After excavating and securing the rear bank, we had to start putting in drainage and pipes to remove radon gas from the foundations. There will be a pump that pushes water up to the level of the common to reach the drains on the road.

We have been fortunate to have very little rain — the last thing you want when building foundations.

Now we are building a polystyrene tray which will act as an insulating base for the ground floor. It is pretty much the same material you get when you buy food at a festival in a tray — even so, when we got quoted for building the tray, the market value was £26,0000. We have done it for £8,000 by buying directly from the British manufacturer.

Most of this is now in the ground, but there are still a few piles of it around for the back walls. Pretty much everywhere where the building touches the ground, there will be a foot of polystyrene, so very little heat loss or cold bridging.

In the middle is a ‘toe’ or downstand which will have reinforcing metal in it to resist the pressure of water from the back wall of the building. These will act like anchors to secure the building against such hydrostatic force.

We have already put all of the soil pipes in place in the foundations, for bathrooms, the kitchen and utility. The polystyrene has been built around this. The stairwell has a special carbon activated polystyrene, which is high performance as we needed a thinner product in this part of the floor.

Our finished floor will be 275mm of reinforced concrete floor slab power floated on top of this.

  • Lesley Ash

    How do I raise a ground floor section of floor about 40 cm to match the rest of the house. It has already been insulated. Do I have to put another sandwich of oversite on top of the existing one or just fill it up with rubble and cap it?

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