“There was strong support from respondents to most of the recommendations [proposed as changes to The Code], with over half the questions receiving more than 70 per cent support [and only five questions receiving less than 50 per cent support]” (Department for Communities and Local Government, 2010c).
This shows that there is a high level of support for the proposed changes to The Code, and that these changes will positively benefit the comprehension, accessibility and implementation of The Code.
The package of changes is expected to deliver a reduction of construction costs compared to a reference case (Department for Communities and Local Government, 2010b). This will allow a more cost effective implementation of the code, increasing the attraction of building to in accordance with The Code. For example changes to the surface water run-off requirements of Code homes, where management of surface water by infiltration is not possible due to ground conditions, is expected to deliver a large cost saving, amounting to £112m across all housing (£56m in the publicly-funded sector) (Department for Communities and Local Government, 2010b, p.45).
Department for Communities and Local Government. (2010b). Also stated in the 2010 proposal for changes in The Code is the suggestion that mandatory CO2 reduction requirements of Code level 5 and 6 remain unchanged due to the ongoing work on the definition of the zero carbon policy and the minimum carbon compliance level. However, this is expected to be reviewed again in a later review of Code policy.
This seems like it could be a major stumbling block of the widespread implementation of The Code, and completion of the zero-carbon definition should be of highest priority to ensure that no uncertainty will be filtered through, possibly causing either mistakes in comprehension and/or lack of confidence in its cohesion.
Further assessment of other issues are also stated in the final impact assessment of the revisions, and include detailed consideration of the introduction of an Energy Display Devices issue. Increasing the uptake of energy display devices is intended to “drive reduction in energy consumption by providing better information to occupants on their usage.” (Department for Communities and Local Government, 2010b).
This is an excellent revision to The Code, as it also augments the government Smart Metering Implementation Programme (OfGem, 2010). Smart meters enable people to better understand their energy use, and have been gaining in popularity as a technology that can both help homeowners reduce energy consumption and enhance customer service (Hoiland, 2010). They are also necessary when using PV cells and other micro generation equipment to allow calculation of how much energy is being generated, and if in sufficient quantities how much is being sold back to the grid.
Breakdown of Categories, Issues, Credits and Weightings
Overview
The code sets out 9 categories of environmental impact, which are sub-divided into a number of discrete issues. The number of issues per category varies, as do the amount of credits available to be gained within each category. A weighting factor is also applied to each category , meaning that the actual value of each credit in in each category differs. For example, a Water category credit is worth more than a Materials category credit, although more credits may be gained within the Materials section.
Although it is logical that some areas deserve a heavier weighting, this does not seem the simplest method of calculating the environmental performance of a building. Possibly a system of allocating credits based on the category’s would allow removal of the weighting factor for a simplified and easier to understand system.
The use of optional credits to score the overall sustainability provides flexibility for the design of the house, allowing compromise. This is important if the code is to achieve widespread success, as some buildings will be limited by constraints and therefore will not be able to meet certain targets fully. For example in a dense complex of flats it may not be viable to provide individual home composting facilities, but 2 points may be regained by providing adequately sized, secure and convenient cycle storage.
However to ensure that each house does reach minimum standards for each level, mandatory requirements are set which must be met. For levels 4 and 5 a minimum improvement of co2 emissions is required, and for level 6 a net zero co2 emission is required (passive).
This ensures that each level of housing has a minimum level of sustainability in the key areas, ensuring that weak points and loopholes are avoided.
Energy and CO2 Emissions
This is the most important category, contributing 36.4% with 31 credits available. A total of 9 issues are listed (ENE 1-9) and cover a wide area of Energy and CO2 conservation, even allowing 2 optional credits for adequate and secure cycle storage, “thus reducing the need for short car journeys and the associated CO2 emissions” (Department for Communities and Local Government, 2010a).
This shows that thought has been given in respect to how people live around buildings rather than just within them. The lack of security and amount of crime associated with external bike racks is often a disincentive to owning and maintaining bicycles.
A major change in the 2010 revision of the Code for Sustainable Homes is the rebalancing of ENE 1 and ENE 2. The 2007 edition awarded 15 credits for CO2 reduction in ENE 1 and 2 credits for the heat loss parameter in ENE 2. The 2010 revision awards 10 credits for ENE 1 and has changed ENE 2 to ‘Fabric Energy Efficiency’, allowing 9 credits to be awarded. This allows a greater amount of credits to be gained by “improving fabric energy efficiency performance thus future-proofing reductions in CO2 for the life of the dwelling” (Department for Communities and Local Government, 2010a, p.40).
