ISO 13370:2017

Overview

ISO 13370:2017 - "Thermal performance of buildings - Heat transfer via the ground - Calculation methods" provides standardized calculation methods for heat transfer between buildings and the ground. It covers slab‑on‑ground floors, suspended floors and basements, and defines the boundary planes for different cases (inside floor surface for slab‑on‑ground, suspended and unheated basements; external ground surface for heated basements). The standard calculates both the steady‑state (annual average) heat flow and the seasonal (monthly) variations caused by annual temperature cycles.

Key topics and technical requirements

• Calculation methods for heat transfer coefficients and heat flow rates for building elements in contact with the ground.
• Treatment of both steady‑state thermal transmittance and periodic (seasonal) heat flow variations on a monthly basis; shorter time steps are outside the standard except where covered for dynamic simulation (Annex F).
• Definitions of input data and thermal properties: ground and building materials, surface resistances, internal temperatures and climatic data.
• Consideration of thermal bridges (e.g., wall/floor junctions) and methods to include their effect in overall heat loss assessments.
• Parameters such as characteristic floor dimension and equivalent thickness used to simplify ground heat flow modelling.
• Normative and informative annexes addressing specific modelling cases:
  • Annex C: ground heat flow calculation
  • Annex D: slab‑on‑ground with edge insulation
  • Annex F: application to dynamic calculation programs
  • Annex G: ventilation below suspended floors
  • Annex H: periodic heat transfer coefficients

Applications and who uses it

ISO 13370:2017 is intended for practical use in:

• Architects and building designers specifying floor and basement assemblies
• Energy engineers and thermal modelers calculating building energy performance and heat loss to ground
• Regulators and compliance bodies adopting consistent methods for building codes and EPB (energy performance of buildings) assessments
• Construction product manufacturers and consultants evaluating effective thermal resistance and insulation strategies for ground‑contact elements

Typical applications:

• Assessing floor and basement heat losses for energy performance certificates and compliance
• Designing foundation insulation strategies (e.g., edge insulation for slabs)
• Incorporating ground heat transfer into whole‑building energy simulations
• Estimating thermal bridging at floor/wall junctions and impacts on internal surface temperatures

Related standards

• ISO 52000‑1 (EPB modular structure; linkages with output variables)
• ISO 6946 (thermal transmittance for elements exposed to external air)
• ISO 13789 (methods for overall heat loss of buildings)

ISO 13370:2017 is a practical, internationally recognized reference for consistent modelling of ground‑related heat transfer in building energy assessments.