Insulated Foundation

Why it matters

The lower junction is one of the places where builders often lose the logic of the envelope. A wall U-value table looks strong on paper, but the wall-to-foundation detail determines whether the thermal layer is continuous in reality. A passive building does not tolerate weak base details because they become permanent, hidden losses.

What the client feels

A better foundation detail is not visible after completion, but it changes comfort. Floors are less cold near external walls, interior humidity risks are easier to control, heating demand is lower and the building becomes more stable during periods of reduced heating or electricity interruptions.

Structural role

The foundation must carry reinforced concrete wall loads, floors, roof loads and local ground conditions. It should be engineered as part of the building, not copied as a generic detail. In rocky, sloped or difficult-access sites, this decision also affects construction logistics and concrete delivery strategy.

Thermal role

Ground-contact heat loss is calculated differently from wall heat loss. That is why the base needs its own detail: slab edge insulation, perimeter insulation, moisture protection and a protected line for the vertical insulation layer.

Airtightness role

Airtightness must start at the base. If the envelope is treated only as a wall property, service penetrations, slab edges and plinth transitions become uncontrolled leakage zones. The foundation plan should show where the air-control layer begins and how it connects to the wall.

Buildability role

The advantage of Passive House Block is that a wall can be built efficiently, but the system still needs a clean starting geometry. A level, accurate, protected base reduces corrections, saves time and makes the first wall course a technical asset rather than a fight on site.

Use as article blocks

• Insulated slab or engineered foundation appropriate to soil and building loads.
• Continuous perimeter insulation at slab edge and plinth.
• Thermal bridge review at wall-to-foundation junction.
• Moisture and capillary protection coordinated with insulation.
• Clear start point for airtightness strategy.

Do not overpromise

Do not claim one universal foundation detail for every country or plot. A passive-house-oriented foundation must be adapted to soil, seismic requirements, groundwater, frost depth, slope, local code and structural engineer input.

Client explanation

It is more convincing to explain the foundation as a risk-control layer than as an expensive hidden upgrade. The client pays once for a base that protects the building for decades; fixing thermal or moisture mistakes later is far more expensive.

Technical anchor

Wall thermal resistance and ground heat transfer should not be mixed into one simplified number. The wall is normally assessed by wall build-up calculations, while ground-contact elements require separate heat-transfer logic.