Design Builder is specifically designed for exploring options at early stages of design in particular effects of glazing and thermal mass. It uses local weather files to simulate the energy flows within a building over a year, including solar gain.

It is generally used for:

  • Optimising solar gain and minimising heating costs
  • Exploring the effects of different insulation and glazing specifications
  • Exploring the effects of thermal mass for heat storage and cooling
  • Investigating shading design to prevent overheating in the summer
  • Design of natural and mechanical ventilation strategies for cooling
  • Looking at shading at different times of day including from other buildings
  • Modelling underfloor and other types of heating systems
  • Predicting internal temperatures and other comfort information


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This software uses the internationally recognised Energy Plus algorithm and has been tested to ASHRAE 140 – Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs. As such it can be used for modelling required for the Green Star rating system.

Using the model it is easy to find the dimensions of the roof extensions that provide shading to the north facing glazed areas in summer but allow full solar gain in the winter. An annual simulation can be run to examine the effect on heating in the winter and internal temperatures in the summer.

The house in winter – gets full solar gain

And in summer is completely shaded