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How to combat thermal bridging

What are thermal bridges and where do they occur?

Thermal bridging is an important part of building design and performance, and is a crucial issue in compliance with Part L of the Building Regulations. However, despite the fact that thermal bridging is often discussed among designers and builders alike, the reality on the ground is that the industry lacks a deeper required understanding of what thermal bridging really is, what determines the extent of a thermal bridge, and how to design and build in order to reduce its effects.

No building is thermal-bridge free.

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Thermal bridges exist in all locations where either the building fabric changes shape (i.e. where one fabric element meets another at any junction due to the form of the building), or where the otherwise uniform heat flow through the fabric is interrupted due to an object penetrating the fabric at any point, such as structural beams sitting on blockwork, which may or may not penetrate the insulation layer.

In Ireland and the UK, methods of building measurement for the purpose of carrying out a Building Energy Rating (BER) assessment also affect how a linear thermal bridge in quantified.

In mainland Europe, many countries measure the building envelope externally for the purpose of BER rating. This means that at all outward-facing junctions (e.g. eaves, external wall corners, ground floors etc.) there is an overlap in the measurement of element areas.

From an accountancy point-of-view, the job of the thermal bridge assessment is to measure this overlap and correct it. This is the reason that many thermal bridges quoted in European or Passive House documents are either very low or even negative values. In Ireland and the UK however measurement of the building is done internally. This means that at all junctions there needs to be a gap in the measured thermal envelope. In this case, the job of the thermal bridge assessment is to measure the gap and fill it. This normally creates a relatively large positive value, as in energy-accountancy terms there is a hole to fill.

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Thermal bridge values are affected by the shape of the building, the materials within a junction and how they are assembled, as well as the convention for measurement of the building. For the latter reason particularly, thermal bridging can attribute quite a large percentage of overall measured building fabric heat loss. So how can this be reduced?

Let’s not re-invent the wheel…just use a different tyre….

In Ireland, standard construction follows the forms of common build types illustrated in the Acceptable Construction Details (2011, www.environ.ie). Of these, the most common forms are cavity wall construction, hollow block, externally-insulated masonry, timber frame, as well as various combinations of the above with internal insulation. Steel frame housing is still less common than the aforementioned methods.

One of the benefits of having standardised forms of construction is that all members of the industry are well-versed in their application, from site to design office and everywhere in between. In order to best suit the market, the Quinn Lite block range is a
vailable in most industry-standard block sizes. This means block-layers can readily insert a Quinn Lite block at key locations in the building envelope without having to think twice about any special considerations in its application.

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Compared to a standard block (2,000kg/m3, thermal conductivity value 1.33W/mK), the Quinn Lite block range comes in the Super, Standard and Seven ranges, with thermal conductivity between just 0.12W/mK and 0.19W/mK, and dry density of between 480-760kg/m3.
This means that by using Quinn Lite the building can achieve over 90% reduction in heat loss through the block while weighing over 75% less than standard blocks.
Therefore, not only does Quinn Lite ensure superior building performance, but will also result in significant savings in labour time on site due to faster laying times.
By using Quinn Lite blocks at junctions means faster build times, lower heating bills for occupants, potential savings in heating and renewable energy plant, improved energy performance values and reduced carbon emissions. In addition to this, occupants will experience a healthier, more comfortable environment. And Quinn Lite blocks adhere to building regulations Part L compliance.

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For futher details of the Quinn Lite blocks and how to combat thermal bridging contact the Quinn Technical Team on 08000 322 122 or 18000 322 133.