PASSIVHAUS DEVELOPMENT 14 RESIDENTIAL UNITS, WIMBISH FOR HASTOE HOUSING ASSOCIATION
Passivhaus Development INTRODUCTION Deejak Builders and Passivhaus Design Solutions Ltd (PDS) are pleased to present this response to the proposal to construct 14 residential units to certified Passivhaus standards at Wimbish. We believe our combined proposal demonstrates a hallmark standard of thinking, development and implementation of energy efficiency within the construction industry. Deejak has a track record of long-term relationships with clients over more than 35 years and a strong leaning towards innovation in methods of construction, sustainability and environmental management. PDS is an international alliance of two UK and German leading edge architectural practices - Chambers Goodwin and Partners of Rickmansworth, Herts and r-m-p, architects and engineers, of Mannheim, Germany. Both long established firms have extensive expertise in Passivhaus development and design. This document demonstrates our professional expertise and familiarity with aspects of design for Passivhaus, identifies the critical cultural and management issues involved. It also contains a case study of Deejak’s development of low-energy homes at Wixams New Village, a new flagship development in Bedfordshire, a profile of the parties involved in this proposal and a description of our supply chain partners. Deejak Builders
Passivhaus Development PASSIVHAUS DESIGN AT WIMBISH When considering a Passivhaus project, the architectural design needs to incorporate specific and unique features from the earliest stage. This is particularly so when a development site is limited for space or its shape restricts building footprint and layout. It is necessary for an appointed design and build contractor and his professional advisers to have input into the initial scheme design to ensure the final detailed proposals will meet the specification and brief and adhere to Passivhaus standards. In this case, the exact nature of the two-stage process is not clearly defined and the contractual relationship and apportionment of risk is difficult to establish from the documents provided. In the case of Mill Road the detail of construction required for a Passivhaus building will not be a governing factor as the site appears to have enough room to accommodate the varied external envelope solutions. Consideration will need to be given to the building form, orientation and fenestration, and this will need to be taken into account at the planning design stage. The current scheme has the right orientation, but some work will be required to ensure the balance is provided to regulate solar gain. Window sizes will need to be calculated against the notional envelope construction and details. A preliminary Passivhaus software PHPP2007 calculation tool will be required to verify the design. In conjunction with a site appraisal shading from natural features such as trees and bushes will need to be considered as solar gains for the new buildings during winter months should be optimised to reduce the heating load requirement. This evaluation will directly impact on the size of glazed areas and in particular those facing generally south. A dwelling designed to Passivhaus principles is intended to generate as much of the heating/cooling of the building as possible minimising the input of imported energy. Deejak Builders
Passivhaus Development THE PASSIVHAUS BRIEF The invitation identifies the following as essential in Passivhaus construction:- • Mechanical ventilation and heat recovery • Air tightness • Thermal bridging • Component, build system and subcontractor selection • Quality control and management In addition we would identify the following specific requirements for Passivhaus design, which must be addressed holistically, while contained within the 5 principles above:- • Total energy demand for space heating/cooling less than 15kWh/m 3 /yr • Total primary energy use of all appliances, domestic hot water and space heating/cooling is to be less than 120kWh/m 3 /yr • Air permeability level 1m/h/m 3 or less • Windows with combined U-Value of 0.80 W/ m 3 /K or less • External building fabric (Floor, walls and roof) U-Value of 0.15 W/ m 3 /K or less As part of a value engineering exercise carried out in conjunction with the Passivhaus software, compatible off site panellised frames and more traditional construction will be evaluated for the project. These various systems might include:- • Open frame timber with added insulation • Close panel timber frame with added insulation • Solid wood frame with external insulation • SiPs close panel systems with added insulation or doubled panels • Stotherm mineral on lightweight block • Modcell straw with added insulation • Beco Wallform (or similar) hollow polystyrene interlocking block with concrete core • Formworks ICF (Styroframe) EPC/light gauge steel/ concrete core(VIP) system vacuum insulated panel with concrete or masonry structure • Brick and aircrete block cavity wall with full fill cavity insulation Deejak Builders
Passivhaus Development CONSTRUCTION Other constructional systems and materials are available to use in combination with the above or as alternatives. Each will have benefits and drawbacks. The most likely structural panel system to suit the project would be either a SiPs system or a solid wood frame. The use of solid wood on the continent has proven to be highly successful in achieving high levels of air tightness with reduced thermal bridging. r-m-p currently favour this form of construction on projects they are developing to meet the Passivhaus standard. The best means of achieving high levels of air tightness are when the on site components for the external envelope are kept to a minimum. If the design of the houses can achieve whole elevation/storey panels, the number of joints between the panels can be reduced removing the risk of onsite failure to seal joints correctly. Reduced joint numbers also makes it easier to check works to ensure the highest standards are achieved at joints. The use of off site manufacture gives an opportunity for the quality to be closely monitored in clean and controlled environments. If taped seals are required, it will be easier to carry this work out in a factory rather than on a dusty site. As part of his responsibility, the manufacturer will be required to deliver panels which meet the highest standards of air tightness, leaving only the jointing of subsequent components at a site level. Some panelised systems can even be delivered from the factory with windows fitted and glazed, thus ensuring the quality of air tightness for the whole panel. Panels can be interlocking and service wire ways can also be incorporated reducing the risks associated with random site cutting. While desirable in terms of quality these systems preclude late client changes such as additional power points. It will be important for the appointed contractor to work closely with his supply chain to ensure they are fully aware of the requirements to meet the high levels of air tightness. This can be reinforced through training and education of all the parties from the client to the operative at site level. The need to adhere to the design details, the self-checking of work and the close supervision by the contractor’s management staff both on site and through the supply chain is vital. A change of technique or method for a ‘good idea’ at site level could lead to failure to meet the requirement of a detail that has exhaustively been developed to meet a specific need in an individual location. As the buildings thermal resistance values increase, coupled with greater air tightness, then thermal bridging becomes more relevant and important. The ideal situation is the removal of all thermal bridges, but this is almost impossible to achieve economically. The important issue is to control thermal bridging, calculate the effect and compensate. Examples of detail can be provided to show how thermal bridging is reduced or mitigated. The designer will need to consider each of the thermal bridging situations as individual, and only use a common detail were this is appropriate, each of the individual thermal bridges will be calculated and inputted into the Passivhaus software. This coupled with the other data will be submitted to the Passivhaus Institute to obtain the Certification. Deejak Builders
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