Transparency, testing and thermal performance builds trust in the supply chain

Taking time to reflect on U-values

Offsite manufactured structural timber buildings are designed to deliver quality construction with high insulation values and good airtightness using a truly sustainable material. Using reflective wall membranes both on the cold and warm side of the insulation can enhance the level of thermal performance and improve the energy efficiency of the structure. The thermal resistance (R-value) is the key metric to gauge the thermal performance of reflective membranes, however the measured values can vary based on how the material has been tested, for example, testing pre and post ageing, the distance of fixing centres used and whether logos have been printed on the surface of the membrane. What may seem like small changes to R-values in numerical terms can alter the final U-value of the wall structure, so it is important to understand which factors have been considered by the membrane manufacturer as part of the calculation. If reflective wall membranes from competing suppliers are being compared for thermal performance and being plugged into a wall U-value calculation for example, it is critical that like-for-like technical data can be assessed and decisions taken based on the same parameters on a worst-case scenario. When the correct aged value is used that incorporates printed logos and the correct fixing centres, this gives transparency to the U-value achieved for the overall wall build-up.

The current STA Advice Note 18 guidance published by the Structural Timber Association for external wall breather membranes has brought transparency into sharp focus by highlighting the need for all manufacturers to clarify and verify technical data provided. This includes data for reflective wall membranes which must be tested to the required thermal and emissivity performance standards, claiming aged surface emissivity (Ɛ) and thermal resistance R-value figures (m²K/W) which are fully independently verified by a third-party, UKAS accredited certification body.

At Glidevale Protect, we provide full transparency on the testing of our products via independent third-party certification, so we’re able to fully support our customers by providing aged thermal resistance values on our reflective membranes to accurately reflect real life performance figures in a worst-case scenario. For example, our own best practice ensures that all thermal resistance results consider any logo printing on the low-emissivity surface with no greater than a print area coverage of 2% and are based on the external wall membranes being installed with the appropriate maximum horizontal fixing stud centres of 600mm as recommended in STA Advice Note 18.

Our approach to product testing

As a UK producer for over 40 years with two manufacturing facilities, we’ve been continually investing in the development and testing of our reflective membrane product range, ensuring that we provide reliable technical information that is fully supported and audited yearly by a UKAS accredited third-party certification body. This not only ensures that all performance claims can be checked and verified but also provides specifiers and architects with a clearer view of how our products can help achieve compliance, particularly important as the golden thread of building information becomes a reality.

Why clarity of product claims is important

Helping specifiers identify how best to achieve compliance with all relevant regulations, standards and guidance, by providing substantiated technical information is also vital to bridging the ‘performance gap’ so that buildings are as energy efficient in operation as they were designed to be. To navigate this potential risk, at Glidevale Protect we ensure that all our product information is regularly updated when required and is easily accessible via our website, with all specifications designed to be written to be both comprehensive and clear.

Putting ‘hidden protectors’ into focus

When building homes of the future, a key consideration should be how to create homes that are airtight and thermally efficient to prevent heat loss, whilst ensuring that the property can still ‘breathe’ and provide indoor air comfort for occupants. The correct balance between thermal efficiency, airtightness, ventilation and condensation control is a challenge that we believe can be successfully overcome through early engagement and close collaboration with a supply chain partner that can deliver a holistic solution and compliance across all these areas. To support this, we’ve invested in our own in-house resources, ensuring the continuous development of our product range to comply with the relevant regulations and standards to ensure compliance for both the UK and Irish construction markets. Our business is accredited to the ISO 9001 quality standard, along with environmental and energy management standards ISO 14001 and ISO 50001 as well as the international health & safety standard ISO 45001. In addition, we have also achieved STA Assure Gold Level status to ensure complete customer assurance, and at a product level, Glidevale Protect’s reflective wall membranes are independently certified by BM TRADA and have third-party verified Environmental Product Declarations (EPDs) to provide clear sustainability and life cycle assessment data.

Offsite manufactured timber framed buildings are designed to deliver the level of thermal performance required to make new homes as energy efficient as possible, and this is enhanced by the installation of reflective wall membranes, otherwise known as ‘hidden protectors’, within an open or closed timber frame panel system. Used within a still airspace, the high-quality aluminium foil that faces into the void helps create a ‘low e cavity’ which provides an additional insulating benefit within the fabric of the building, helping to retain heat within the structure.

Glidevale Protect offers one of the broadest collections of floor, wall and ceiling membranes available from a single supplier. We are also committed to ensuring that we can offer our customers technical transparency that ensures the accuracy, and clarity, of all product information.

