What Are Accredited Construction Details?

Accredited construction details (ACDs) are standardised details developed in 2002 to ensure minimum energy efficiency performance standards are met in construction projects.

Design and construction teams work with ACDs to identify focus points, such as insulation continuity, to minimise thermal bridges and heat loss. This data gives insight into what accredited construction junctions you need to follow.

Continue reading to learn more about accredited construction details and their role in the construction industry. 

Types of Construction Details

Construction details are used mainly by architects and builders, and the type of construction determines the grouping of the junctions. Some common junction details include:

  • Steel Frame Construction Details include details for light steel frame construction. The requirement is that insulation be placed on the outside of the steel frame to create thermal breaks and avoid condensation. 
  • Masonry Cavity Wall Details cover brick outer leaf construction but also apply to other substitute masonry materials that don’t reduce thermal performance or increase technical risks. These materials include blockwork with render, tile hanging, and weatherboarding.
  • Timber Frame Construction Details account for wall thicknesses ranging in stud size from 89mm to 150mm. Timber construction details suggest various structural forms that can influence the thermal performance of walls.
  • External Wall Construction Details cover the construction of insulated external elements of solid masonry walls. For external walls, you must consider different wall cladding materials that won’t reduce thermal performance when swapped.
  • Masonry Internal Wall Insulation Details refer to internally insulated cavity walls. This type of construction calls for your insulation board to be 75mm thick. 

The History of Accredited Construction Details

ACDs describe how to construct standard details, focusing on insulation continuity and air tightness. Designers, building control bodies, and contractors had a checklist to ensure thermal bridging prevention. 

These junction details help design buildings that meet performance standards and demonstrate energy efficiency as set out in Part L of the Building Regulations.

For example, if you wanted to construct a bay window, you’d have bay window construction details drawn up based on the ACDs. This window construction detail would then closely need to match the ACD to ensure proficient thermal performance. 

However, considering that ACDs don’t provide a wholesome look at the energy performance of buildings. PSI value (ψ-value) calculations have become a more dependable way to accurately measure thermal performance — giving building designers a comprehensive picture of the projected thermal performance.

Why Have Accredited Construction Details Become Obsolete?

Since the introduction of Part L building regulations in 2021, these details are no longer sufficient to determine energy performance. 

Heat loss can’t be accurately measured by just U-values since it doesn’t account for other junction details. U-values assess the rate of heat escape through the thickness of building components. ACDs then state the specific U-values your design should meet to be compliant. 

Therefore, a more comprehensive way is needed to measure the higher thermal performance standards — enter PSI value calculations

Part L Building Regulations 2021

These regulations were introduced in 2022 to help fast-track the achievement of the 2025 energy performance standards in the UK. The aim is to reduce carbon emissions by 31% for dwellings and 27% for other buildings. 

The goal is to deliver building stock that can achieve the overall efficiency standards to deliver net zero carbon without retrofitting by 2050.

To get there, designers need to significantly reduce carbon emission levels and ensure that there’s a decrease in the use of fuel and power in new build constructions. 

PSI Value Calculations

PSI values give designers a more comprehensive insight into thermal modelling SAP adherence. They provide an overall look at the thermal element performance by calculating linear thermal transmittance (br497).

PSI calculations offer detailed insight into the actual building performance by accounting for different temperature factors, thermal bridging, and air leakage. 

Using thermal modelling software provides precise and accurate data and promptly helps calculate your project’s ψ values. 

Importance of Accurate Thermal Bridging Calculations 

Thermal bridges occur where two exposed thermal elements meet. These thermal bridges cause cold spots in buildings due to increased heat loss and the opportunity for condensation. This renders the insulation levels ineffective and increases the energy consumption of standard builds.

Without considering thermal modelling, your heat loss calculations will be inaccurate.

With PSI calculators like AutoPSI, building designers can enter the relevant Y value numbers, customise their junction details, and quickly receive precise thermal modelling insight. 

These calculations consider more than just accredited details for insulation and showcase the following benefits. 

Bridging the Performance Gap

Building performance gaps occur when the projected energy consumption of the building doesn’t match the actual consumption levels after the build is completed. This could be a result of inaccurate thermal calculations. 

With precise data, attention to detail, and collaboration before and during construction, buildings can perform as designed. In turn, this helps prevent high energy bills and emission levels. 

Improved Occupant Health

Thermal bridges affect energy consumption and also occupant health. 

Thermal bridges often create cold spots, which allow condensation to form due to the difference in surface temperatures. The water droplets from condensation can cause mould to grow, causing a health hazard. 

Accurate heat loss calculations can help prevent thermal bridges and reduce the health risks associated with mould formation.  

SAP Compliance 

Precise numbers help demonstrate adherence to relevant building specifications. Simply completing a checklist for ACDs doesn’t provide as accurate a representation of the heat loss risks. 

With PSI calculations, you’re providing more than just assumed values in your calculations. This results in a compliant building throughout the design and construction phases — reducing the occurrence of discrepancies. 

Meeting Energy Efficiency

Accurate data can lead to a good energy proficiency certificate (EPC) rating. The thermal modelling EPC looks at how your building measures up against its predicted energy performance. 

If your design calculations match the building output, you can easily score an A on your EPC. Showcasing that the building is positively contributing to reduced emissions and energy consumption. 

Our PSI value calculator is BRE-accredited and meets ISO requirements. Try AutoPSI today and easily ensure building performance compliance.

AutoPSI: Innovative Thermal Modelling Software

With more emphasis being placed on PSI values, it’s crucial for design teams to keep up with technological advancements to ensure better compliance with construction standards in the UK.

At AutoPSI, we provide a speedy online-only tool to help you quickly calculate accredited PSI values. Our solution is best used in the design stage to monitor projected heat flow and adjust designs accordingly.

Our thermal calculation software helps streamline processes. With one tool, you can request junction details from builders, calculate PSI values, and submit documents to build. Stay fully compliant with relevant regulations by relying on innovative tools like AutoPSI. 

Want a sure-fire way to complete ψ value calculations? Sign up for a demo and discover how AutoPSI can help you with your commercial and residential builds.