Passivhaus Object Documentation Plot 11 Ravenscroft, Tye Green, Wimbish, Essex, CB10 2FW United Kingdom. Project ID 2352 Project Designer: Chris Parsons, Parsons + Whittley Architects, www.parsonswhittley.co.uk Plot 11 is a 3 bedroomed house and one of 14 rural affordable houses for Hastoe Housing Association, built to Code for Sustainable Homes Level 4, consisting of: 6 No. 1 bedroom flats 5 No. 2 bedroom houses 3 No. 3 bedroom houses U-value external wall U-value floor U-value roof U-value windows Heat recovery 0.107 (W/M 2 /K) 0.091 (W/M 2 /K) 0.078 (W/M 2 /K) 0.79 (W/M 2 /K) 91% efficient PHPP Annual heating demand in kwh/m 2 /a 15 PHPP Primary Energy Demand in kwh/m 2 /a 104 Pressure test (n 50 ) 0.46 Parsons + Whittley Architects 1 Wimbish Passivhaus
2.2 Short Description of Construction: These properties are built using 190mm thick thin joint aircrete blockwork constructed off a reinforced concrete slab that sits upon 400mm of XPS insulation. The walls are clad externally with 285mm EPS insulation which receives a 16mm polymer modified render. Roofs are traditional pitched roof trusses with 500mm mineral wool insulation laid flat at ceiling joist level, utilising a dropped ceiling chord to achieve a thermal bridge free eaves detail. Air tightness is generally provided by a wet plaster system and specialist tapes at junctions. Windows and doors are triple glazed and installed within an insulated reveal to minimise thermal bridging, and made air tight with appropriate specialist tapes. Penetrations were minimised by the use of free standing external porch frames to receive services, letter boxes and meter cabinets, with service penetrations generally underground and sealed with specialist grommets. 2.3 Pictures of elevations Front elevation of Plot 11, showing freestanding porch which supports meter boxes and post box, all avoiding a thermal bridge. Side elevation. Rear elevation showing brise soleil General view of the site Parsons + Whittley Architects 2 Wimbish Passivhaus
2.4 Pictures of interior 2.5 Cross Section This drawing illustrates the general arrangement of all the major components including illustration of the thermal junctions. The red line indicates the air leakage barrier position. Parsons + Whittley Architects 3 Wimbish Passivhaus
2.6 Floor Plans These plans also comply with the UK design standards for dwellings funded by the Homes & Communities Agency, as well as the following standards: Secure By Design Lifetime Homes Housing Quality Indicators Code for Sustainable Homes Level 4 Hastoe Housing s Design Brief Parsons + Whittley Architects 4 Wimbish Passivhaus
2.7 Construction Details: 2.7.1 Floor to wall base detail This wall base detail avoids a thermal bridge by floating a 300mm concrete floor slab on top of structural insulation, which subsequently links to the external wall insulation as shown. Wall base prior to insulation The protruding concrete slab edge was, in the event, unnecessary and caused some placement issues. 2.7.2 Wall Junctions This detail shows the cavity party wall extending through the break in the elevation and shows how continuity of insulation was achieved. Parsons + Whittley Architects 5 Wimbish Passivhaus
2.7.3 Eaves Details The eaves overhang was designed to provide additional shading and help prevent overheating. Note how the bottom chord of the truss is dropped to allow the installation of 500mm ceiling insulation to join with the roof insulation. This photograph shows the wall insulation, ( grey EPS) extending between the rafters and through the soffit so as to form a thermal bridge free junction with the ceiling insulation. It was necessary to position this insulation in advance of the remainder of the wall insulation because the contractor wanted to complete the roof works in advance of applying the remainder of the wall insulation. 2.7.4 Window installation details The window jamb detail indicates how the insulation wrapped around it to reduce a linear thermal bridge and achieve a satisfactory Psi value. Note the brackets fixing the window back to the block work, and the factory fitted air tightness tape. Parsons + Whittley Architects 6 Wimbish Passivhaus
2.7.5 Typical air tightness details Parsons + Whittley Architects 7 Wimbish Passivhaus
2.7.6 Ventilation Duct Layout FIRST FLOOR The ventilation ductwork was contained within space joists at first floor level and insulated as shown. The ducts were largely distributed within the first floor zone and rose through risers at first floor level to avoid the need for a service zone at first floor ceiling level. GROUND FLOOR Parsons + Whittley Architects 8 Wimbish Passivhaus