Our product solutions

Glidevale Protect has developed an effective wall membrane system, comprising three of our reflective, low emissivity and insulating construction membranes for use within a closed frame timber frame wall panel construction. The system includes Protect TF200 Thermo or Protect Thermo Extreme (the latter for very severe, exposed locations) installed as the external wall breather membrane on the cold side of the insulation, with Protect TF InterFoil within the timber frame stud on the back of the OSB and our air and vapour control layer Protect VC Foil Ultra installed within a service void on the warm side of the insulation. By combining reflective membranes as part of a system within a timber frame panel and facing these into still airspaces, potential insulation savings can be generated, whilst helping to maintain a low U-value for the building element. This can help achieve the more onerous targets in Building Regulations Part L as we move towards the Future Homes Standard, reducing the need to increase the wall’s overall footprint.

Taking a fabric first approach using a reflective membrane system relies on the early and considered specification of products. Membranes not only protect new homes from the elements as a primary line of defence during the build but also act as the secondary line of protection against water penetration after the construction and during the life of the building. This helps to create a safe, healthy and thermally efficient interior that is free from interstitial condensation and is cost-effective to heat.

Improving thermal performance as a radiant barrier

Installing Glidevale Protect’s combination of reflective membranes into a timber frame structure provides a boost to the overall thermal performance of a wall structure, without increasing the footprint of the building. By facing the reflective membrane surface into still airspace cavities within the structure, for example a service void between the internal plasterboard and frame as well as the cavity between the sheathing board and external cladding, the introduction of low-emissivity, reflective surfaces within these cavities can improve the thermal resistance of the associated air space. If the specified membrane offers low-emissivity performance within a still airspace, this means its thermal resistance to heat flow is increased, thereby achieving a high R-value when used within the cavity. For example, using the reflective Protect TF200 Thermo or Thermo Extreme membrane in the external wall cavity can improve the thermal resistance (R-value) from 0.180 m²K/W to an enhanced 0.77m²K/W. This thermal resistance (R-value) is an aged result, so is worst-case scenario, incorporating print onto the foil surface and installed at the correct fixing centres. Comparing like for like using aged results, an R-value of 0.77m²K/W (0.03 emissivity) for Glidevale Protect reflective membranes is better performing than a competitor product with an R-value of 0.66m²K/W (0.05 emissivity) and can result in lower overall U-value calculations being obtained for the wall build-up.

The low-emissivity surface of reflective membranes such as Protect TF200 Thermo and Protect VC Foil Ultra is achieved by the material composition – a high purity, solid aluminium foil is used which acts as a barrier to infrared radiation. Emissivity is a measure of a material’s ability to emit thermal radiation (so the flow of heat loss within a wall structure) and is defined as a unitless ratio between 0 and 1, with 0 being a perfect barrier and 1 a perfect blackbody or emitter. Reflectivity is the inverse of emissivity and defines the material’s ability to reflect incident radiation back into a structure with 0 being perfect absorber and 1 a perfect reflector. Taking Protect TF200 Thermo as an example, the independently certified and measured emissivity for this material is 0.03, which equates to reflectivity of 0.97, or in percentage terms, the membrane has a high 97% reflectivity. This makes Glidevale Protect’s reflective membranes ideal for use on both the warm and cold side of the structure to minimise heat loss through the element, acting as an insulating material that adds value to a wall build-up. Additionally, external wall membranes such as Protect TF200 Thermo will help to minimise heat gain during warmer, summer months by providing a barrier to radiated heat from the external cladding. When specifying reflective membranes, a simple way to remember the link between thermal resistance and emissivity is that the lower the ‘E’ (emissivity), the higher the ‘R’ (thermal resistance) and the better the membrane’s thermal performance when facing into a still airspace.

In summary, membrane products providing the important benefit of thermal efficiency and the management of radiated heat, need to be aligned with technical transparency in order to develop trust with specifiers, end clients and developers. With some reflective membrane suppliers quoting R-values ranging between 0.78 m²K/W and 0.81 m²K/W with no clarity on whether thermal resistance testing has involved correct installation and in the aged condition, important questions need to be asked. Any supplier worth their salt should be able to provide clear, unbiased information about their products when asked the key questions during a product benchmarking exercise – is the thermal resistance data aged and quoted in the worst-case scenario? Does testing incorporate printed logos which can affect the overall emissivity of the surface? Does the thermal resistance value achieved use realistic and correct fixing centres that would be typically used on a timber frame wall panel and is the claimed result in line with testing requirements? If these questions can be answered effectively, are backed up by independent, third-party certification and meet the guidance requirements detailed in STA Advice Note 18 then the due diligence offered by the membrane supplier can help set it apart as a market leader, showing integrity and gaining credibility with construction specifiers and timber frame manufacturers. Ultimately, correct and transparent thermal resistance values are critical in order to not over inflate the overall performance level of the wall structure, ensuring reassurance in specification and helping to bridge the design gap.

To find out more, call 0161 905 5700, email info@glidevaleprotect.com or follow Glidevale Protect on LinkedIn.