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Fabric First and Renewables: What’s the right balance?

I was approached by Energist to produce a ‘guest blog’ looking at ‘Building Fabric versus Renewables’ so here’s my take on it… A well-designed energy efficient dwelling considers both fabric and renewables, but the fabric should always come first; once that solid base is achieved, correctly sized services and appropriate renewables can be considered. A well designed building fabric is one that that is well insulated, with carefully thought out junctions, with low heat-loss openings that can still take advantage of solar heat gains. It should have a good level of air-tightness, whilst maintaining adequate ventilation (ideally recovering extracted heat to pre-warm the fresh air brought in to replace it) and it should be designed to prevent summer overheating whilst not needing too much heating in the winter. New buildings are supposed to be (according to EU law) achieving zero carbon (and nearly zero energy) by 2021 and to do that, both a good fabric and renewables will be needed.

However, I’m not convinced as to how close to zero we’ll actually end up building in the UK. The regulations don’t yet require both good fabric and renewables in order to comply. The government advised in their Allowable Solutions consultation response, that the on-site requirements for 2016 for Low/Zero carbon new homes will be ‘Code 4’, which is 19% better than L1A 2013 target, so that will be the first time that designers will really start needing to consider both.

The introduction of a Target Fabric Energy Efficiency for L1A 2013 for England was a good step forwards, but one without enough teeth to influence changes in building practices.  The notional package used to set the fabric targets has a 15% relaxation, which allows a house to pass with a specification little different to 2006 standards from the elemental fabric point of view (better psi values, glazing and air tightness certainly, but roof, walls and floors not too dissimilar).

It’s a better situation than we did have however; for several years there were loopholes whereby the higher your demand for heating, the greater the benefit some technologies gave (CHP was the particular culprit there, with a higher heat demand, more electricity was generated, giving a better result), this effectively encouraged designing a poor building fabric. Heat Pumps also came out so well at one point, that designers could get houses to pass with worst case limiting values for pretty much everything else (due to the artificially higher target assigned to keep electric heating as a viable solution).

The fuel costs and carbon emissions of such fabric relaxed solutions were much higher than a better insulated, gas solution, but that loophole to compliance was enthusiastically seized on by some, buying in cheap heat pumps (largely not installed by competent installers) and going with a poorer fabric. Tighter fabric targets now ensure that the worst excesses and loopholes are closed off. There is no point building houses that have appalling energy efficiency and getting them to pass with bolt-on’s – that is not sustainability, it’s simply wasteful.

High performance technologies with a good fabric is very much the right way to go, and once we decarbonise the grid (and renewables are helping with this), we will need to wean ourselves off the gas and oil heating that we’ve become so used to. Heat pumps are very much the right solution for off-gas properties in the meanwhile; provided they are correctly sized and heating demand is reduced first. Much more potentially influential to building practices than the English requirements, is the new Welsh Part L, which instead of adopting the TFEE / DFEE calculation, just tightened the limiting standards instead. Fabric is thus front and centre at the heart of compliance, with lower heat demand the driver towards lower fuel costs and reduced emissions.

By taking a fabric first approach, developers can essentially ‘future proof’ their designs; a more energy efficient fabric from the outset can be upgraded down the line, through improved services, ventilation measures or the addition of renewable technologies. Upgrading a poor fabric can be trickier. Reducing the energy demand of a dwelling from the start limits heat losses through the building’s envelope over its entire lifetime; it is better to not need as much heat over a long period, than to compensate for a higher fuel demand. Compared to renewable technologies, fabric measures require little to no maintenance (excepting windows), with a considerably longer lifespan (to match the life of the dwelling); Many renewable technologies have a realistic lifespan of around 20 to 25 years if adequately commissioned originally and then correctly and regularly maintained. Some technologies will require part replacements over that period (e.g. inverters) to maintain efficiencies. Lack of understanding on the part of the technology commissioner or on the part of the user can also cause problems with technologies which may result in reduced benefit. With the fabric, it just does its job. Jonathan Ducker Jonathan Ducker is the Energy Assessment Manager for Kingspan Insulation Limited. He has an extensive knowledge of  energy efficiency, renewable energy systems and sustainability in buildings with an expert knowledge of the relevant  sections of each of the various UK building regulations and standards and their interactions with SAP. He provides  authoritative advice regarding energy assessments for a wide range of public and private sector clients. When nagged  enough he also writes occasional blog posts for http://blog.kingspaninsulation.co.uk/

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Stuart Clark

Author: Stuart Clark

This article was published by Stuart Clark on 18.09.2014.