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Overheating: what’s the difference between the detailed and simplified method?


In June 2022 overheating was taken out of Part L of the England Building Regulations and given its own document: Part O.

As part of the changes, now every new build property must have an overheating assessment to prove that the risk of overheating has been mitigated.

There are two ways of doing this: the simplified and the detailed method. But what’s the difference and which one should you use and when?

Complete Overheating Training


The simplified method

The simplified method was developed by the Ministry of Housing Communities and Local Government (MHCLG). As indicated by the name, it is a ‘simpler’ method than the detailed because it does not involve using Dynamic Thermal Modelling (DTM).

This method would be more suited to buildings which are not located in large cities, due to the urban heat island effect, and where there is cross-ventilation.

It focuses on using measures that are the lowest cost, whilst avoiding the use of air conditioning. It is definitely more prescriptive than the detailed method and dictates what you must do in order to pass – there is no design flexibility.

The detailed method

There are many reasons why you might choose to use the detailed method instead of the simplified method, such as:

  • To get more design flexibility
  • Save money on the building design
  • Or because a building has failed using the simplified method.

The detailed method utilises dynamic thermal analysis using software such as DesignBuilder or IES. It takes into account more aspects that the simplified, and has more inputs, which is why it provides more design flexibility. The detailed method can take into accounts factors that the simplified method can not, including the g-value of the glass and shading from reveals and overhangs

However the detailed method is more costly than the simplified method, requiring assessors to purchase weather data sets and either DesignBuilder or IES software.

Which method should I choose?

There are going to be instances where assessors are forced down the detailed route, purely because their buildings fail to comply using the simplified method. The detailed route will also provide you with more design flexibility and could save your clients money when it comes to installing energy efficiency measures.

That being said, there is still a place for the simplified method, provided it is used for buildings where there is a low chance of overheating.

Interested in providing overheating risk assessments?

Overheating is a financially rewarding area of work that can be completed alongside your SAP work.

Elmhurst runs IES and DesignBuilder overheating training courses throughout the year, which can be booked on the training calendar. There is also the option to complete pre-course software training for those with no experience using IES or DesignBuilder.