Thermal bridging

Sustainability in building design is a hot topic, with developers doing all they can to build more energy efficient buildings. Simon Fielden, sales director at SFS UK, discusses what specifiers should consider in order to make building envelopes as thermally efficient as possible

Under the Climate Change Act, the UK Government has set a legally binding target to reduce national greenhouse gas emissions by at least 80% by 2050. The challenge architects and specifiers face today is to ensure all buildings meet the energy efficiency levels and sustainability required, whilst providing comfort, aesthetics and safety.

According to Designing Buildings, badly insulated houses experience 35% of heat loss through their walls, and around 75% of an industrial unit’s heat is lost through the building fabric (Carbon Trust).

The often-used idiom ‘The devil lies in the detail’ is apt here as although the desired thermal performance (U-value of a façade) may seem relatively easy to achieve, the requirement of numerous rainscreen subframe components such as brackets into a design can adversely affect the insulation performance hugely.

Rating the thermal value

Thermal transmittance is commonly known as the U-value, which is the rate of heat transfer through a structure, measuring heat loss and thermal performance. U-value is the measurement in which a building is deemed energy efficient.

Often, the choice is to increase the external layer insulation to combat this issue and help retain heat in the building. However, this solution isn’t quite so simple, as it means that brackets need to be larger to accommodate the thicker layer of insulation which impacts on the structural integrity of the envelope as well as costs.

The most effective way to reduce heat loss is through the robust design and construction of a well-thought-out building envelope, with careful attention to the selection of rainscreen subframes chosen to produce the appropriate and optimum level of thermal performance.

By doing so, the thermal performance of both commercial and domestic properties can be increased considerably, without the need for additional or thicker insulation. Which in turn may add to the cost further and won’t be possible due to space or footprint restraints of the building.

Thermal bridging – a leading cause of heat loss

When subframe assemblies are under specified it can lead to excessive thermal cold bridging.  Thermal bridging happens when there is a thermally conductive connection i.e. a rainscreen subframe bracket, between the inside and outside of a building which penetrates the insulation layer. The additional heat loss caused by a thermal bridge is called the ‘point thermal transmittance’ or ‘Chi’ value which is measured in (W/(m²K)).

This ‘bridge’ results in wasted heat transfer across the connection, changing the internal surface temperature. Thermal bridging can also cause condensation, as warm, damp internal air is meeting the cold surface, causing further issues such as mould growth.

Recent research by the BRE (Building Research Establishment) has shown that thermal bridging may be responsible for up to 30% of a dwelling’s heat loss. As legislation becomes more stringent and energy awareness more acute, the drive to ever more thermally efficient facades becomes increasingly important.

To minimise this thermal bridging effect and to not have to use oversized brackets and thick layers of insulation, specifiers can either look to use alternative bracket materials or use insulated thermal pads attached between the bracket and the fixing structure.

In doing so, they will be reducing thermal bridging, improving their U-value rating and prolonging the lifespan of the building. By doing this, contractors can also inherently comply with Part L 1A and 1B of the Building Regulations, legislation that focuses on the conservation of fuel and power in both new and existing dwellings.

Optimised thermal solutions & superior performance

The ideal thermal design for a project can be achieved by the selection of the most appropriate rainscreen support or subframe system, optimised for performance and budget.

3D thermal modelling is used to calculate thermal point loss in the data, from which it is utilised to dynamically calculate the required insulation thickness needed to achieve the desired U-value for a design. Such calculations must conform to EN 10211:2007.

Requirements for each rainscreen cladding project are often different and depend on various factors such as wind load, building height and substrates used. SFS’ Project Builder calculation tool is designed to submit project specific data and provide an NVELOPE® subframe solution which includes indicative m² rates and preliminary static calculations.

There are a number of methods and materials that can be used to counter thermal bridging effects caused by brackets. These include thermal insulation pads, brackets made from higher thermally resistant materials, or a combination of both.

At the heart of SFS’ NVELOPE® Thermal Solutions is a high performing thermal pad which insulates the bracket from the primary wall structure, created to minimise thermal point loss. The unique design guards against thermal degradation caused through the compression when fixed to the façade, ensuring no loss in thermal performance.

The race to improve buildings’ thermal performance

For global warming and climate change to slow down and even reverse, the way buildings are constructed must change too.

As architects and specifiers strive to meet stringent building regulations and improve energy efficiency, they must work together to ensure a successful construction in the details of the building envelope. SFS is committed to this cause and helping you find the perfect rainscreen and building envelope solution that meets your needs and secures the future of our built environment and our world.

In our upcoming whitepaper, entitled ‘The effects of rainscreen subframe systems on the overall performance of external walls’, we have analysed the performance gap of different rainscreen systems, and the effects that real life installation has on thermal performance.

Our white paper covers:

  • The effects of compression on thermal pads
  • Avoiding conservative predictions and assumptions
  • Post occupancy evaluation (POE)
  • Adjusting U-values to account for rainscreen subframes

For more information about SFS and NVELOPE® Thermal Solutions, please visit: www.nvelope.com

 

Simon Fielden

Sales Director

SFS

Tel:  0044 113 2085 500

uk.info@sfs.biz

www.sfsintec.co.uk

Twitter: @sfsintec

 

Please note: this is a commercial profile.

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