The following text and images were provided by the architect, Phil Bixby of constructive individuals
Fulford PassivhausSee more on the Passivhaus standard. The PassivHaus Institute has pioneered a standard for low energy buildings. It includes very low energy usage and ways of achieving this. The word is derived from the idea of buildings which are fundamentally low energy and passive solar heated rather than using extra gadgets to heat them. See Passivhaus for the UK branch of the organisation.+ was built for, and with, clients Karin deVries and Rob Aitken, culmination of a lengthy process of design which began with proposals to extend their existing home and finished with a completed new-build project which eliminated the compromise (and VATValue added tax can, to a large extent, be reclaimed on self build. see the page on VAT) of the extension proposals.
Demolition of the existing poor-quality structure left a spacious site with a southerly outlook. The design approach was deliberately simple – a three-storey[for the purposes of part B (fire) of the Approved Documents to the Building Regulations] this includes - (a) any gallery[for the purposes of part B of the Approved Documents] - A raised area or platform around the sides or at the back of a room which provides extra space. if its area is more than half that of the space into which it projects; and (b) a roof, unless it is accessible only for maintenance and repair. house of simple rectangular plan, with the upper storey largely within the pitched roof. The roof itself is offset to increase the south-facing area, which hosts a 9.8kW PVPhoto Voltaic. referring to the generation of electricity from sunlight array. This contributed towards the house being certified as Passivhaus PlusA somewhat higher standard than Passivhaus standard with a lower limit for renewable primary energy demand and also a requirement to generate renewable energy on site (or if not possible then investment in off-site generation). (see more at Passivhaus Standard) – the first in the UK.One of the largest challenges with the project was building to Passivhaus standards – and incorporating a substantial renewables system – while keeping as far as possible within “conventional” build costs. This led to a lengthy refinement of the construction system, working in partnership with contractor Transcore. Original proposals for a deep-section timber frame building envelope were replaced by a cheaper – but more complex – wall construction comprising cavity construction of timber frame inner leaf, rendered blockwork outer leaf and various layers of insulation. Likewise the roof construction ended up with more layers than originally anticipated due to cost constraints limiting joist depth. The construction method had knock-on effects on the substructure; originally a fairly simple-looking raft with a perimeter strip was envisaged, but the use of a very conventional timber frame meant that point loads required additional pad supports, and as a result the foundations became more complex.
The final main impact of the cost constraints was that the contract with Transcore was limited to the weathertight shell, and completion of the house (joinery and decoration) and service installations were undertaken on a direct labour basis by the clients. The design had always incorporated service voids inboard of the structure and airtightness layer, but there were still some issues around separation of the “contract” and “post-contract” works.
The main structure went together without major problems. The contractor worked with the client – who was very hands-on on site – to ensure cold-bridging was minimised using the multi-layered approach to insulation. Likewise airtightness was a constant focus, and despite one or two issues with three-dimensional junctions an impressive final airtightness value of 0.41/hr was achieved, helped by input from airtightness guru Paul Jennings who carried out two additional intermediate tests.
The house was completed and occupied in the summer of 2015. As architect I was highly chuffed to see the sun striking the windows exactly where the 3D sunpath modelling had predicted that the overhanging roof and brise-soleil would put it. The clients are still in the process of installing heating – there was none at all until the 1kW post-heater in the MVHRMechanical Ventilation with Heat Recovery. This is usually a double fan arrangement which extracts stale air from the house and sucks in fresh air at the same time. As the warm stale air is blown out, heat is extracted from it and passed over to the cool incoming air by means of a heat exchanger. With the latest technology, over 90% of the heat can be recovered. (see Passivhaus standard) system was wired up in December, and it is planned to augment this with heated towel rails in the bathrooms. Monitoring is being set up to check the performance of the PV’s, DHWDomestic Hot Water. see the section on domestic hot water cylinder and immersion heaters.