Achieving Code Level Five with Concrete and Masonry

Transcription

1 Achieving Code Level Five with Concrete and Masonry A mainstream approach for high performance, low-cost social housing.

2 Achieving Code Level Five with Concrete and Masonry Since the introduction of the Code for Sustainable Homes in 2006, the housing sector has made good progress in developing solutions to meet its tough performance standards, at all levels of the Code. Going forward, the next challenge is bringing the lessons learned into mainstream housing, in a cost-effective and practical manner. For social housing this challenge is particularly demanding, since energy efficiency enhancements to the fabric and services must not impact on the core design requirements within this sector, which include: Affordability Low maintenance Simplicity (easy to operate) Use of systems with a proven track record Robust and durable solutions The RSL partner for this project is A2Dominion Group The A2Dominion Group is one of the country s leading providers of high quality housing. The Group now provides over 30,000 homes across London and southern England with thousands in development. It offers a wide range of housing options, including homes for rent, sale and shared ownership, as well as temporary, student, sheltered, supported and key worker accommodation. 2 Meeting the challenge

3 Meeting the challenge A design team, which included a Registered Social Landlord (RSL), A2Dominion Group, and a contractor, was established to develop an outline design and specification for a three-bedroom, five-person house compliant with Code for Sustainable Homes (CSH) level 5. The optimal 85m 2 design secures the maximum funding available in its band and is suitable for both mid and end-of-terrace plots, and could form part of an RSL s national programme of construction. The basis for collaboration on this project was recognition that both concrete and masonry solutions provide an effective way of meeting the specific design needs of social housing, and benefits from using mainstream construction methods supported by a well-established supply chain. For the purpose of the project, the plot was assumed to have a north/south orientation, low flood risk and relatively low ecological value. The design meets the RSL specific design and quality standards, and also complies with requirements of the Lifetime Homes and Secured by Design standards. This publication gives a brief overview of the key decisions taken, and lessons learnt by the design team in working up the plans and specification. Particular attention is paid to the thermal performance of the building fabric and the overall energy and CO2 rating, which can account for over a third of the total points available in the Code. Key findings The specification of conventional concrete and masonry construction presented no particular thermal performance limitations at code level 5, notwithstanding the need for larger cavities and enhanced measures to minimise cold bridging. (This point is also relevant for code level 6, because the difference between code levels 5 and 6 largely relates to the provision of renewable energy.) Many of the newer systems and technologies associated with code level 5/6 performance were discounted early on as they did not fit well with the particular needs for social housing i.e. for simple, durable, cost-effective solutions with a low maintenance requirement. The specified concrete and masonry construction elements attractedgood scores in the BRE Green Guide, which is used to assess the environmental performance of materials within the Code for Sustainable Homes. Most suppliers of concrete and masonry products operate environmental management schemes compliant with ISO (or equivalent). This attracts points in the Responsible Sourcing category of the Code. Further points can be scored by specifying materials from suppliers compliant with the new standard for responsible sourcing of construction products (BES 6001). The design exercise underlying this document highlighted that: The house building industry using concrete and masonry solutions can make the step change required to deliver zero carbon housing by Code level 5 homes built with concrete and masonry are affordable and scalable. Code level 5 homes built with concrete and masonry can use existing construction methods and skills with a simple renewable energy strategy. The local supply chain, short lead times and a flexible programme offered by concrete and masonry construction continue to be a key benefit. 3

