12 Feb 2021

Building Smarter Junctions

In this article, Sarah Viney of Marmox explains how some of a home’s trickiest technical challenges can be overcome with a surprisingly simple solution.

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Achieving compliance with the different parts of Building Regulations while keeping to cost and programme targets can be difficult enough for volume house-builders, let alone self-builders that are generally undertaking a unique development with a system they’ve only seen in YouTube clips or static displays at a trade show. Consider also that some of the key decisions to be made concern the narrowest lines on drawings, where different elements to the building envelope meet at potentially vulnerable interfaces such as the floor/wall junction.

The Building Research Establishment – or BRE – first highlighted their significance some three decades ago in a document unambiguously called ‘Avoiding Risks’, highlighting the extent to which heat is lost in such areas and the contingent problems which can result.

Since then, successive revisions to the regs have brought significant improvements to the performance of doors and windows and walls and floors. As is covered in the 16-page brochure on Marmox Thermoblock, up to 30% of total heat loss can occur at the junction between the latter pair.

Even more daunting in design terms is the fact that the Standard Assessment Procedure (SAP) penalises the use of insulation measures which have not been entirely thermally modelled, by applying a punitive ‘default figure’ within the calculations which can make it almost impossible for the building as a whole to achieve compliance.

It is imperative then to tackle what is often referred to as perimeter or linear heat loss at this junction while ensuring that your insulation measures do not compromise the capacity to carry the structure’s load above.

The ideal solution to this challenge is to utilise a composite product around the floor/wall junction, which provides both strength and excellent energy performance.

Another consideration for self-builders is that the solution should be straightforward to understand and install, either for themselves or their groundworks contractor, many of whom are unlikely to be fully conversant with the many different practices encompassed by modern methods of construction.

Again, you want a quick and straightforward product to fit in normal British weather conditions, which is equally suited to either masonry builds or the various types of timber and other framing systems. Importantly, it should ensure good continuation between the footings and blockwork or alternative structure above.

By utilising a suitable solution, all of these challenges can be addressed simultaneously: satisfying building control and budgetary and programme constraints, while preventing the very real problems that can result when linear heat loss does occur.

For around what is otherwise a well-insulated building envelope, the occurrence of cold bridging encourages condensation to form on the wall’s inner face or even interstitially. Inevitably such damp problems will lead to degradation of plasterwork and interior finishes and unsightly mould growth, which can have the most severe effect on indoor air quality, exacerbating such conditions as asthma. Therefore, it is vital at the earliest stage of planning your project to consider not just what main building methods you wish to adopt, but also how you will unite the different elements successfully.

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