The whole house is one idea, executed carefully.

01The shell

One pour, no seams, no membrane.

Walls and roof are cast as a single continuous piece of waterproof concrete. The concrete itself is the waterproofing, so there is no separate foil against water and no separate film against radon.

That matters for two reasons. The membrane is the most common long-term failure point in underground building, and a leak below ground is not a repair, it is an excavation. Leaving the membrane out also takes around 30,000 euros out of the build.

The concrete carries a crystalline admixture, so when a hairline crack forms, the material grows crystals on contact with water and closes it. Construction joints are sealed with bentonite, which swells the same way. And because the mix is tuned to the actual weather on the day of the pour, it cures without cracking.

Radon is handled by measurement and by the airtight concrete body, not by a film that ages and tears.

• No waterproofing membrane
• Around 30,000 € saved
• Radon-tight without a film

The first two years were a little humid, like any new build. Now it holds around 50 percent and stays stable.

Talpa House owner

02Earth

The ground does the heating and the cooling.

The soil around and above the house is not cover. It is a battery that stores months of solar heat.

In summer it holds the inside at 21 to 24 degrees with no air conditioning, and at 24 to 25 even when it is 40 outside. In winter it does not fall below 15 to 18 degrees inside, with no heating at all.

Because the earth carries so much of the load, we use roughly half the insulation a conventional passive house needs: about 40 percent less material and less embodied carbon on every build.

The same mass that stores the heat is what makes the house quiet. Most of the walls and the whole roof sit under earth, and the sound of the road stays outside with them.

• 21–24 °C all year
• About 40 % less insulation
• About 90 heating days

We are builders, not furriers.

Martin Pribila · founder and structural engineer

03The roof

The land you build on comes back on the roof.

A house takes a piece of ground out of the world. A green roof gives most of it back, as meadow, as vegetable beds, or as a garden with trees in a deeper layer of soil.

It holds up to 40 cubic metres of rain on your own plot instead of sending it into the public drains, which more and more authorities now require rather than merely prefer. It shades the concrete from the summer sun and buffers it against frost, so the shell spends its whole life at a mild temperature. And because it is soil rather than a covering, there is no roof material to ever replace.

• Up to 40 m³ of rain held on your plot
• Meadow or garden
• Nothing to re-cover

A

Meadow: 8 to 15 cm of soil, sedum and grasses, no watering, nothing to maintain.

B

Garden: 40 cm of soil and more, beds and small trees, watered from the house's own water.

04Light

Light that reaches the back of the house.

The layout follows Socrates' Megaron, refined. Living spaces sit at the front behind full-height south glass. The ceiling is higher at the front and lower at the back, which throws daylight 6 to 8 metres deep, strongest in the morning and the evening, when you are actually home.

A covered terrace shades the high summer sun and lets the low winter sun pour straight in. Skylights and light wells, at least 80 by 80 centimetres, bring daylight down to the back rooms. Every habitable room is checked against the local daylight rule, room by room, which is the part of an underground permit that actually decides it.

There are no windows on the north side, because a north window loses energy and gives back very little light. Leaving it out is not a compromise. It is the reason the south side can be as generous as it is. One of our homes has a single south window 17.5 metres long.

• 6–8 m of daylight into the house
• Skylights from 80 × 80 cm
• No north windows

There is often more light in the living room than we actually need.

Talpa House owner

VI

Summer: the terrace stops the high sun

XII

Winter: the low sun reaches deep inside

05Air

Fresh air without a machine.

Air enters through the windows and micro-ventilation, moves through the house, and leaves through pipes at the rear of the roof by the chimney effect. No fan, no electricity.

A conventional passive house leans on a heat-recovery unit. We do not use one, because the mass of earth around the house does the tempering that the machine exists to do.

Because the air keeps moving, there is no condensation, even where the insulation is lighter than in a conventional build. Humidity holds between 45 and 65 percent all year, and radon and CO2 leave with the air rather than building up.

Where a local code insists on a mechanical unit, we fit one. It changes almost nothing about how the house works.

• 45–65 % humidity
• No electricity
• Nothing to service

06Water

A house that keeps its own water.

Rain filters slowly through the roof soil, a journey of about 24 hours, and collects in a layer of 3 to 7 cubic metres beneath the house.

From there it passes, together with the household's waste water, through a root-zone treatment bed that removes about 99 percent of impurities. Plants and gravel do the work that a treatment plant would otherwise do with pumps and power.

The cleaned water irrigates the roof garden and can serve the washing machine and the toilets. Roughly 90 percent of the water returns to the ground, and only about 10 percent is truly used up.

The rain stays on your land, which is exactly what more and more municipalities now require rather than encourage.

• 24 hours through the soil
• 99 % cleaned
• 90 % back to the ground