Builders Book and roasting residents

November 8, 2016

Overheating

“So,” I hear you ask, “what is the connection between the Builders Book and roasting residents?” Well, if you’re asking…..

The Builders Book, you may recall, was published by the Zero Carbon Hub in 2015.  It is one of a suite of documents still publically available on their website that share knowledge and challenge existing practice. ‘Roasting residents’ refers to an article in the Times in May 2015, entitled ‘Residents roast in eco homes greenhouse effect’, which highlighted concerns about overheating in homes built to high standards of energy efficiency.  And this got me thinking.

If you look through the Builders Book, it has examples from live sites demonstrating how current practice means that a building becomes less likely to meet its design performance.  It is a practical, if alarming, outcome from their excellent work on the performance gap, and shows how we end up with buildings that consume far more energy than they were designed to.  The poor practice that the Book highlights has two main impacts;

  • It undermines airtightness, which in turn creates draughts. This isn’t ventilation, which is good, but infiltration, which is bad.  It creates a lower perceived internal temperature and consequently a higher setting on the thermostat.  It risks interstitial condensation as warm moist air leaks through cracks in the fabric and cools on the colder surfaces it meets.  But it does provide a level of air exchange.
  • It creates unplanned, additional heat loss. This requires more energy to counterbalance, and creates condensation and mould risks where thermal bridging creates cold spots.

Both impacts increase energy use, cost and risk to health and the building fabric.  They fundamentally mitigate against providing a comfortable home which an occupant can afford to heat at reasonable cost.

So, what is the connection with roasting residents?  Ironically, these impacts make a building difficult to overheat – so good site practice that builds a building properly means you are much more likely to get overheating, because Building Regulations are not very robust when it comes to the factors that prevent overheating; ventilation, and overheating risk assessment.  Reading the article, it feels like energy efficiency has taken a bullet for what is actually poor specification, design and site practice.

So what can you do?

  1. Recognise where Building Regulations are robust, and where they are weak. Where they are weak, your design teams may need to specify how you expect this be resolved.
  1. Upskill. You need to know enough to talk the language of Dwelling Fabric Energy Efficiency, energy demand, primary energy, heat load, psi-values, airtightness, default versuss calculated values…  This will underpin how you plug the gaps and how you work with your supply chain.
  1. Use your tender to draw out from contractors how they will deliver your specification and minimise the performance gap; because of your upskilling, you’ll know what should be coming back and what you’ll expect to see in their method statements.
  1. Bring in external support; the most ambitious, innovative housing associations continue to do this, even when they are familiar with challenging specifications. This is an investment in value, in your assets and your business, and moves you out of the space where your procurement is based on ‘build it to Building Regs at lowest cost’.

Ask any contractor and they will tell you that they can only price what you specify.  And building to Building Regulations isn’t necessarily a problem.  Delivered properly, it will give a structurally sound building with a relatively low level of energy demand.  But it won’t deliver this by default.  The client needs to be clear about their expectations and have the capability to ensure that the performance they want is delivered; in other words a comfortable home with low energy costs that doesn’t roast anyone.

 

Written by Tom Jarman. Tom is Environmental Sustainability Co-ordinator at Your Homes Newcastle.

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