4 Achieving Code Level Five with Concrete and Masonry The design team and process The RSL and its contractor partner appointed the design team which worked closely with their in-house team to develop a design that addressed the following objectives. 1. RSL objectives (taken from original brief) RSLs are currently funded on code level 3 and the next step in 2010 to code level 4 is relatively straight-forward with the use of small amounts of renewables and modest upgrade to the fabric. The timing of this proposal means that units could be delivered around the time that all RSL projects need to meet code level 4. It has therefore been decided that this project should aim to produce a house/apartment of code level 5/6. Code level 6 being mandatory by 2013 for RSL work. The design should aim to follow Lifetime Homes guidelines as well as other RSL design criteria (HQIs [1] etc) which are needed to obtain funding. To facilitate the management of rented units on a whole life basis, the build method should use traditional materials and skills that are readily available, robust and flexible, enabling alterations at a later date. The design should be traditional, both inside and out, allowing it to harmonise with the local vernacular. 2. What lessons did the RSL hope to learn? Whilst a date does not currently exist for the implementation of level 5, level 4 will be introduced in April 2010 and level 6 in April Housing Corporation funding is currently given on the basis of meeting the relevant mandatory CSH level. Part of this project will show (using current and simple technology) how a level 5 house might be achieved and at what cost. This evidence may then be used to support higher funding levels. The current house type used as a basis to develop the proposals is on the maximum size of its band for funding reasons but still lacks things like home office space. The design exercise aims to learn how to maximise the points scored through good design and to assess any additional costs arising. To understand design techniques and systems required to consistently reach an air tightness of 2m 3 /(h.m 2 ) will be essential for future build. Low build costs and repeatability are key requirements, ensuring best value for grant funding. The brief was defined by the RSL to meet current standards and address future energy efficiency requirements. 4 The design team and process

5 Brief summary Must have 1. Brick/block external walls. 2. HQI space standards. 3. Design Quality Standards (DQS) [2]. 4. Minimum level 5 Code for Sustainable Homes. 5. Traditional methods of construction and common trades. 6. Design layout and materials which could be used virtually anywhere. 7. Monitor costs and produce a completed product cost based on an imaginary site. 8. Finish and fit out as standard. 9. Reflect an end-of-terrace unit (approx. site area 8x4m deep) but also consider the affect when this unit could be used as mid-terrace. We have already learnt how easy it is to reduce the heat loss through the building through better insulation methods and the effect it has on the overall efficiency of the house and its running costs and we need to explore and optimise this. We need to understand and identify low-carbon technologies which are relevant to both new and existing housing, helping facilitate future upgrades and their management. To reflect on the legacy of the current stock, consider effective remedial solutions and ultimately consider its design life. Desirable but not essential 1. Three-storey house with no garage (three-bed, five-person). 2. Green Guide A grade construction materials. 3. Life Time Homes [3]. Items we might consider 1. 12V lighting system to reduce power consumption. With PV connection. 2. Grey water/rain water harvesting. Roles and responsibilities of the design team The role of the chosen contractor and their design team, code assessor and construction team was to develop and evaluate an RSL s standard house types for code level 5, that was cost-effective and buildable. The material selection was made by the RSL in conjunction with the housebuilder/design team to ensure that the brief was met within the constraints of the cost and buildability parameters. Best value for grant funding. 5

6 Achieving Code Level Five with Concrete and Masonry Street elevation: Ground floor: potential positions for wheelchair platform lift. Ground floor plan 6 The design team and process

