Avoiding cold spots with rigid thermal insulation

Eliminating cold spots: Best practice for continuous thermal performance with rigid insulation

Driven by the requirements of Part L, net zero targets and growing expectations for building performance and occupant comfort, ensuring consistent thermal performance is a design priority. While U-values are a key measure of thermal efficiency, even well-specified building envelopes can be compromised by localised areas of reduced insulation performance – commonly known as cold spots.

Cold spots in insulation are more than minor imperfections. They can reduce energy efficiency, contribute to interstitial condensation and negatively affect thermal comfort and indoor air quality. Regardless of the insulation’s specification or thermal performance rating, gaps in continuity or poorly detailed junctions can significantly reduce a building’s as-built performance. Addressing these issues supports compliance with Approved Document L, while also enhancing occupant wellbeing and thermal comfort.

What are thermal cold spots, and why do they matter?

A thermal cold spot is a localised area where heat loss is higher than specified. These weak points in the thermal envelope usually aren’t caused by the insulation material itself. Instead, cold spots are caused by interruptions in insulation continuity, such as gaps, poor detailing or thermal bridges.

David Milner, technical team lead at SOPREMA, explains how cold spots can reduce thermal efficiency, increase the risk of condensation and affect compliance: “Cold spots allow heat to transfer more rapidly through the building fabric, reducing thermal efficiency,” David says. “They can also lower the internal surface temperature, which can reduce average radiant temperature and can make spaces feel less comfortable. As a result, occupants may increase heating demand, leading to higher energy use and costs.”

How cold spots increase the risk of condensation

Condensation occurs when warm, moist air meets a colder surface. The air cools to its dew point, forming water droplets. When this happens on visible surfaces, the moisture may cause damage or stains, but it can usually be wiped away.

Cold spots raise this risk because they create areas of lower surface temperature, making it more likely that indoor air will cool to the dew point at those locations.

“More serious issues can occur when condensation forms within the interstitial areas of the building fabric, such as wall cavities or roof spaces,” warns David. “In these locations, trapped moisture may take longer to dry, and it can go unnoticed, increasing the risk of damp, mould growth or deterioration of building materials – including insulation – over time,” he explains. “Prolonged damp can also affect indoor air quality and may have a negative impact on occupant health and wellbeing,”.

How cold spots can compromise compliance

“Cold spots reduce a building’s as-built thermal performance, creating a gap – known as the performance gap – between the predicted SAP calculations and its actual efficiency. In severe cases, this may contribute to non-compliance with Part L (or the local equivalent) during as-built assessments, potentially causing project delays and added costs,” David says.

Closing the performance gap and avoiding cold spots in insulation

The performance gap – the difference between a building’s as-designed thermal performance and its as-built reality – remains a key challenge for architects, specifiers and installers.

Addressing the performance gap requires more than specifying insulation with low lambda values, David explains. “Continuous, carefully detailed insulation layers, installed in line with manufacturer guidance and supported by quality control on site, are critical to delivering the intended thermal performance and avoiding cold spots.”

BREL (Building Regulations England Part L) reports were introduced to document how a building has been constructed in relation to its design specifications. By improving visibility and accountability on site, they help reduce the risk of performance gaps and support compliance with energy efficiency standards.

It’s all in the details: common causes of cold spots in insulation

Specifying the right insulation is a critical part of ensuring thermal performance – but it’s only one part of the process. During installation, various challenges and small detailing issues can interrupt rigid insulation continuity in the building fabric, creating cold spots.

• Gaps between insulation elements – when insulation boards don't fit together tightly, small gaps can cause cold spots.
• Inaccurate cutting or placement – when insulation is cut too small or positioned incorrectly, there may be gaps at edges or corners.
• Voids around fixings – gaps created by screws, nails or other fixings can penetrate or push against the insulation.
• Poorly sealed junctions at wall–floor and wall–roof interfaces and perimeter edges – these complex areas are prone to thermal discontinuities and thermal bridging.
• Inadequate detailing around door and window reveals – gaps, poorly fitted insulation or incorrectly installed cavity trays at reveals can interrupt thermal continuity.
• Penetrations for pipes, cables and services – these create interruptions in the insulation layer.
• Incomplete insulation around structural elements – insulation may be thinned, compressed or removed to accommodate building components such as joists, lintels and steel beams.
• Inconsistent insulation between floors – particularly in refurbishment projects, insulation can be incomplete or poorly fitted at intermediate floors or ceiling interfaces.
• Poor detailing at roof junctions – roof elements, such as dormer cheeks, valleys and eaves, have complex junctions that require careful detailing to ensure insulation continuity in the building fabric.
• Discontinuity behind battens – insulation may not sit flush with the underlying substrate, creating gaps or voids.

