Cavity Wall Insulation Regulations Guide


Cavity wall insulation is commonplace across a range of properties, both residential and commercial. Not only does cavity wall insulation help us keep warm in cooler months, it also has a knock-on effect on our energy bills. For these reasons, the installation of cavity wall insulation has become a standard procedure for a wide range of construction projects – but it’ s important to install insulation effectively and in accordance to building regulations.

In this blog from Cook Brown, we provide a complete guide to cavity wall insulation regulations, noting what regulations must be met and how support from industry specialists such as Cook Brown Building Control can grant peace of mind when it comes to effective installation.

For more information related to construction compliance, visit our blog – existing articles include What do the new 2023 building regulations mean for building developers and The differences between English and Welsh building regulations.


What is cavity wall insulation?

Cavity wall insulation refers to the insulation material that is installed into the cavity of a building – a cavity being the space between a structure’s inner and outer walls.

Cavity wall insulation comes in a variety of forms and works to keep warm air in and prevent air from circulating around the cavity – leading to a loss of heat. Installing cavity walls has a range of benefits including reduced heat loss, reduced heating bills and greater insulating performance for a property as a whole.

For new buildings and extensions cavity wall insulation is usually made from mineral fibre wool or polyisocyanurate (PIR) sheets.  Some existing homes, usually built between 1940’s-1960’s may have cavity walls without any insulation, in these instances may be possible to add insulation made from mineral fibre wool, polystyrene granules (also known as beads) or polyurethane foam.  Providing insulation to a previously uninsulated cavity wall should be carried out by a specialist contractor.

Speak to a member of the team about your cavity wall insulation project >


What building regulations apply to cavity wall insulation

When it comes to building regulations related to insulation, Part L of the building regulations is of central importance. Part L deals with all matters of thermal performance, such as limiting heat loss. Part L has evolved considerably over the past decade, receiving numerous edits over recent years.

We measure thermal efficiency in terms of “U-Values” and each component of a cavity wall needs to be considered to provide an overall rating for the wall. These figures provide a maximum allowable limit as opposed to a building objective.

The latest update to cavity wall insulation building regulations was provided in June 2023, covering the 22/23 year. This outline is essential information for all builders and homeowners conducting any kind of property building or modification project. In addition, a notable mandate has been announced by The Department for Levelling Up, Housing, and Communities (DLUHC).

Learn more about U Value calculations with our sister company Cook Brown Energy >


How can building inspectors help make cavity wall insulation compliant?

Building inspectors can play a significant role in ensuring a building is compliant with building regulations, including those governing cavity wall insulation. When it comes to installing cavity wall insulation, failing to do so correctly could result in a fine or even prosecution. For this reason, seeking the help of a specialist building inspector such as those at Cook Brown Building Control. We are an alternative to local authority building control and are authorised under the Building Act 1984 to carry out the Building Control function in England and Wales. In addition to working with the Insertion of insulation into cavity walls, Cook Brown’s Registered Building Control Approvers assist in:

  • Erection or extension of a Building
  • Installation or extension of a service or fitting which is controlled under the Building Regulations
  • Undertaking alterations involving work that may affect the compliance of an existing service or fitting, whether temporarily or permanently
  • Underpinning the foundations of a building
  • Undertaking work to thermal elements, energy status or energy performance of a building

As a registered building control approver, we also undertake the issuing of statutory notices, consultations and certification, check drawings, details and calculations for compliance at all stages and undertake regular site inspections over the duration of the project.



Registered Building Control Approver Services from Cook Brown Building Control

At Cook Brown Building Control, we are approved construction inspectors who provide specialist building consultancy services across England and Wales. As specialists in both commercial and residential construction projects, we are committed to supplying high-quality consultancy throughout a range of contexts.

The services available at Cook Brown Building Control help project managers across all stages of a construction project, including effective and compliant cavity insulation installation. By forming a relationship that spans every stage of construction, clients are able to feed back to our industry experts throughout the duration of a project. By having access to this professional advice, customers are able to avoid planning or construction mistakes that could increase the price of their project overall. Looking for support on your next construction project? Get in touch with one of our team or request a quote today.