With over 50 years experience in the thermal insulation market, the A. Proctor Group has seen evolving energy performance and reduction in CO2 emissions driven by the government placing increasingly higher demands on the insulation performance of the building envelope. This experience has allowed us to develop a range of solutions and services to assist the construction industry in meeting these demands by considering the full range of factors influencing energy performance, from U-values and heat loss rates, to airtightness and cold bridging.
We offer a large range of thermal solutions including Thermal Laminates for roofs, walls and floors, Foam Fabrication, Tapered Roofing and Multi-foil insulation. We have also developed Spacetherm®, a thin high performance aerogel insulation, commonly used for solid wall applications. We also promote an environmentally friendly wood fibre product that is manufactured from re-cycled timber waste products.
Our technical services include U-Value calculations, Dew point predictions, SAP assessments, SBEM Calculations & Non-Domestic EPCs. We can also provide energy performance certificates for domestic properties in Scotland.
Spacetherm - Imperial War Museum, London
Here is the latest in our series about some commonly held myths in contracting concerning thermal and acoustic insulation, condensation control, fire protection, and ground gas protection. In this article, we ask the question: Is it true? The odd cold bridge is not a problem? Insulating reveals doesn’t make much difference?
Why a cold bridge, thermal bridge matters
A cold bridge, more commonly referred to as a thermal bridge, will result in additional heat loss through a conductive part of the building envelope that needs to be included in the building’s energy assessment calculation. The heat loss caused as a direct result of thermal bridging will lead to increased energy costs for buildings and homes. It is estimated that thermal bridges can account for 20-30% of the heat loss in new build houses. The drive to improve the insulation of homes will result in thermal bridging becoming even more significant. In addition, thermal bridging can lead to cold spots, adding to the risk of condensation and the potential for mould growth.
Where thermal bridges are found
Within the construction of buildings, there are typically two types of thermal bridges which can occur: • Repeating • Non-Repeating
A repeating thermal bridge will occur where poorer insulating materials intersect other layers of insulation within the building fabric. Examples include timber or steel studs in framed construction, at the point of wall ties, or the mortar joints of insulated walls and balconies. The differing heat flow due to a repeating thermal bridge can be accounted for in the “U value” calculation. Non-repeating thermal bridges typically occur at junctions where walls and floors penetrate the thermal envelope, around windows and doors, and steel lintels connecting the internal and external walls. These require more complex calculations and cannot be accounted for in the “U value” but will be accounted for by the “PSI-value” or “Y value (Ψ)”.
Thermal bridges also commonly occur due to air gaps or penetrations through the insulation layer and between the external and internal structures. So air leakage is a potential issue increasing the importance of efficient airtightness at the design stage.
Identifying thermal bridging
Part L of the Building Regulations has recently been updated, requiring a reduction of 31% fewer carbon emissions for dwellings and 27% for non-dwellings. New build homes are to be assessed under a new Standard Assessment Procedure (SAP10.2) calculation. SAP10.2 stipulates increased insulation requirements and new targets for the TER (Target Emissions Rate) calculations. SBEM will continue to be used for non-residential dwellings.
Identifying where cold bridging exists or the risk of thermal bridging can be achieved using thermal imaging. The A. Proctor Group provides comprehensive technical support, including advice on thermal bridging calculations on thermal bridging, to contractors and designers. This service helps the client to identify and specify the right material and required thickness for maximum efficiency. The calculations demonstrate the effect of thermal bridging before and after applying the chosen solution.
How to prevent thermal bridging
A popular measure of tackling thermal bridging and improving energy efficiency in buildings is installing insulation. Improving the insulation of a building is an example of a fabric-first approach to building design. In fabric first construction, the building elements are designed to reduce the reliance on external systems, such as mechanical or electrical heating or cooling systems. A fabric-first approach will maximise both airtightness and insulation.
The move to increase the insulation of buildings is not without its challenges, particularly in those areas which are difficult to insulate, e.g., existing buildings, solid wall buildings, window reveals, doorways and openings. However, the use of high-performance Spacetherm insulation can overcome this.
The Spacetherm® insulation range comprises high-performance aerogel insulation that can be bonded to various boards to suit specific applications. On its own, Spacetherm Blanket is a versatile material that is both vapour permeable and hydrophobic, making it ideal for solid wall insulation. It can be bonded to a magnesium oxide board to produce Spacetherm Multi. This can be as thin as 16mm, including 10mm of insulation and a 6mm board, making it ideal for breaking the cold bridges typically found at window reveals. Also, available in greater depths, it allows walls to be insulated to a thinner depth than would otherwise be possible. For example, 45 – 50mm of Spacetherm insulation would bring a typical wall down to the 0.3 W/ m²K required for building regulations and EnerPHit certification. In addition, Spacetherm (CBS) cold bridge strips can easily be applied to minimise cold bridges. The cold bridge strips consist of Spacetherm Aerogel insulation encapsulated in polyethelene. Spacetherm CBS is an ideal choice for timber or steel frame structures and can be cut to various widths to suit different applications.
Addressing the challenge of internal insulation, Spacetherm Wall Liner is a thin thermal laminate of about the thickness of a standard layer of plasterboard. It consists of 10mm of Spacetherm insulation and a 3mm Magnesium Oxide board adhered to the wall to provide significant thermal retention compared to the uninsulated wall. Typically, it would bring a solid stone wall (with a starting u-value of around 2.3 W/m²K) down to a U-value of between 0.7 and 0.9, representing a noticeable drop in energy lost through the wall.
Another area where we encounter the challenge of cold bridging is façade retention projects. Often in these projects, most of the building is demolished and replaced with a modern new-build structure, retaining only the facade of the existing structure. Air leakage and cold bridging are the most significant problems to be overcome, so by combining a vapour-permeable, self-adhering air barrier membrane with a layer of high-performance insulation, Wraptherm offers an ideal solution to address these.
Wraptherm® is installed on the reverse of the retained facade stonework. However, as Wraptherm is vapour-permeable, it does not adversely affect moisture movement through the facade stonework. This helps limit the damage that can occur when moisture flow through older stonework is altered by refurbishment works.
As well as protecting the existing building fabric, Wraptherm’s hydrophobic properties provide a secondary barrier to water ingress, sealing tightly to door and window frames and other penetrations and limiting heat loss associated with air leakage. The unique layer of aerogel insulation in the Wraptherm also effectively limits cold bridging by providing a continuous insulation layer across the back of the facade. Hence, there is a thermal break between the new structure internally and the cold outer stonework, further boosting the energy performance of the upgraded building. Combining these properties into a single material, Wraptherm speeds up and simplifies the installation process and reduces on-site defects and requirements for costly remediation.
It is crucial that contractors understand the importance of preventing and reducing the occurrence of cold bridges in building construction. Even the odd cold bridge will reduce the energy efficiency of the building, leading to higher energy costs for the users and, at the worst, failure to comply with the requirements of the latest building regulations. We have placed significant investment in developing some of the most effective high-performance solutions to address the challenge of hard-to-insulate areas such as window and door reveals, ensuring a fabric-first design approach and reducing the gap between “as-designed” and “as-built”.