The case for Centres of Excellence in sustainable building design
The case for Centres of Excellence in sustainable building design
The case for Centres of Excellence in sustainable building design
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Lessons from Elm Tree Mews<br />
In 2005, <strong>The</strong> Joseph Rowntree Foundation commissioned, Elm Tree Mews, a<br />
small development <strong>in</strong> York aim<strong>in</strong>g <strong>for</strong> “an exemplar <strong>for</strong> 21st Century suburban<br />
homes”. <strong>The</strong> properties cover the full spectrum <strong>of</strong> hous<strong>in</strong>g types from threeand<br />
four-bedroom houses, to one- and two-bedroom apartments.<br />
<strong>The</strong> construction and subsequent occupation was monitored by Leeds<br />
Metropolitan University [Bell et al 2010b]. <strong>The</strong>se studies revealed that,<br />
although the project sought to achieve a standard equivalent to the<br />
Government’s carbon emissions target <strong>for</strong> 2013, the per<strong>for</strong>mance achieved<br />
was only marg<strong>in</strong>ally <strong>in</strong> advance <strong>of</strong> 2006 regulations. <strong>The</strong> measured carbon<br />
dioxide emission was 6.4 tonnes per annum compared with the 2.7 tonnes<br />
predicted <strong>in</strong> the <strong>design</strong>. In 2010 the foundation published “Low Carbon<br />
Hous<strong>in</strong>g - Lessons from Elm Tree Mews” to allow the <strong>in</strong>dustry to learn from<br />
their experiences.<br />
<strong>The</strong> problems experienced were primarily due to a lack <strong>of</strong> consistency<br />
between the thermal modell<strong>in</strong>g calculations and the actual <strong>design</strong> and<br />
construction <strong>of</strong> the build<strong>in</strong>gs. <strong>The</strong> calculations underestimated the amount <strong>of</strong><br />
timber fram<strong>in</strong>g <strong>in</strong> the construction and failed to account <strong>for</strong> thermal bridg<strong>in</strong>g<br />
or heat loss via the cavity party walls. As a result the fabric heat-losses were<br />
54% higher than predicted. Furthermore the measured air leakage <strong>for</strong> the<br />
completed properties averaged 7m 3 /h.m 2 , more than twice the leakage rate <strong>of</strong><br />
3m 3 /h.m 2 specified <strong>in</strong> the brief and used <strong>in</strong> the energy calculations.<br />
Further problems occurred due to the lack <strong>of</strong> a cha<strong>in</strong> <strong>of</strong> custody <strong>for</strong> energy<br />
per<strong>for</strong>mance throughout the <strong>design</strong> and construction. This meant that, <strong>for</strong><br />
<strong>in</strong>stance, the energy impact was not evaluated when an alternative w<strong>in</strong>dow<br />
supplier was selected with a lower per<strong>for</strong>mance than that orig<strong>in</strong>ally specified.<br />
F<strong>in</strong>ally, the heat<strong>in</strong>g <strong>design</strong> relied on a communal ground source heat pump<br />
system. It appears that the heat pump was not properly <strong>in</strong>tegrated with<br />
the conventional heat<strong>in</strong>g and hot water systems <strong>in</strong> the dwell<strong>in</strong>gs and this<br />
resulted <strong>in</strong> overall per<strong>for</strong>mance some 30% below the rat<strong>in</strong>g assumed <strong>in</strong> the<br />
<strong>design</strong>. <strong>The</strong> Foundation concluded that if the development had <strong>in</strong>stead<br />
been heated with ord<strong>in</strong>ary gas condens<strong>in</strong>g boilers, carbon dioxide emissions<br />
would have been about one tonne per annum lower.<br />
<strong>The</strong> report concluded that many processes and cultures with<strong>in</strong> the <strong>in</strong>dustry and<br />
its supply cha<strong>in</strong> need to change if zero carbon hous<strong>in</strong>g is to become a reality.<br />
• Design processes should be improved so that they:<br />
• take a much more rigorous approach to detailed <strong>design</strong> <strong>in</strong>clud<strong>in</strong>g<br />
undertak<strong>in</strong>g and check<strong>in</strong>g thermal calculations,<br />
• focus on as-constructed per<strong>for</strong>mance tak<strong>in</strong>g <strong>in</strong>to account the<br />
<strong>in</strong>teractions <strong>of</strong> the different components <strong>in</strong> both fabric and systems,<br />
• give more consideration to the needs <strong>of</strong> householders and provide<br />
controls that are <strong>design</strong>ed <strong>in</strong> accordance with ergonomic pr<strong>in</strong>ciples.<br />
• Services <strong>design</strong> should focus on whole system per<strong>for</strong>mance.<br />
• <strong>The</strong> plann<strong>in</strong>g and control <strong>of</strong> construction needs to be improved and<br />
<strong>in</strong>clude <strong>in</strong>-production test<strong>in</strong>g.<br />
• Improvements are required <strong>in</strong> services commission<strong>in</strong>g, test<strong>in</strong>g and<br />
monitor<strong>in</strong>g to ensure effective per<strong>for</strong>mance.<br />
• More support and guidance is required across the house-build<strong>in</strong>g <strong>in</strong>dustry.<br />
• Policy aspirations will not be achieved without rigorous evaluation <strong>of</strong> low<br />
carbon schemes and ensur<strong>in</strong>g that lessons are embedded <strong>in</strong> all parts <strong>of</strong><br />
the <strong>in</strong>dustry.<br />
24 <strong>The</strong> Royal Academy <strong>of</strong> Eng<strong>in</strong>eer<strong>in</strong>g