# Add Subfloor
A subfloor is the space beneath your floor system, often raised above the ground and ventilated. While it might seem like just a structural gap, it plays a major role in how your building handles heat loss and moisture. That’s why subfloors are included in Total R-value calculations, following guidance from CIBSE Guide A.
## Floor
To begin setting up a subfloor, click 'Add Subfloor' from the main area of the Floor Designer. Start by filling out the floor conditions.
### **Soil Type**
Start by selecting the Soil Type beneath the floor. Options include:
* Clay (1.5 W/m·K)
* Sand (2.0 or 3.0 W/m·K)
* Rock (3.5 W/m·K)
This value sets the soil’s thermal conductivity, which affects how heat transfers from the floor to the ground.
### Perimeter of Exposed Floor
Set the Perimeter of Exposed Floor to account for ground heat loss calculations.
Choose your floor structure, such as slab-on-ground or suspended.
### Ventilated Cavity
Next, define the air space beneath the floor.
#### **Floor Height Above Ground**
Set in millimetres. This determines whether the space counts as ventilated or not.
#### **Subfloor Ventilation Area**
Enter the area of ventilation openings per metre of perimeter, in m²/m.
#### **Wind Speed**
Provide the average wind speed at 10 m above ground level, which helps determine ventilation rates.
#### **Wind Shielding Factor**
Choose from:
* *Sheltered* – limited wind exposure
* *Average* – typical suburban conditions (default)
* *Exposed* – open terrain with strong winds
These values influence how air moves through the cavity and how effectively it removes heat and moisture.
## Wall
Finally, set the properties of the surrounding walls enclosing the ventilated space.
### **Wall Width**
Total perimeter of walls enclosing the cavity.
### **Wall U-value**
Thermal transmittance of the wall material.
### **Wall Depth into Ground**
How far the wall extends below the ground surface.
These inputs affect the way heat interacts with the ground and the stability of the thermal environment under the building.
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