Fabric first paves the way to net zero

[edit] The importance of a fabric first approach and how choosing the correct lintel specification can have a positive impact on the SAP calculation.

Faced with stricter Building Regulations and the UK’s ambitious commitment to bring carbon emissions to net zero by 2050, designers are under increasing pressure to consider the long term energy efficiency of all buildings from the earliest stage of the design process. All new housing in 2025 is expected to produce 75-80% less carbon emissions compared to current standards under the Future Homes Standard and will therefore require low carbon heating technologies.

However, it is clear that a fabric first approach within SAP will be crucial to comply with new Part L regulations and is a critical first step to reaching the performance levels required and future-proofing UK homes. It is why the specification of thermally efficient lintels is one of the most cost effective ways to address thermal bridging at non-repeating junctions and keep us on the critical path to net zero.

The Government is committed to bringing in the Future Homes Standard (FHS) in 2025, which will see a new build house have 75% lower CO2 emissions than one built to today’s standards. This will be achieved by having very high standards of energy efficiency and low carbon heating (i.e. heat pump). Part L 2020 will be an important stepping stone to the FHS, but to put things into context the previous Part L uplift in 2013 was 6%. Therefore, the 31% uplift this time around will require some fairly significant changes for housebuilders, as ultimately we need our homes to be zero carbon ready to meet future legislation.

[edit] Fabric first approach to design

What will this mean for new homes and how will designers meet these rigorous standards? One key area will be addressing the thermal performance of a building envelope through a fabric first approach to building design. If we get the fabric right and we build as designed, we will go a long way to meeting our targets. It is an approach that will enable us to meet and even exceed regulatory performance criteria, whether it is for large scale social housing or a much smaller residential property.

Whilst a reduction in CO2 emissions is one consideration when designing thermally-efficient housing, an improvement in thermal comfort can also have a positive impact on occupants – adding to their thermal comfort, productivity and wellbeing.

[edit] Eliminate thermal bridging

A critical element of the fabric first approach will be addressing the issue of thermal bridging, which can be responsible for up to 30% of a home’s heat loss. Eliminating thermal bridging through good design and correct product specification will be essential if we are to ensure we meet these ambitious new regulations.

Whilst there are some design, measurement and calculation issues, the other concern in terms of thermal bridging is that we are neither building consistently
what we design, nor detailing the right products in the right places. There are also issues with site skills and workmanship; when you fail to build correctly it undermines the good work carried out in the first instance. This can lead to a performance gap between as-designed and as-built building performance. It is why these weak spots can significantly impact a building’s heat loss and have a detrimental affect on the overall fabric efficiency of the external wall.

[edit] Thermally efficient lintel

Often overlooked when it comes to thermal efficiency due to a focus on insulation, window and doors, is that traditional steel lintels can create a significant thermal bridge in homes. This is due to the high thermal conductivity of steel and because they span over long lengths in a typical build. However, there are solutions to address this.

For instance, Hi-therm+ has set a new standard for thermal efficiency in steel lintels. It incorporates a thermal break and is up to five times more thermally efficient
than a standard lintel. Hi-therm+ is a very cost-effective solution, particularly if we look beyond the unit price, as getting the fabric right will save energy throughout the entire life span of the house.

The Hi-therm+ lintel has made a significant impact on the thermal efficiency of homes and is specified on many housebuilder projects around the UK due to its low cost and improved performance in lowering carbon emissions within the Standard Assessment Procedure (SAP).

The importance of lintels should not be understated. The Hi-therm+ lintel has a positive impact on the SAP calculation due to its impressively low thermal conductivity performance, which contributes towards its Psi value of between 0.03 & 0.06 W/m.K. This makes it the ideal low cost and sustainable solution for specifiers aiming to achieve building regulations with the fabric first approach. When you consider the BRE has found that thermal bridging can account for up to 30% of heat loss from buildings, then paying close attention to the details and structural elements such as lintels can have a huge impact on the overall thermal performance of a building.

At a time of spiralling energy costs and the current energy crisis showing no signs of abating, making homes more energy efficient through a fabric first approach will go some way to locking in savings for the lifetime of a building and achieving our climate change target.

So with changes on the horizon for the design of our new build houses, it will be incredibly important for architects to specify materials and components which deliver where others cannot – as this can be the difference between a sustainable and an inefficient home.

Article written by Chris Cowley, National Specification Manager, Keystine Lintels originally appears in the AT Journal summer issue number 142.

--CIAT

[edit] Related articles on Designing Buildings

• Accredited construction details ACDs.
• Assessing the effects of thermal bridging at junctions and around openings.
• Building fabric.
• Conventions for calculating linear thermal transmittance and temperature factors.
• Interstitial condensation.
• Reducing thermal bridging at junctions when designing and installing solid wall insulation FB 61.
• Solid wall insulation.
• Thermal imaging to improve energy efficiency in building design.
• Thermographic survey.
• Thermal bridging in buildings.
• Thermal indices for the built environment.
• U-values.