The assessment criteria has also changed from a basis on a Heat Loss Parameter to the Fabric Energy Efficiency, allowing a more detailed assessment of the building fabric, but resulting in a higher complexity of calculation.
Water
The efficient use of water only has 6 points, but due to its relative importance is has the highest weighting factor (9.0%), giving an approximate credit value of 1.5. The assessment criteria is solely based on the calculation of litres per person per day used, giving mandatory levels for the achievement of certain levels.
The category does not give consideration to the source of water, for example rainwater harvesting.
To more accurately calculate the sustainability of the water usage of a building, consideration should be given to water source. For example, grey water may be used for the flushing of toilets, and harvested rainwater may be used a primary water source if sufficiently filtrated (for example utilising reverse osmosis and UV systems).
A main drawback of water efficiency can often be the installation of ultra efficient showers with very low flow rates. It is of the authors opinion and other persons discussed that a low flow shower would lead to dissatisfaction in flow level, and would either act as a disincentive to water efficiency, or would lead to the person taking longer average times in the shower, negating the proposed increase in efficiency.
Materials
The materials used in the construction of the building has many areas to gain credits but has a low weighting, giving only 7.2% of the total influence of sustainability.
The author considers this to be a very low figure, being considered not as important as Water, Health + Wellbeing, Management or Ecology. Considering the large amount embodied energy that must be used to create various building materials, it is of the authors opinion that this weighting is possibly too low.
15 credits may be awarded for the environmental impact of materials, and are calculated by using the Green Guide Calculator tool.
Additionally, 6 credits may be gained in the specification of responsibly sourced materials for the basic building elements, and 3 for finishing elements.
Surface Water Run-off
Surface water run-off increases can ingress pollution into the watercourses and increase the risk of flooding. The development of a building can also increase the ‘man made impermeable area’ (for example a tarmac driveway where water cannot soak through).
1 point is awarded for ensuring no discharge for rainfall depths of 5mm, with an additional point awarded if the run-off from surface receives an appropriate level of treatment in accordance with The SuDS Manual to minimise the risk of pollution.
2 points are available for situating the development in Zone 1 defined in PPS25 and where the Flood Risk Assessment indicates there is low risk of flooding for all areas.
This category is only given a weighting factor of 2.2%, making it the least significant. This could be challenged by the continuing threat of flooding and the expansion of building on flood plains, especially in the south-east of England which is sinking due to the isostatic recovery of Scandinavia and Scotland.
Waste
WAS 1 focuses on providing adequate internal and external storage space for recyclable and non-recyclable household waste, and is an important consideration as it will both encourage people to recycle and provide an appropriate storage area for both types, helping to ensure waste does not litter outside streets.
Brighton terraced student houses have a particular problem in regard to this. A lack of dedicated storage areas sometimes leads people to just ‘chuck it all away’ and with no suitable storage areas rubbish sacks are often torn apart by seagulls, littering the streets.
WAS 2 is concerned with the promotion of “resource efficiency via the effective and appropriate management of construction site waste.” (Department for Communities and Local Government, 2010a, p.162)
Construction site waste is an important issue regarding the life cycle of a building. Other than scrap value and the avoidance of tipping charges there is little incentive to responsibly manage construction site waste. WAS 2 allows credits to be awarded by employing a Site Waste Management Plan (SWMP) and diverting a percentage of waste from landfill.
The 2010 revision of WAS 2 has increased the points available by 1, but has removed the mandatory element to all levels.
Due to the small weighting of these 3 points (0.80) there could be a risk that this very important issue could be overlooked as merely ‘optional bonus points’. A possible improvement would be to have mandatory percentages of waste diverted to landfill allocated to each level.
Pollution
The aim of the Pollution Category Issue POL 1 is “to promote the reduction of emissions of gases with high Global Warming Potential (GWP) associated with the manufacture, installation, use and disposal of foamed thermal and acoustic insulating materials” (Department for Communities and Local Government, 2010a). This credit is only issued if the GWP is under 5, referring to both the blowing agent and the material.
POL 2 is concerned with the reduction of nitrogen oxide into the atmosphere and depends on the boiler class to BS EN 297: 1994. 3 non mandatory credits are available in this category. If no NOx emitting system is present, the 3 full points are awarded.
