. Between fences, trees, shed & the house we've only 1.8m maximum space.

Where we are now building I'm putting in reedbed and installing this early so that it has time for the plants to mature before occupation.

I'm not sure there is a single right answer, but it's going to depend on many individual circumstances.