Insulation Building Regulations: A Complete Guide 2025

Home insulation has become a frontline to combat rising energy insecurity and soaring bills in the UK. In line with the ambitious Net Zero by 2050 goal, the UK housing stock is dramatically transitioning towards energy efficiency and sustainability. 

But what rules and regulations govern home insulation? How can you ensure you’re current on what is expected? This complete guide by WhatCost will provide you with the most up-to-date building regulations and insulation demands.

Ready to insulate your home? WhatCost is here to help. Save yourself endless hours of research and vetting by spending just 30 seconds to fill out our online intake form. In return, we’ll send you up to 3 free home-tailored quotes from our nationwide network of trusted professionals. No costs or obligations apply. Simply click below to begin! 

The UK Building Regulations outline a range of requirements for construction safety in both the commercial and residential spheres, with Part L of the documents focusing specifically on insulation measures. 

These measures may differ depending on your home type (e.g. newly built or refurbished), chosen insulation, and the type of job carried out. The best way to ensure you meet requirements is to work with a professional installer who can tailor an approach suited to your budget and needs. 

To get things started, here’s a breakdown of the expected u-values that building regs insulation expects, depending on whether the house is a new build or a renovation of an older property:

The u-value is the rate by which a material can prevent heat transfer. A lower value indicates a better insulation capacity.

The thickness of insulation that is installed is directly proportional to the u-value to be achieved. This means that insulation thickness can vary greatly depending on the material you use. 

For example, 270mm of mineral wool and 120mm of PIR board can achieve the same u-value in many cases, except that you require much less thickness of the latter material. Here’s a summary of the average building regulations insulation thickness you can expect per job.

Wall insulation is most often carried out by the use of mineral wool or other similar blanket-style insulation material. This is because it's easy to install, relatively inexpensive, and sustainable. Here’s a breakdown of what you could expect from internal, external, and cavity wall insulation regulations:

Roof insulation measures are popularly carried out by using mineral wool or similar blanket-style insulation, however, rigid boards such as PIR and EPS polystyrene have become more popular in recent years. Loft insulation regulations tend to follow the same outlines as roof insulation regulations. Here’s a breakdown of the thicknesses you can expect to need as per roof insulation building regs:

Floor insulation helps to cut a further 8-10% of home heat loss. To achieve this, various insulation materials can be used at varying thicknesses depending on the heat retention capacity of the material. Here’s a breakdown of expectations set out by building regs for floor insulation:

Adhering to insulation building regs is crucial for maximising energy efficiency, enhancing home comfort, and ensuring long-term value. Here are key steps to achieve compliance and a successful installation:

Unfortunately, not many prospective customers have endless hours to give to research and vetting, ultimately settling for high prices and low-quality jobs. That’s why WhatCost can be your one-stop solution for all your needs!

All you need is 30 seconds to fill out our online intake form, and we’ll send you up to 3 free home-tailored quotes directly from our network of trusted installers. No costs or obligations apply. Simply click below to begin!