The Fabric-first Solutions You Need to Consider for Part L Compliance

There’s more to meeting the latest requirements of Part L than meets the eye and, as John Mellor from leading UK building materials manufacturer Glidevale Protect explains, ‘hidden protectors’, such as reflective breather membranes and vapour control layers, can make a difference to the thermal efficiency of a building.


Set against a roadmap of Building Regulation changes, specifiers need tried-and-tested products that can offer a holistic solution that is more than the sum of their parts. Improving the energy efficiency and thermal performance of a dwelling is essential to achieving compliance with the more onerous requirements of Part L, which is now mandatory for all new buildings, but already, the industry is looking to futureproof ahead to meet the next wave of targets that will come in with the Future Homes Standard in 2025. As the way we design and construct buildings is evolving to meet more stringent targets, manufacturers have an important role in developing suitable products that are technically fit for purpose and help improve thermal efficiency of the building envelope, delivering low U-values, which can be achieved in practice.

The Part L balancing act

From energy-saving windows and doors to the greater use of insulation, there are many building materials that can contribute to improving the overall thermal efficiency of a building and considering all the elements that make up the building fabric is essential. How can this thermal performance be managed alongside a condensation control strategy or the need to ventilate correctly? What if there was a solution that could save money as well as energy by limiting the need to increase the amount of insulation required and the footprint of the wall while still contributing to and enhancing the thermal performance of a building?

This is where system solutions that are installed within the wall structure, such as reflective breather membranes and air and vapour control layers, can make a huge difference, and although they are out of sight as ‘hidden protectors’, they certainly shouldn’t be out of mind.

Reflective wall membranes for improved thermal efficiency

The correct specification and accurate installation of wall construction membranes are vital. The most energy-efficient membranes are those with low emissivity reflective surfaces, which provide an additional insulating benefit for the wall structure. As the effectiveness of a reflective membrane is dependent on the quality and purity of the foil-faced surface in terms of how it performs as a radiant barrier, choosing products that feature high-quality aluminium and provide good aged thermal resistance is recommended. When used within the wall using a still airspace, such as a service void, for example, aluminium reflective membranes can significantly reduce radiant heat transfer and heat loss, ensuring the cavity becomes low emissivity, which is a key part of helping improve energy efficiency in buildings.

AVCLs to prevent air leakage and heat loss

Airtightness can be boosted by using specialist air and vapour control layer membranes (AVCLs), which are installed on the warm side of the insulation to further limit heat loss. When installing an AVCL, it’s essential to create a continuous airtight seal, paying particular attention to service penetrations, overlaps and junctions between different elements, such as a wall and floor or a window and wall. Any gaps, however small, can become thermal bridges where heat can easily escape and cause an accumulation of condensation, which, in turn, can cause mould and mildew to form. To create a reliable and continuous seal, the use of specialist adhesive tapes, which have a high tack adhesive, offers greater accuracy than traditional double-sided tapes or mastic sealant.

Control layers to control condensation

Creating a well-sealed and thermally-efficient home is only part of the challenge. Without a considered plan to balance airtightness with ventilation and reduce the risk of condensation, problems will arise that can negatively impact both the health of the building fabric and the residents within. Again, the development and specification of air and vapour control layers can provide an effective solution as well as combining this with a suitable building ventilation solution. A ‘build tight, ventilate right’ approach can help ensure a healthy and energy-efficient home is specified.

For structural timber-framed homes built using offsite construction methods, it’s important to also consider the installation of an external wall breather membrane to the cold side of the insulation. Not only can this help prevent water from penetrating and damaging the exterior of the building during construction, but breather membranes can significantly reduce the risk of interstitial condensation and the formation of damp patches. When used as a system of wall membranes within a timber-frame closed panel, for example, the combination of an AVCL and breather membrane can provide benefits in terms of condensation control, and if low emissivity reflective membranes are used, this can ensure greater thermal performance and a lower overall U-value.

Help is at hand

Early engagement with product manufacturers at the design stage is the best way to gain a deeper understanding of how specialist construction membranes can bring tangible benefits to a project. As regulations change and environmental targets tighten, it’s important to futureproof the specification process by identifying products that can maximise the efficiency of a build in more ways than one and uncovering the benefits of these ‘hidden protectors’ is a good place to start.

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