Offsite manufactured structural timber frame buildings are increasingly being designed to deliver added pre-manufactured value (PMV) thanks to the construction of highly insulated and airtight panels in order to maximise energy efficiency. In this blog, we look at how reflective wall membranes are integral insulators within the building envelope to help improve the energy efficiency of a building.
//Back to Basics: What Do We Mean by ‘Reflective Membranes’?
Reflective wall membranes, sometimes referred to as ‘hidden protectors’ are installed within an open or closed timber frame panel system, enhancing the thermal performance of a building. 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, blocking radiant heat transfer.
//Why Build with a Reflective Membrane Layer?
By combining reflective membranes as part of a system within a timber frame panel on external and internal walls 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, as well as reduce the need to increase the wall’s overall footprint. Used within the cavity, the reflective membrane operates as a radiant barrier with a thermal resistance to heat flow. This low emission of infra-red radiation means that the heat is reflected back into the property to ensure long term performance. In the warmer, summer months, the membrane minimises heat gain by providing a barrier to radiated heat from the external cladding.
The thermal performance of reflective wall membranes is an added enhancement for the construction. This is in addition to the main requirement for the membrane to protect new homes from the elements as a primary line of defence during the build as well as acting as the secondary line of protection against water penetration during the life of the building when it has been constructed. In addition, with a breather membrane also ensuring vapour permeability, this helps to create an overall safe, healthy and thermally efficient interior that is free from interstitial condensation and is cost-effective to heat.
//How Do Reflective Membranes Work within a Timber Frame Structure?
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.
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 low-emissivity, reflective surface 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. This will in turn achieve a high R-value (m2K/W) when used within the cavity.
It’s important to ascertain whether the R-value claimed for a reflective membrane is the aged result and is tested in the worst case scenario. Logos printed on the low-emissivity surface of the membrane also must be taken into account as part of the testing process, along with the maximum horizontal fixing stud centres of 600mm as recommended in Structural Timber Association’s (STA) Advice Note 18.
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.
//Understanding the True Value of Reflective Membranes
Glidevale Protect is a specialist in energy efficiency, ventilation solutions and condensation control, offering a range of building products including construction and airtightness membranes, roofing underlays, roof ventilation, and cavity trays.
The construction membrane range includes reflective, insulating external wall breather membranes including Protect TF200 and Protect Thermo Extreme which enhance the overall thermal efficiency of many wall types and are ideal for offsite construction projects. And for internal walls, our Protect VC Foil Ultra is a robust, highly reflective air and vapour control layer (AVCL), offering low emissivity to enhance the thermal performance of walls, ceilings and floors. Glidevale Protect’s external and internal wall membranes can be used together as part of a system, to not only achieve lower overall U-values but to help reduce the thickness of the required insulation.
Achieving the correct balance between energy efficiency, airtightness, ventilation and condensation control is a challenge that can be successfully overcome through early engagement and close collaboration with a supply chain partner like Glidevale Protect to deliver a holistic solution and compliance across all these areas. As a UK producer, we are committed to providing full technical transparency on all our products so specifiers, end clients and developers can trust our results are accurate and reliable for real world environments.
To find out more, visit www.glidevaleprotect.com, call 0161 905 5700, or email info@glidevaleprotect.com or follow Glidevale Protect on LinkedIn.
