✅ For Best Experience: This article covers advanced technical stuff. To get the most out of this guide, we recommend starting with our introduction to the topic: Boundary Types Guide.

This category includes floors between stories, balconies, internal walls, and corners.

Intermediate Floors and Balconies:
- Within the same dwelling: The spaces above and below the floor are both at the internal temperature (20°C).
- Between different dwellings: The model boundary is split. Your model would show the internal temperature (red) on your side and an adiabatic boundary (green) representing the neighboring property.
Corners:
- Normal Corner: An external corner where two walls meet. The internal boundary is on the inside corner, and the external boundary is on the outside.
- Inverted Corner: An internal corner. The modeling is reversed, with the external boundary in the corner and the internal boundary on the outer faces of the walls. An inverted corner typically has a negative thermal bridging value, meaning it can offset the heat loss from a normal corner.

New to this guide? If you're just getting started, we suggest reading our Boundary Type Guide first for reference.

How to Model Intermediate Floor

How to Model Balcony

Junction Within the Same Dwelling

When the floor or balcony is entirely within one property, the spaces above and below are at the same internal temperature (Ti).

Boundary Setup: The areas above and below the floor slab are set to the internal boundary condition.
Measurement (lw): The length used for the calculation includes the wall sections above and below the floor, plus the thickness of the floor itself (lw=a+b+c).

Modeling Note: Always include any skirting boards in your drawing

Junction Between Different Dwellings

When a floor or balcony separates your property from a neighbor's, the modeling changes slightly.

Boundary Setup: You only model your side of the junction. The neighboring property is treated as a boundary.
Measurement (lw): The calculation length only includes the wall sections on your side (lw=a+b).

Calculation Note: The resulting thermal bridge value (Ψ-value) is calculated for the entire junction, and half of this value is allocated to your dwelling

How to Model Partition and Party Walls

Internal Partition (Same Dwelling)

This is a wall dividing two rooms within the same property.

Boundary Setup: Both sides of the partition are at the same internal temperature (Ti).
Measurement (lw): The length includes the two adjoining wall sections and the partition's thickness (lw=a+b+c).

Party Wall (Between Dwellings)

This is a wall shared with a neighboring property.

Boundary Setup: Your side is set to the internal temperature (Ti), while the neighbor's side is typically set to an external or unheated temperature (Te).
Measurement (lw): The length includes only the adjoining wall sections on your side (lw=a+b).

Calculation Note: Just like with floors, half of the calculated Ψ-value is allocated to your dwelling.

How to Model Corners

Corners represent a significant area of heat loss and have specific modeling conventions.

Normal Corner (External)

This is a standard outside corner of a building.

Boundary Setup: The inside of the corner is set to the internal temperature (Ti), and the two outer faces are set to the external temperature (Te).
Calculation: The thermal bridge (Ψ-value) is typically a positive number, indicating additional heat loss compared to the flat walls.

Inverted Corner (Internal)

This is an inside corner of a building.

Key Concept: An inverted corner is more thermally efficient than the flat walls connected to it. This means it has a negative Ψ-value.
The "Canceling Out" Effect: In a simple rectangular room, the extra heat loss from the four "normal" external corners is partially offset by the thermal gain from the four "inverted" internal corners. For calculation purposes, this means the net heat loss for a simple enclosed space is equivalent to the effect of four positive corners.