Many of these issues can be avoided by planning the order of work carefully and ensuring technical guidance is followed on site. SOPREMA provides CAD and BIM details for common junctions to assist specifiers in integrating these details early in the design stage. “Regular quality checks during installation, particularly at complex junctions and penetrations, can also help maintain thermal continuity across the entire building envelope,” David suggests.

Installing continuous insulation: best practices for eliminating cold spots in insulation

A fabric-first approach prioritises the performance of the building’s thermal envelope rather than relying on mechanical or renewable systems to achieve efficiency.

A fabric-first approach relies on continuous insulation – a consistent, uninterrupted layer across walls, floors and roofs. Even small installation errors can cause cold spots and heat loss.

Adhering to best practice strategies throughout every stage of installation helps ensure the insulation performs as designed. To achieve a continuous insulation layer:

• Ensure board joints are tightly butted – boards should be fitted closely together to eliminate gaps that could allow air movement or localised heat loss.
• Stagger joints for multiple layers – where more than one layer of insulation is installed, joints should be offset to avoid creating weak points in the thermal envelope.
• Seal board edges as appropriate – using tapes, foams or sealants in line with manufacturers recommendations can help secure board position and prevent small gaps from compromising insulation continuity.
• Ensure substrates are clean and dry before installation – residual moisture can damage or reduce the effectiveness of some insulation materials, while dirt or debris can prevent boards from sitting flush and create air gaps.
• Position vapour control layers (VCLs) carefully – VCLs should be continuous and properly sealed at joints and penetrations to manage condensation risk and protect insulation.
• Thermal bridge prevention at junctions, corners and penetrations – careful detailing in complex areas is essential to maintain thermal continuity and minimise cold spots.

Avoiding cold spots with SOPREMA insulation

Cold spots are a common contributor to the performance gap. Even with carefully specified insulation, installation errors can reduce thermal efficiency, increase condensation risk and undermine compliance with energy efficiency standards.

Creating continuous insulation layers can help to minimise cold spots and maintain a building’s intended thermal performance. SOPREMA rigid PIR (polyisocyanurate) boards offer lambda values as low as 0.022 W/m·K, contributing to low-U values in walls, floors and roofs. Their lightweight, easy- to-cut format allows precise fitting, helping to maintain insulation continuity and prevent cold spots.

The SOPREMA range of PIR insulation products includes:

• GA4000 – is easy to install and features a low-emissivity (low-e) foil facing. It is available in thicknesses from 50–100mm and can be used for roof, floors and walls.
• TB4000 – a thermal insulation board that is easy to install, with a low-e foil facing. It's available in thicknesses from 20 to 40mm and is suitable for floor, wall and roof applications.
• PL4000 – an insulation board with a paper facing and laminated to a piece of tapered-edge plasterboard. It is available in thicknesses of 25–65mm and is suitable for roof and internal walls.

For flooring applications requiring high compressive strength, SOPREMA also offers XPS (extruded polystyrene) rigid foam insulation.

To complement our range of PIR and XPS insulation products, SOPREMA provides a variety of technical support resources. Rigid board insulation installation guides, CAD/BIM resources and detail drawings are available to support compliance and help specifiers and installers reduce the risk of cold spots. We also offer a free online U-value calculator, and our technical support team can provide project-specific guidance.

Cold spots often indicate issues with insulation continuity or junction detailing. Avoiding them requires attention to detail, early-stage planning and adherence to manufacturer guidance – as well as correct insulation specification.

By focusing on product selection and correct installation, architects, specifiers and installers can avoid cold spots, close the performance gap and maintain thermal continuity.