What are the building regulation requirements for installing loft insulation?

The installation or improvement of loft insulation is one of the simplest ways of improving the energy efficiency of a building. Up to 25% of heat lost from a building without any thermal insulation can pass through the roof.

But do building regulations apply to this type of building work?

The building regulations contain requirements for the renovation or replacement of thermal elements - a thermal element is a wall, floor or roof that separates a heated or cooled area from the outside, an unheated part of the same building, or a structure exempt from the building regulations, such as a porch or conservatory. (Further details here.)

This could be, for example, ceiling level loft insulation where you provide, replace, or increase the thickness of the insulation.

These requirements apply where more than 50% of the ceiling area is renovated.

Where there is currently no insulation in the roof space, you will need to provide thermal insulation to achieve a U-value*  of at least 0.16W/m2K. This is typically 250mm of a mineral wool loft insulation roll, for example.

Where there is existing insulation achieving a U-value worse than 0.35W/m2K (approximately 125mm of a mineral wool loft roll) you will again need to provide replacement or additional insulation to achieve a U-value of at least 0.16W/m2K.

There is no need to notify the local authority or gain approval under the building regulations if the insulation of the loft at ceiling level has not been required for specific reasons elsewhere in the regulations.

Irrespective of whether the work is notified or not, the local authority does retain powers to make the builder or building owner address any non-compliance of the building regulations. The sale of a property can also be disrupted if the level of thermal insulation performance is questioned as part of a building survey.

If converting a loft space, remember to consider how you will protect electrical and water services within the it.

Further information

View further information on loft conversions on the LABC Front Door website.

* U-value is a measure of how much heat is lost through a given thickness of a particular material – the lower the value the better.

** W/m2K - watts per metre squared per degree kelvin (the kelvin is a unit of temperature).

Please Note: Every care was taken to ensure the information was correct at the time of publication. Any written guidance provided does not replace the user’s professional judgement. It is the responsibility of the dutyholder or person carrying out the work to ensure compliance with relevant building regulations or applicable technical standards.

^{This article was update on 28 March 2022}