7 Rear elevation: First floor: potential positions for wheelchair platform lift. First floor plan 7

8 Achieving Code Level Five with Concrete and Masonry Meeting level 5 of the Code for Sustainable Homes Figure 1 provides a summary of the anticipated performance in each of the Code categories. This reflects the credits that are likely to be achieved when designed as an end-of-terrace house on a typical site. The code category of primary relevance to the design team was Energy and CO 2 as this has specific implications for the choice of materials and method of construction. It also scores by far the greatest number of the available points, and for these reasons this category was the main focus during the design process (and this document). It is also the only section underpinned by regulation i.e. Part L of the Building Regulations. With the exception of the Materials category of the Code, the remaining points are less directly influenced by the method of construction. The environmental impact of the specified materials gained 4.5 of the 7.2 points available, scoring well for environmental performance with the external walls and roof achieving an A+, the windows scoring an A and the internal walls and floors achieving a B. All the materials could easily be sourced from suppliers operating an environmental management scheme (typically ISO 14001), which attracts half the points available in the Responsible Sourcing sub-category. However, since the completion of this project, a new standard for the responsible sourcing of construction products (BES 6001) has been introduced. Concrete and masonry material sourced from suppliers meeting this standard will score full points for responsible sourcing. Energy & CO2 (Code Category One) A key outcome of the design process was that the specification of conventional concrete/masonry construction presented no particular thermal performance limitations at code level 5, albeit larger cavities are required and enhanced measures are needed to minimise cold bridging. Whilst not part of the Code, the heavyweight approach has the added energy efficiency benefit of enabling a wet plaster finish to be used, which provides a simple, durable means of ensuring long-term air tightness and also increases the thermal mass of the walls (details of the construction elements are provided on page 11). 1. Dwelling Emission Rate (DER) The Target Carbon Dioxide Emission Rate (TER) for the house was calculated to be kg/m 2, and to achieve level 5 of the Code this had to be completely offset. i.e. a Dwelling Carbon Dioxide Emission Rate (DER) of 0 kg/m 2 or lower was required. The final design produced a DER of kg/m 2 which is an improvement of 101 per cent. This scores 14 out of a potential 15 credits. 2. Heat Loss Parameter (HLP) Credits are available in the non-mandatory part of the Energy category for a low HLP (1 credit for an HLP smaller than or equal to 1.3, increasing to 2 credits for a value of 1.1 or lower). The house achieves an HLP of 0.81, scoring the full 2 credits. ENERGY & CO2 96% HEALTH & WELLBEING 83% LAND USE & ECOLOGY 56% Figure 1: Code for Sustainable Homes - percentage category scores MANAGEMENT WATER MATERIALS WASTE 62% 100% 100% 100% POLLUTION 75% SURFACE WATER RUN-OFF 100% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Category Score a % of Maximum Available Code level 5 was set by the RSL to confirm the ongoing viability of concrete and masonry construction 8 Meeting level 5 of The Code for Sustainable Homes

9 3. Internal lighting The specification required 75 per cent or more of the lighting installation to comprise low energy fittings/lamps, attracting 2 credits; the maximum available. 4. Drying space A rotary dryer in the garden was specified, attracting 1 credit which is the maximum available. Whilst incurring additional cost, an alternative option for sites with a favourable orientation is to add a lobby/sunspace which could double as drying area and would also improve the dwelling s thermal performance (see passive solar design below). 5. Eco-labelled white goods The specified dishwasher and washing machine are both A rated under the EU Energy Efficiency Labelling Scheme, and the fridge/freezer has an A+ rating, jointly achieving the maximum score of 2 credits. 6. External lighting At the design stage assessment of the Code, no points were included for external lighting. It was considered relatively simple to add external lighting later if additional points were deemed necessary during the construction phase. 7. Low or zero carbon energy technologies 27m 2 of Photovoltaics (PV) is specified for the south facing area of the roof. This provides around 3kW of peak electrical output, reducing CO 2 emissions by more than 15 per cent, which achieves the maximum score of 2 credits. 8. Cycle storage The provision of a timber shed for the storage of three bikes (which corresponds to the number of bedrooms) attracts the maximum score of 2 credits. 9. Home office Provision has been made in the layout of one of the smaller bedrooms for a home office, gaining the maximum score of 1 credit. It has been designed to meet code requirements for a quiet, well-ventilated space with a minimum wall length of 1.8m for a desk, chair and filing cabinet. Thermal mass Whilst thermal mass does not fall within the scope of the Code, making use of it was nevertheless an important design requirement, particularly as it is an inherent property of heavyweight construction. Its key function in the design is to reduce the risk of summertime overheating and provide a degree of adaptation to our warming climate. It also has the potential to improve the energy efficiency of the dwelling during the heating season through its ability to store and release solar gains and heat from internal sources. This is influenced by orientation and window location/size, and is currently outside the scope of the SAP tool used to calculate the thermal performance of dwellings. However, revisions to SAP currently underway are likely to address this issue, potentially enabling a modest improvement in the energy/co 2 rating for dwellings that take advantage of their mass. The provision of thermal mass was one of the factors considered in the selection of materials and finishes, and was assessed in terms of admittance. This is effectively a measure of effective thermal mass; with admittance values around 1 W/m 2 K being low and values of around 4W/m 2 K or more considered to be relatively high. The values achieved for the specified construction elements are shown in Figure 2. External walls: Medium density aggregate block inner leaf (1400 kg/m 3 ), wet plaster finish. Admittance value: 4.2 W/m 2 K. Internal Walls: Ground floor: Upper floor: Medium density aggregate blocks (1400 kg/m 3 ) exposed both sides, wet plaster finish. Admittance value: 3.7 W/m 2 K. Concrete beam & block. 90mm of screed on insulation, tiled finish. Admittance value: 4.0 W/m 2 K. Concrete beam & block. Finish: carpet/lino on 75mm screed. Ceiling to first floor: plasterboard on battens. Approximate admittance value for top and bottom surfaces W/m 2 K Figure 2: Admittance values for key construction elements Surface finish - walls A wet plaster finish for both the internal and external walls ensures the inherent thermal mass in the concrete blocks is fully utilised. The thermal conductivity of the plaster is similar to that of the blocks, helping maximise heat flow back and forth between the room and walls. The use of plaster increases the wall s admittance value by around 1.4 W/m 2 K compared to the usual alternative of plasterboard on dabs. Others drivers for a wet plaster finish were air tightness, durability and resistance to flood damage. Surface finish ground floor Whilst the thermal mass contained in the beam and block floor is isolated by the insulation located above it, there is still a useful amount provided by the screed and tiled surface. The choice of a tiled finish was driven by a combination of: compatibility with underfloor heating, increased mass, durability and resistance to flood damage. Passive solar design Plots with a favourable orientation and minimal overshadowing could potentially benefit from the addition of a lobby/sun space. This would provide a thermal buffer, reducing heat loss from the adjoining wall and improve energy efficiency during the heating season, particularly in the spring and autumn when its contribution to the space heating will be at its greatest. The minimum floor area could be that needed for a drying space and cycle storage. 9