This category is only given a weighting of 2.8%, and is therefore does not have much relative importance
Health and Well-being
The health and wellbeing category is concerned with the provision of daylighting, sound insulation, private space and lifetime homes. Although these factors do not directly affect the sustainability of the building consumption (apart from daylighting which can reduce lighting energy) they are concerned with homes being a pleasant and adaptable place to live, thereby increasing quality of life and ensuring that poorly design houses are not created that may need to be demolished and rebuilt if considered obsolete.
This category has a weighting of 14%, making it the second most significant category. This signifies that the government considers quality of life and the satisfaction of buildings an important issue, and creates the challenge of creating energy efficient, sustainable buildings that are still well suited for modern and future living.
Management
Management promotes the:
- guidance of occupants to operate the building efficiently
- construction the building in a responsible manner
- mitigation of the environmental impact of the construction
- design of safe and secure developments.
This category has a 10% weighting and is completely optional, creating the same challenge of meeting sustainability targets whilst not infringing on building design and use.
MAN 1 should be of particular importance, as a building’s energy efficiency rating building may always will be negated by improper usage. This could also become an excellent tool to market ‘green’ houses, as occupants will be able to save money on fuel bills. It is of the author’s opinion that this issue become mandatory for all levels.
Ecology
The Ecology Category is concerned with protecting and enhancing the ecological value and features of the site, whilst ensuring the efficient use of the bulding’s footprint.
This category has a 12% weighting and is optional, allowing ‘bonus’ credits to be awarded to achieve a higher rating level.
Problems with the Code for Sustainable Homes
Technical problems in the calculation of credits for the code have been identified by the Good Homes Allowance (16). These include issues such as:
- It is easier to achieve CSH levels 3 and 4 by using electric on-peak heating, than by the more carbon efficient option of gas heating
- It is easier to achieve Building Regulations and CSH levels 1-4 if the building is bigger, and the building form is less efficient.
However the GHA has stated it is not seeking to undermine the credibility of The Code, rather help ensure that the Code is upheld as a useful and trusted mechanism for achieving carbon reduction in new housing. Therefore, the process of identifying errors so that they may be eliminated in further revision is an important process to ‘iron out’ problems.
Also, it may be possible to include certain features (e.g. bike storage, bird table) in areas where they would not be reasonably practicable, just to gain a higher rating. However, this could be seen as an unfortunate inevitability caused by persons looking to exploit the system rather than embrace it, and not an actual problem per se.
The author would strongly advocate the increased use of compulsory issues to gain higher ratings, particularly MAN1 which would be unaffected by potential building constraints.
Conclusion
The Code for Sustainable Homes is an excellent policy and guidance tool for helping people to increase the overall sustainability of domestic structures. Although there are some flaws that prevent it from being considered perfect, it is an important structure that will lead the way in providing the UK with more sustainable homes.
It will be interesting to see what revisions are made to the Code, if any more potential problems arise and if the code will fulfill all of its potential benefits, for example becoming a marketing tool to promote sustainable housing as a desirable characteristic.
Critical appraisal of new house for energy and CO2 emissions
Name: The Saltings
Location: Suffolk
Architect: Haward Architects
System Developer:
Beattie Passive Build Systems Ltd
Completion: Spring 2011
CO2 Emissions:
85% reduction over Part L 2006
Description
The Saltings is a large (300m2) 4 bedroom prestige home which is being built to a very high fabric performance standard. It uses a site assembled timber frame construction system with insulation injected into the wall floor and roof cavities: an approach that speeds up construction, reduces the risk of thermal bridging and achieves high airtightness performance. This construction method (Beattie Passive Build System) has LABC registered systems approval.
Structural construction is of a concrete beam on pad foundation, with a site-assembled timber frame
With its solar thermal and solar photovoltaics the design meets level 4 (Energy) of the Code for Sustainable Homes and could be upgraded to level 5 or 6 with the addition of more PV.
Approach for achieving low carbon status
Fabric Walls, floors and roof are built with 360mm of insulation (300mm in the structure and 60mm additional overclad insulation). The house also has triple-glazed windows.
Heat and power A mechanical ventilation heat recovery system recycles heat from exhaust air. Solar technologies provide water heating and electrical power.
Thermal Comfort The thermal mass of components and phase change materials together reduce extremes of temperature. The large south-facing doors have heat reflective window blinds to reduce solar gain. Passive ventilation (with a thermostatically controlled stairwell rooflight) provides summer cooling.
Outline energy strategy
A very high performance fabric coupled with solar technologies, MHVR and careful design to minimise solar gain.
Envelope
Walls: U = 0.11 W/m2K
300mm continuous EPS insulation, overclad with 60mm phenolic insulation.
