What Is a Floor? (vs. a Ceiling)
In building physics and MCS heat loss calculations, a floor is defined as the horizontal building element that forms the bottom surface of a room.
A floor separates a space from what lies below it (ground, outside air, unheated space, or another room).
A ceiling, on the other hand, is the upper surface of a room — essentially the underside of the floor above.
For heat loss calculations, the focus is on floors (since they can lose heat to the ground or to external/unheated areas). Ceilings are only relevant if they act as an exposed element (e.g. top-floor ceiling under an unheated loft).
Types of Floors:
Ground Floor
A ground floor is any floor that sits directly on the ground or above the ground but with soil immediately below it.
Examples:
Concrete slab-on-ground
Suspended timber floor with ventilated void over soil
Basement floor in contact with soil
Exposed Floor
An exposed floor is a floor that separates a heated space from the outside air below.
Examples:
Floor above an open passageway or carport
Floor above an unheated garage or undercroft
Overhanging room (cantilevered floor)
Internal Floor
An internal floor is a floor between two heated spaces within the same thermal envelope.
Examples:
Floor between ground floor and first floor in a heated house
Floor between apartments, where both are heated
Why It Matters for MCS
Correct classification avoids under- or overestimating heat loss.
Misclassifying an internal floor as ground or exposed can inflate heating demand and oversize the heat pump.
Misclassifying an exposed floor as ground can underestimate losses, risking comfort issues and non-compliance.
Proper classification ensures calculations meet BS EN 12831-1:2017 (mandatory for MCS from June 2025).