10 Achieving Code Level Five with Concrete and Masonry Summary of detailed specification Roof structure: A+ rated timber trussed cold roof construction Roof covering: Concrete single lap interlocking tiles Roof insulation: 450mm mineral wool External walls: A+ rated cavity wall construction Facing brick: Walls and reveals Cavity insulation: 200mm full fill polystyrene bead Inner walls: Medium density aggregate block with wet plaster Windows: A rated UPVC and doors Lintels: Pre-stressed concrete inner leaf with outer steel C lintels First floor: B rated pre-stressed concrete beam and block, 75mm sand cement screed Ceiling to u/s of first floor: Metal framed ceiling laths with plasterboard and skim Ground floor: B rated, pre-stressed concrete beam and block, 90mm sand cement screed and 200mm polystyrene insulation Internal walls: Medium density concrete block with wet plaster finish Staircase: Timber softwood Heat source: Condensing gas boiler Heat distribution: Wet underfloor heating Renewables: 27m 2 of photovoltaic panels Ventilation: Mechanical ventilation with heat recovery system Foundations: Precast piles and precast ground beams The material selection was made by the RSL and its design/construct team, within the cost and buildability context. 10 The building fabric

11 The building fabric Ground floor Two types of beam and block construction were evaluated for the ground floor, one using polystyrene blocks and the other with concrete blocks. Both had a 90mm screed finish, containing underfloor heating pipes. For U-values down to 0.15 W/m 2 K, the polystyrene option requires no additional insulation. However, to achieve the very low design value of 0.12 W/m 2 K, approximately 50mm of extra insulation is necessary. The concrete block option requires 200mm of insulation, resulting in an overall floor depth that is around 150mm greater than that required with polystyrene blocks. Other factors taken into consideration centred on cost and the environmental rating for which the polystyrene option scores an A+ rating in the Green Guide. However, it was decided to go with the concrete block option as the potential exists to upgrade this from a B to an A rating by specifying screed with a high recycled content, and also because the overall floor depth was not considered to be a particular design issue. The design U-value of 0.15 W/m 2 K was achieved using a 200mm cavity fully filled with polystyrene beads and medium density aggregate block for the inner leaf. The choice of medium density blocks over other options was marginal, but was driven by a combination of cost and the added benefit of their reasonably high mass. However, had wall thickness and lower thermal conductivity been more of a driver, the greater insulating properties of aircrete blocks would have reduced the depth by around 10mm, or 15mm when using a thin-joint system, which would also be likely to reduce build time. With the chosen combination of medium density aggregate blocks and polystyrene beads, the wall has an overall thickness of around 415mm, including finishes. The design team also considered using mineral wool quilt, blown fibre and phenolic foam board with a 50mm cavity, which would have reduced the overall wall thickness to around 385mm; however with low build cost as a key requirement, the benefit of this option was judged to be of less importance than the comparatively lower price of polystyrene insulation. It also enabled the optimum cavity width to be specified as this was not determined by standard manufactured insulation thicknesses. Roof The design of the roof structure required a minimum pitch, defined by the need to achieve optimum performance in terms of weathering, whole life costs and the use of solar panels to achieve code level 5 performance targets. Consideration was given to the selection of either timber cut roofing members or trussed roofing. A timber trussed roof was specified as it represents best value and is readily available. A safe access zone formed part of the design, allowing proper accesses to the mechanical ventilation plant. Mineral wool, polyurethane board and natural wool were all considered for the cold roof structure. The final choice was 450mm of mineral wool, which was found to be the most economical way of achieving the required U-value of 0.12 W/m 2 K. A traditional roof covering was a fundamental design requirement in order to meet the aspirations of the RSL for a traditional design acceptable to planning authorities on a national basis. The roof covering has to be compatible with solar panels. Double lap and single lap interlocking concrete tiles were considered, with the single lap option selected for being the most cost-effective. External walls A primary objective of the external walls is to meet the NHBC requirements, BBA certification, and RSL requirements for cost-efficient, mainstream construction methods and materials. The result was a cavity wall, with a choice between facing bricks for the outer leaf or concrete blocks with a rendered finish, to suit whatever the local architectural style might require. Thermal performance targets achieved. 11

