Old septic tank and foundations

[Lincolnshire Ian]

Hi

We have bought a plot with a grotty 1960s refab bungalow that will be demolished (sorry, disassembled, lots of asbestos) and a new house built on it.

We are hoping to move the house on the plot, but this will mean foundations where the old septic tank is located.

We will get a foundation engineer to design the foundations; we've also got lots of trees to contend with, but what about the septic tank?

The demolition teams that have given us quotes favour digging the concrete septic tank out and levelling it with site soil/rubble. I'm obviously concerned that my foundations will run directly over the old, removed septic tank. I suppose another option might be to just fill the septic tank with concrete and build atop it.

What should I be considering here?

TIA

Ian

 

[Bozza]

If it were me I’d have it removed entirely. Otherwise they’d be unable to assess the soil conditions below.  It might expose soakaways or pipes that you didn’t know about, there may have been a house there prior to the 60s house.

 

I wouldn’t risk putting a new house on uncertain foundations.  I doubt any foundations engineer or builder would either.  
 

Don’t underestimate the value of your disassembled 60s house.  Timber, roof tiles, cable etc all has a value even if it’s free for collection on Facebook.  We demoed our property at zero net cost, and probably ended a few ££s up.  Soz if you knew that already.

 

[nod]

Sounds like our previous build We had three tanks One a modern plastic type The other two 6 meter deep concrete rings One was directly under one of the corners of the house and one under the garage Both had to be filled with concrete The third clean hardcore tamed dow in in layers Our SE dismissed doing anything else 

[Conor]

Only person than can answer this correctly is your structural engineer.

 

We came across a well, right along the edge of the foundations. Call to SE. Said to fill with lean mix concrete, she then designed a ground beam to span over. I would not let your demolition contractor tell you what to do. They are, after all, experts at making things fall over, not stand up.