ATJULY- AUGUST2010 23 aesthetic we were trying to achieve. We have since seen it used on some interesting small scale housing projects throughout the highlands and islands. The sheets are supported on 75 x 50mm timber purlins which are fixed through the counter batten to the roof panels. Lead valley gutter are formed at the roof verges and overlapped by a PPC aluminium verge capping. PPC aluminium ridge flashing sections will also be used. As mentioned previously each unit contains rooflights above the living room. For these we are using Fakro triple glazed rooflights, which achieve a u- value of 0.9W/ m ² K and were the best thermally performing rooflights available. Windows and Doors Triple glazed/ sealed Internorm Edition PassivHaus Aluminium Timber Composite windows and external doors, which achieve a 0.71W/ m2K U value, were supplied by Dynamight Internorm in Rosyth. The windows are manufactured in Austria and while it's unfortunate that we couldn't source anything with such a good U- Value or indeed PassivHaus certification any closer to home, we felt that with such critical elements we had to use a tried and tested product that was also PassivHaus certified. Ventilation Dynamight are also supplying the Passivhaus certified PAUL atmos 175 DC heat recovery units. The units utilise a balanced mechanical ventilation system withheat recovery system ( MVHR) with 88% efficient heat recovery - this helps reduce heating bills but just as importantly provides cleaner, fresher excellent quality of indoor air, free from pollutants, distributed using 100- 125mm diameter ducting within the first floor and loft floor cassettes. This makes the internal environment ideal for allergy or even asthma sufferers( ongoing research into the benefits of the Passive House concept and asthma sufferers supports this). It is also important to say, however, that home owners can still open windows if they want to - the MVHR will still recover heat from the exhaust air. Heating Predominantly through solar gains, internal gains and recovered heat with a small back up in the form of a wet heated towel rail system in the bathrooms ( supplied by an air source heat pump), which from our calculations and simulations is unlikely to be required to meet any of the primary heating demand. DHW comes from an un- vented hot water cylinder served by an ASHP system as the primary source of heating and a backup electric immersion heater. Conclusion With most Passive House projects to date seemingly restricted to one- off self build projects ( other than at Dunoon built by Fyne Homes Housing Association), it appears that the model is not yet attractive enough to the developer driven residential market in Scotland or indeed the UK as a whole. We believe, however, that with increased understanding and potential larger scale Passive House developments ( where repetitive elements may be increased), it may be possible to reduce the costs of passive house construction within the affordability envelope of developer housing, of course perhaps relying on an increased market value for a better quality housing product. Zero Carbon may be the new black, but can Passive House be the new green?

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