12 Achieving Code Level Five with Concrete and Masonry Windows Timber and UPVC windows were evaluated for thermal performance, maintenance requirements, ease of cleaning and durability. Despite lower levels of embodied CO 2, timber was ultimately ruled out due to higher maintenance requirements; an issue of particular importance to the RSL. This left UPVC windows as the preferred option and they were ultimately selected. In addition to the maintenance issue, the decision was also influenced by cost and the recent improvement in the Green Guide environmental rating for UPVC windows, which has moved from C to A, reflecting the material s good whole life performance i.e. low maintenance requirement and ability to be recycled at end of life. The design U-value was initially estimated to be around W/m 2 K, reflecting the typical performance of energy efficient windows from UK suppliers. However, this was revised down to 0.8 W/m 2 K when it was found that a mainstream supplier can provide this level of performance in its UK manufactured UPVC windows by incorporating triple glazing with krypton gas and low emissivity glass. Internal walls Concrete blocks, timber studs and steel studwork were all considered for the internal walls, but as a wet plaster finish was the preferred option for the external walls, it made sense to extend this to all of the walls. Consequently it was decided to use medium density aggregate blocks on the ground and first floor, which in turn brought the added benefit of a tough finish, greater mass and good resilience to damage in areas at risk from flooding. First floor Both timber and concrete solutions were considered, however the benefits of thermal mass and better acoustic and fire separation led to a choice of concrete. A pre-stressed concrete wide span floor and pre-stressed concrete beam and block floor were both considered by the design team, with little to choose between them. But as the design assessment was for a single dwelling it was assumed that there would not be a crane on-site, which in turn favoured the beam and block option. For volume build the choice may be different. Lintels The design constraint of a 200mm cavity with load bearing masonry required the consideration of readily available solutions using separate lintels for each wall leaf. The design team considered steel C lintels, precast stone, and reinforced concrete inner lintels before selecting reinforced concrete inner lintels with an outer steel C lintel. Thermal bridging Non-repeating cold bridging at junctions, lintels etc. is minimised through the use of high performance construction details with an overall y-value of 0.04 W/m 2 K which, in a modern semi-detached house, can reduce CO 2 emissions by around 7 per cent compared with standard Part L performance. Low conductivity basalt fibre ties, with a thermal conductivity around 20 times less than stainless steel, are specified for the cavity walls. For the cavity closers, extruded PVC with a rigid urethane insulated core was chosen. At least one manufacturer can provide these closers with jointing clips to allow the smaller, more commonly used sizes of mm to be extended for cavities up to 200mm (as used in this project). Staircase The design team considered a precast concrete stair solution; however, on balance, for this single development a timber stair was seen as a cost-effective and readily available solution. For volume build, where there is more likely to be a crane on-site, the concrete option would become a more realistic choice. Air tightness The design air leakage rate was set at 2 m 3 /(h.m 2 ). Whilst challenging, this is a realistic target, as demonstrated by the recent Stamford Brook development of around 700 highly insulated masonry homes. A key lesson from Stamford Brook was that a masonry house can achieve an air leakage rate of 2 m 3 /(h.m 2 ) provided that care is taken with detailing and sequencing of trades on site. The choice of primary air barrier was made early in the design process. A rough sand and cement parging coat on the blockwork inner leaf would have provided an effective solution; however this approach is generally used in conjunction with a plasterboard finish, which the design team wanted to avoid for reasons already described. Consequently, the chosen solution was wet plaster, which seals the blockwork in the same manner as parging but with the advantage of being able to conduct more heat to and from the wall than is possible with plasterboard on dabs (see surface finish section on page 9). Other points in its favour are its resilience to flood damage and general robustness which is a requirement of social housing programmes. Points against a wet plaster finish are the time and skill needed to apply it, although modern projection plastering techniques can significantly speed up the process. Drying time can also be seen as a disadvantage. 12 Building fabric and services

