Understanding Building Regulations relating to Insulation

Whether you are involved in a new build or a refurbishment project, there are a certain set of standards for thermal insulation which need to be adhered to according to Building Regulations. These standards are set out by the government and approved by parliament. In order that we can design energy-efficient homes, and that we meet compliance, it is vital we understand these building regulations.

In order to provide an understanding, let us first look at the individual sections which need to be considered.

In England, Approved Document L: Conservation of Fuel and Power sets out the standards for the energy performance of new and existing buildings. When it comes to insulation, Wales has its own separate set of standards which are described in Document L1A & B (Wales) and Scotland has specific standards set out in Section 6 (Energy) of the Scottish standards.

There are four parts to Approved Document L:

• Approved Document L1A: New dwellings (Domestic)
• Approved Document L1B: Existing dwellings (Domestic)
• Approved Document L2A: New buildings other than dwellings (Non Domestic)
• Approved Document L2B: Existing buildings other than dwellings (Non Domestic)

There are two parts to Section 6

• Building Standards Technical Handbook (Domestic)
• Building Standards Technical Handbook (Non Domestic)

Each standard sets the levels of thermal insulation required for your build. This value is expressed as a U-value. In order to understand how we meet compliance let us now look at what a U-value is.

What is a U-value?

A U-value is a measure of heat loss in a building element such as a roof, wall or floor. It can also be referred to as an ‘overall heat transfer co-efficient’ and measures how well parts of a building transfer heat. This means that the higher the U-value the worse the thermal performance of the building envelope. A low U-value usually indicates high levels of insulation. They are useful as a way of predicting the composite behaviour of an entire building element rather than relying on the properties of individual materials. U-values are measured in W/m²K.

U-values are important because they form the basis of any energy or carbon reduction initiative. In practice, nearly every external building element has to comply with thermal standards that are expressed as a maximum U-value. Knowledge of how to simply calculate U-values at an early stage in the design process, avoids expensive re-working later in a project. It allows the designer to test the feasibility of their project at an early stage to ensure it is fit for purpose and will comply with regulatory frameworks.

Now we know what a u-value is, let’s look at how each individual part of Document L influences the amount of insulation required to meet building regulations.

New Build, Domestic (L1A England)

Building Regulations Part L set out clear guidelines on how to make a new property more energy efficient. This is measured with TER (Target Emissions Rate) and is based on elements such as insulation, heating, lighting, building materials and windows. This value is calculated via a system known as Standard Assessment Procedure or SAP which calculates the CO2 emissions and in the case of England, the energy demand of the proposed specification. This procedure includes stating specific U-values of each element used in the house.

The below drawing shows the U-value requirements set out for new properties in the Building Regulations for each element (roofs, walls and floors). The actual specification required for a compliant building and necessary building fabric U-value target may vary depending on the actual overall proposed specification and the outcome of the energy assessment.

Existing Dwellings, Domestic (L1B England)

Existing dwellings differ from new dwellings, in that they do not have to achieve a whole building Target CO2 Emissions Rate (TER, see New Dwellings above). However, existing dwellings do have to meet certain target U-values for building elements (roofs, walls and floors); each of which are shown in the below drawing.

New & Existing Buildings, Domestic (Wales)

Wales has its own set of standards when it comes to insulation which states differing U-Values to the standards that apply in England. The drawings below show the U-value requirements for both new and existing domestic buildings.

New Dwellings

Existing Dwellings

New & Existing Buildings, Domestic (Section 6 Scotland)

The relevant building regulation relating to insulation in Scotland is Section 6 (Energy) of the Scottish standards which states that every building must be designed and constructed in such a way that an insulation envelope is provided which reduces heat loss. The drawing below shows the maximum U-values for each building element.

New Dwellings

Existing Dwellings

The information shown in the U-value drawings shown is provided for guidance only. You should consult your building control authority and building designer regarding compliance with building regulations. Now we know what a U-Value is and what target U-Value we need to achieve, let’s look at what information is needed to calculate a U-Value.

Calculating U-Values

To calculate the U value of a building element such as a roof, wall or floor, we need to know the build-up of that element. Each building material should be positioned properly in sequence. The properties of each element / building material are required to enable us to calculate the overall u-value as accurately as possible.

Use our handy online U-value calculator today to determine the optimal U-Value for your application.

Require a bespoke U-Value or Condensation calculation for your project?

Contact our technical team on 01909 726025 or technical@ybsinsulation.com

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