Using 4DFlo to design your building

This online design tool is a dynamic modelling software written by Breathing Buildings. It is free to use because we want to help with the provision of better buildings.

The software has been developed to assess whether a particular design is compliant with the summertime overheating criteria, as laid out in Building Bulletin 101 (BB101).

BB101 was revised in 2017 and the dynamic thermal modelling software 4DFlo is designed to assess the performance of your building against the summertime overheating criteria described in this document.

Weather file selection

Unit selection



Occupancy and internal heat gains

User details


Once you have configured your room, use the 'Calculate' button, to see an analysis of your results. Then check your email for more information on BB101, making your design as efficient as possible and contact details for our dedicated design team.

Please note that our email may have been filtered as spam, be sure to check your junk folder should it not show in your inbox.

Number of hours above acceptable temperature: {{ results.hoursAboveAcceptableTemperature }}

Max weighted exceedance: {{ results.maxWeightedExceedance }}

Number of hours above upper limit temperature: {{ results.hoursAboveUpperLimitTemperature }}

Max temp difference between inside and outside: {{ results.maxTemperatureDifferenceInsideOutside }}

BB101 Result: {{ results.bb101Result }}