13 Building services Heat source/hot water The main design requirements influencing the choice of heat source centred on the following issues: ease of maintenance cost use of a known technology code score compatibility with other aspects of the design. A small wood chip biomass boiler was initially considered as this represents the type of technology that would ideally be used as part of a much larger district heating scheme serving a whole social housing development. This pointed the way to a wet heating system which could be supplied with hot water from a range of sources (either on-site or nearby), helping future proof the heating design. However, the use of a small wood chip boiler was subsequently ruled out on the grounds of practicality for a single house. A ground source heat pump was discounted on the grounds of cost and because, like all heat pumps, it does not attract any code credits under the Pollution category. In contrast, credits can be scored for the low NOx emissions from a condensing boiler, which was the eventual choice since it is was also best able to match all the design requirements listed above. A class 5 boiler was specified with an overall efficiency greater than 90 per cent, attracting 2 credits for low NOx emissions. As condensing boilers provide relatively cheap hot water, it was not felt worthwhile to also install a solar hot water system, which would have added complexity, cost and been difficult to site on a roof with PV panels already occupying most of the south facing area of the roof. Photovoltaic (PV) technology Since a key requirement for the RSL was low maintenance and the use of proven technologies, it was decided that photovoltaic panels would be installed to meet the entire on-site renewable energy requirement. This decision was also driven by the need to reduce the overall complexity and maintenance requirements of any low/zero carbon technologies installed in the house, and limiting the design to a single technology makes it easier for the occupants to operate. Heat distribution Affordable housing design parameters are complex because of the need for designers to work within the wide range of mandatory compliance criteria, including Housing Quality Indicators. As a result, the furniture layouts and window/wall space have an impact on the limited positions for radiators. Options considered included underfloor heating and pressed steel radiators, from which it was decided that to fulfil requirements for even heat distribution and compatibility with the mass of the floors, an underfloor solution was the most effective option. The decision was also influenced by the very thermally efficient windows (0.8 W/m 2 K), which have minimal downdraughts, so have little need for radiators to counter them. This in turn frees up space and allows the furniture layout to be optimised. A further benefit of underfloor heating is the low flow and return temperature, which helps save gas by enabling the boiler to operate in condensing mode for much of the time. In terms of comfort, underfloor heating makes floor tiles a more practical option than would otherwise be the case, and their use also allows access to thermal mass in the screed. So, there is some synergy between underfloor heating, thermal mass and tiled floors, which also provide a durable surface. Mechanical ventilation Mechanical ventilation with heat recovery (MVHR) was specified since, without it, the low air leakage rate of 2m 3 /(h.m 2 ) is likely to result in poor air quality and the potential for condensation problems. The ability to recover waste heat in mechanical systems can also make a useful contribution to overall energy efficiency of dwellings and reduce CO 2 emissions. For example, the use of MVHR in a modern semi-detached house with an air leakage rate of 2m 3 /(h.m 2 ) can reduce emissions by around 6 per cent compared with natural ventilation alone. The MVHR system selected for the project is compliant with Appendix Q of SAP, and combines low fan power with a counter flow heat exchanger that recovers up to 91 per cent of the heat in the discharge air. During warm weather, a bypass system diverts the incoming air around the heat exchanger, preventing the warm discharge air from increasing the supply temperature. The unit takes and exhausts air through the roof. The three bedrooms, lounge and kitchen each have a fresh air supply, with extract points located in the kitchen, bathroom and ground floor WC. Figure 3: MVHR layout (blue = supply/ red = extract) The choice of underfloor heating increased space planning flexibility. 13

