VIEWPOINT
ENERGY EFFICIENCY AND HOW TO ACHIEVE IT
Chris Stanley, Housing Manager at Modern Masonry: energy efficiency in the home isn’t just about the heating.
A
s an interesting article on the housing of the future by the Energy Saving Trust recently stated, we have seen an incredible transformation in terms of energy use in the home during the last century. In the last decade, the digital revolution has further accelerated the speed of change. Now we have futuristic tools such as smart meters at our disposal, and low-carbon energy is no longer unusual in a domestic setting. It’s also reassuring that according to an earlier survey by the same trust, Connecting with homeowners: making energy efficiency relevant (2016), most of those polled (nearly 90%) had completed some form of home improvement that included an energy efficiency upgrade. We can therefore feel relatively confident that public awareness around the topic is growing.
But before we get over-excited about what futuristic gadgets we can improve our homes with, we should consider the great impact the building materials of the shell have. It may not be as sexy as new technology, but it’s essential to understand the importance of the fabric of the building and the way materials are specified.
Merchants matter Builders’ merchants are key in helping homeowners and landlords make informed choices to improve the energy efficiency of their property. A solid understanding of energy efficiency helps building merchants recommend and supply the most appropriate materials available for a particular build. Energy efficiency affects everything from personal wellbeing to energy bill levels. Step one in reducing the energy needed for heating or cooling is always a high-performing building
envelope. The necessary ingredients for this are the right insulation, appropriate glazing and windows, solid airtight construction and minimisation of thermal bridges. The shape and orientation of the building also has an impact, but depending on the site, being flexible is not always an option.
There is, however, a threshold over which airtightness should not be pushed. A certain air change rate is necessary for good air quality and moisture control. As the Energy Savings Trust piece concedes, it’s a delicate but essential balance; we have to consider natural energy gains from people, appliances and the sun to rule out overheating.
This is where ventilation comes in, after the building envelope has been addressed. The different options for high-performance controlled ventilation include passive stack ventilation (PSV), mechanical extract ventilation (MEV) and mechanical ventilation with heat recovery (MVHR). The future will see the introduction of smart ventilation controls to manage the system we opt for. These help minimise energy wastage by reducing the energy thrown away with extracted air.
Thermal bridging
New build housing has come a long way over the last 25 years when it comes to energy efficiency. Successive changes to Approved Document Part L has ensured this. In practical terms, this has been achieved through improved airtightness and better insulation of floor, wall and roof elements. Thermal bridging, however, remains something of a problem. Typically a break in insulation, a thermal bridge occurs along the line of intersection between elements, adding to heat loss. They also appear in places where an element
with a higher thermal conductivity, for example timber, penetrates the insulation. Significantly, the adverse effect of a thermal bridge is heightened the better the building’s insulation is elsewhere in the structure. Therefore greater attention needs to be paid to this during the planning stages of a build; a thermal bridge can cause up to 30% of a building’s heat loss.
Designers and developers will of course endeavour to comply with Part L in the most economic way practicable. Many of our CBA accredited manufacturers supply thermal bridging details to help reduce the overall cost of a build. However, we want to ensure everyone in the supply chain is up to speed on the fundamentals to achieve optimal energy efficiency.
Using thermal bridging (Psi) values that have been calculated for specific details is essential. Armed with an understanding of this, builders’ merchants will be able to assist their customers in selecting the right product. The details and corresponding independently- calculated values for masonry construction are available on the CBA website.
Free online U-value calculator To ensure the building envelope is high- performance and delivers the above, we need to understand what U-value (thermal transmittance) can be achieved and how. Finding the appropriate U-value is imperative to be certain that a house is sufficiently energy efficient. The calculation can be challenging and complex, but they are necessary.
At the end of last year, CBA launched a simple, free-to-use online U-value calculator. It gives accurate results and assists in identifying this critical number. Aimed especially at those unfamiliar with the calculations, it is easy to use, and provides an excellent starting point, even if more detailed calculations prove necessary. Benefiting the wider construction and housebuilding industry is one of our core values at The Concrete Block Association. Therefore we’re always researching to find new solutions and tools to meet this aim. Our calculator is just one example of our efforts to meet the ever-increasing demands and guidelines from builders’ merchants across the UK. BMJ
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www.buildersmerchantsjournal.net July 2019
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