2.7.7 MVHR and heater installation The MVHR unit was positioned in a dedicated cupboard near the front door, within the thermal envelope and mounted on an external wall The intake and exhaust ducts were taken out through the external wall. An electric inlet pre-heater was installed and a wet system coil heater applied to the supply air duct for heating when required. Paul Focus 200 MVHR unit Towel radiator for drying and heating Intake & Exhaust external grills In line duct heater radiator for heating Parsons + Whittley Architects 9 Wimbish Passivhaus
2.8 PHPP Results The maximum space heating and cooling was largely achieved through the provision of highly efficient fabric elements. It was discovered that these needed to be efficient because the UK builds particularly small houses and this made the PHPP targets difficult to achieve, hence the excessive U values that were achieved. Air Tightness was generally achieved at the first attempt although particular attention to this element was necessary as the target was felt to be challenging. Whilst wet plaster and appropriate tapes were able to deal with 95% of the issues, the use of timber floor joists caused significant difficulties in forming continuity between ground and first floor. The Contractor purchased his own blower door and undertook frequent interim tests to improve techniques and understanding of air tightness issues. Overheating Risks were managed on this project by the introduction of large eaves overhangs, brise-soleil at ground floor and external blinds at first floor level. The brisesoleil is designed to passively shade the large south facing windows during summer but allow warm sunshine through in the cooler seasons when the sun is lower. Parsons + Whittley Architects 10 Wimbish Passivhaus
2.9 Construction Cost per treated floor area: The construction costs for the complete scheme came out at 1,769/m2 or 2,057/m2 (based on current exchange rates) includes for all construction and services costs. 2.10 Costs for the Building The total final cost for the whole project, including all site based costs totalled 1,675.000 ( 1,947,696). Cost per Gross Internal Floor Area, (The normal UK floor area measurement) were equal to 1,652, ( 1,920) 2.11 Year of Construction: The project commenced on site in March 2010 and completed in June 2011 2.12 Architectural Design: The design of the scheme was largely driven by a consideration of the context of the site and an appreciation of the typical vernacular style of the site and locality. The settlement largely comprises plain fronted houses under simple natural slate roofs, and this context led us to consider a rendered finish under plain simple roofs. The economic solution of externally applied insulation was therefore possible within the local vernacular. Strong render colours are also a feature of that part of Essex and these were used to lift the properties. Colours were chosen with a similar tonal balance so as allow the properties to settle into the landscape without competing with each other. East-West orientation was employed so as to profit from passive solar gain and the houses arranged so as the private gardens benefitted from this private solar space. Internal layouts were then adopted to provide the primary living rooms on the south side and limit north facing openings to less important spaces such as bathrooms and entrance halls. 2.13 Building Services Planning: The client insisted that each house should have individual systems under the control of the individual tenant and this prohibited consideration of communal systems. Whilst solar thermal hot water was possible, this was not sufficient and so a small gas boiler was incorporated into each property. The solar thermal panels and gas boilers both provide heat to a 210l thermal store which is used to provide domestic hot water and occasional top-up heating to the incoming air supply. MVHR utilises a Paul Focus unit of varying size dependent on the unit size, mounted on an external wall with sound attenuated ducting to distribute fresh air into the living and sleeping spaces, with extract ducts from kitchens and bathrooms. 2.14 Structural Physics - Not Applicable 2.15 Structural Analysis Not Applicable Parsons + Whittley Architects 11 Wimbish Passivhaus
2.16 Experiences: The properties have now been occupied for 6 months and we provide a monthly seminar on site for other interested clients and architects. This gives us the opportunity to speak regularly to the tenants. One tenant of a 3 bed house with 4 children is overjoyed with her house and has reported that her first 6 months gas fuel bill, which provides all space heating and domestic hot water has been 30 ( 35). All the other tenants are reporting similar experiences varying only with lifestyle choices. 2.17 Studies The properties are subject to a complete technical monitoring by the University of East Anglia using remote meters and sensors sending information direct via a private broadband connection. We await detailed usage reports. Parsons + Whittley Architects 12 Wimbish Passivhaus