Suspended Timber Floor Insulation

At the time of writing the methodology for EPC assessments of existing dwellings is RDSAP 9.94. The much anticipated RDSAP 10 update is due in Q1 2025 and a significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed for 2026.

We'll add some further content here soon. For now here is a simulation of the EPC improvement to my house if I had a suspended timber floor and had insulation added:

My house actually has solid floors but if I were to simulate a suspended timber floor in an assessment, and add some insulation, here are the ratings I would achieve:

This is a 1950s terraced house that we cover in our Case Study 2 page.

So the difference for my property is small considering the amount of physical work required and the cost of materials.

The increase from 50mm to 100mm and then 150mm does not result in an integer increase in the EPC rating for my property but it will be making a smaller fractional difference behind the scenes, just unfortunately not enough to be rounded up to the next integer value of 70.

It would be possible to do this type of work as a DIY project but you would need to submit a formal Building Control application with exact details of the materials used so that the documentary evidence could be used by an energy assessor to support the declaration of the insulation in the EPC assessment.

Always contact a local energy assessor and get them to work out what EPC rating improvement you would experience with your own property before proceeding with any works.

A recommendation for Suspended Floor Insulation will be included on an EPC certificate under the following conditions:

• Below the building part there is:
  • Ground or External Air or Unheated Space, and
  • The floor is Suspended

And:

• The Floor is:
  • As Built, age band <=J [ie. prior to 2007 in Eng&Wales] or
  • Has retrofitted insulation <=50mm or
  • Has a U value of > 0.5

The EPC rating indicated on the certificate with this recommendation implemented will have been calculated using:

• Insulated Floor with
  • E&W and NI: U value = 0.25
  • Scotland: U Value = 0.18
  • For a park home, refer to Appendix S1.1.2

Click here to return to our 'Improve Your EPC' main page, and see if there is another way you could improve your EPC rating.