Roof: U = 0.11 W/m2K
400mm continuous EPS insulation.
Floor: U = 0.11 W/m2K
300mm continuous EPS insulation, overclad with 25mm phenolic insulation.
Windows: U = 0.9 W/m2K
Triple glazed with low e glass.
Airtightness: 1.0m3/m2/hr at 50 pa
As well as the continuous insulation, the design has a continuous vapour check layer and on site, a methodical taping and joint sealing regime.
Heat and Power
Space heating
In-line heater and wood burner in lounge.
Mechanical Ventilation Heat Recovery
Greenwood MVHR system provides fresh clean air and recovers heat from out-going air.
Solar Thermal Array: 3.4m2
Provides hot water. Immersion heater in tank boosts temperature as required.
Photovoltaic Array: 2.7kWp
Electric power provided by roof mounted photovoltaic panels.
Phase Change Materials (PCM)
PCM in clay boards fitted to ceilings: this stores any excess heat (e.g. solar gain) and releases it when the building cools down.
Alignment with the Code for Sustainable Homes (Design Stage)
Fabric Performance Target Comparison
Evaluation and Discussion of Energy Issues
The building has been assessed using the 2007 version of the Code for Sustainable Homes. This allows a maximum of 29 credits to be awarded for the Energy and Carbon Dioxide Emission Category, of which the building scored 26.
For the energy issue category ENE 1, the building was awarded 12 credits out of a possible 15, giving a score of level 4. This is due to an 85% reduction in carbon emissions which can be attributed to the specification of :
- Solar thermal arrays (providing hot water)
- Photovoltaic arrays (providing electricity
- MHVR System (recovering heat from exhausted air)
- Phase Change Materials (storing and releasing excess heat)
The solar thermal and photovoltaic arrays are able to supply the building with much of the required hot water and electricity. The in-line heater provides space heating, augmented by the MHVR system, PCM materials and very high U value of the building envelope to increase efficiency.
If the ENE 1 rating was to be improved, simply adding additional PV arrays to increase the available zero-carbon energy source would be needed. This would allow less reliance on additional grid electricity to power the in-line space heater, water immersion heater and electrical appliances.
All the optional energy issue categories (ENE 2 – ENE 9) have been met.
Therefore, this building could easily be upgraded to level 5 or 6 in the Energy and Carbon Dioxide Emission Category.
Another key issue of this building is the of this building is the high level thermal performance of the fabric building envelope. All areas (apart from the doors for which information was not available) exceed the 2016 requirement.
The usage of phenolic insulation reduces the risk of cold bridging and has several design advantages, such as very low U value (0.018W/m2K) and increased construction speed.
Phenolic insulation also has a very low embodied energy content, is available in both CFC and HCFC free forms and can make a significant contribution to attain credits for Materials Category Issue MAT 1. (Good Homes Alliance, 2010, p. 2). Other benefits include ‘exceptional’ fire performance, with up 2 hours fire resistance, high structural strength and low water vapour permeance.
The building utilizes triple glazing which has excellent thermal performance, but triple glazing is more costly to produce, produces much heavier sections and has an embodied energy approximately 50% higher than double glazing (Brinkley, 2008).
Consideration should also be given if the building was assessed under the 2010 revised Code. The 2010 revision allocates 9 credits for the consideration of the Fabric Energy Efficiency Issue, assessed by calculating the kWh/m2/year.
Although the exact calculation of this figure cannot be completed due to insufficient information and being beyond scope, it would be expected that the building would score a high level due to the very high thermal performance of the building fabric.
Conclusion
This building is an excellent example of the results that may be achieved by following the Energy and CO2 Emission Category in the Code for Sustainable Homes. In all possible areas the building has excelled to produce a very well insulated, sustainable home with high reliance on renewable technologies which can be quickly and easily constructed. The building fabric meets and surpasses the projected Part L 2016 requirements with the use of materials that have added benefits besides thermal insulation. The low and zero carbon technologies are easily expandable to reduce the dependence on electricity from the electrical grid, and to achieve Level 5 or 6. There is some uncertainty to why this project was not just completed to Level 6 from the onset.
Areas of possible further study would include the cost effectiveness of this high quality approach and its potential market price and profitability. It is normally seen that a building with exceptional performance in area normally comes with a price attached. The buildings performance in the other 8 categories of the Code for Sustainable Homes, and its performance against the revised 2010 version of the Code would also prove interesting areas of further study.
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