14 Achieving Code Level Five with Concrete and Masonry Summary and lessons learnt Figure 4: Summary of key design information House type Code level 5 Floor area 85m 2 Air tightness 2m 3 /(h.m 2 ) Heat loss parameter 0.81 Cold bridging y-value 0.04 Ground floor Walls Roof Windows Upper floor Internal walls Ventilation Heat source Heat distribution Three-bedroom, five-person, end or mid-terrace Beam and block, 0.12W/m 2 K Brick and block, 0.15 W/m 2 K Timber-trussed, concrete tiles, 0.12 W/m 2 K UPVC, triple glazed, 0.8 W/m 2 K Beam and block Block MVHR Class 5 condensing boiler Wet, underfloor Renewables Photovoltaic panels, 27m 2 Water consumption Home office Lifetime Homes Secured by Design Estimated code points 1. Energy 2. Water 3. Materials 4. Surface water run-off 5. Waste 6. Pollution 7. Health and well-being 8. Management 9. Land use and ecology 80l/p/day Yes Yes Yes out of out of out of out of out of out of out of out of out of 12 Lessons learnt It is important for specifiers to talk to their supply chain as manufacturers may have new products available that can help score credits within the Code. Talk to the technical and sales people to get different options. Evaluate the cost/benefit of different insulation materials to avoid overspecification. For example, with this project it was found that polystyrene bead insulation provided a good balance between cost and performance for the cavity walls. It also enabled the optimum cavity width to be specified as this was not determined by standard insulation thicknesses. Beware of agreeing to changes in the original product specification, as substitute materials and systems may not score the same credits in the post-construction assessment. A generic design can be produced up to a point, but window size and location should ideally take account of site specifics (orientation and overshadowing) so that daylighting and passive solar gain can be optimised. This can influence the credits scored, as can other site specific details such as flood risk and ecological value. Talk to your code assessor early in the design process, and if possible include them in the project team. Their involvement at the outset will assist in maximising the points scored and help avoid missed opportunities. Total estimated code points out of Summary and lessons learnt

15 Summary This design exercise utilised the expertise of an RSL client, design team, contractor/housebuilder and was based on a developed standard house type. It shows that concrete and masonry construction can produce cost-effective, locally and responsibly sourced solutions to the higher levels of the Code for Sustainable Homes. This can all be achieved, whilst at the same time addressing the needs of the public sector for long-term, durable and flexible construction solutions. References: 1. Housing Quality Indicators, version 4, April Design and Quality Standards, Housing Corporation, April The Lifetime Homes Standards, Lifetime Homes Durability, long-life and future adaptability are all integral to the solution. 15

16 The Concrete Centre Riverside House, 4 Meadows Business Park, Station Approach, Blackwater, Camberley, Surrey GU17 9AB Ref: TCC/04/09 ISBN: First published 2009 MPA - The Concrete Centre, 2009 The Concrete Centre is part of the Mineral Products Association, the trade association for the aggregates, asphalt, cement, concrete, lime, mortar and silica sand industries. All advice or information from MPA -The Concrete Centre is intended only for use in the UK by those who will evaluate the significance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted by Mineral Products Association or its subcontractors, suppliers or advisors. Readers should note that the publications from MPA - The Concrete Centre are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.