Achieving Zero Carbon

In the UK the housebuilders at large scale constructions are responsible for the majority of new homes in the UK and whohave shown that they are aware of the proportion of CO coming from the housing stock and nearly all have the reduction of CO as one of their key business objective and have shown commitment to tackling the issues of climate change in the UK. However as housebuilders are committed to reducing carbon emissions there is also a concern at the considerable challenge which faces them in meeting the government's ambitious sustainability targets and actually delivering to the homeowner an affordable and appealing home to live.

The housebuilders and developers are the main bodies responsible for delivering zero carbon homes to us, but it is the government who are the main instigators for setting guidelines and sustainability targets in the UK for it to become a zero carbon and emission free country. The main target in which the government put in place was legislation in which will aim to cut the UK's emissions by 34% by 2020 and by an 80% reduction in the greenhouse gas emissions by the year 2050 and also the policy to which all new homes should be zero carbon from the year 2016. In reaching this goal the government has set out improvements to energy requirements in the building regulations in the years 2010, 2013 with the final leap in 2016, reaching zero carbon. The actions in which the government are taken to ensure that these targets are been met would include:

  • In 2009 they set up a community Energy Saving Programme, this starts trailing the "whole house" treatments in low income areas.
  • In 2010 there will be about 95% of the social housing stock in England meeting the improved decent homes standard. A scheme also will be introduced called "clean energy cash-back scheme" which will pay out if there is a use of low carbon sources to generate electricity. Within 2010 there will also be a change in the building regulations to improve the energy efficiency by 25% compared to the 2006 regulations.
  • By 2011 Six millions homes will be insulated under the Carbon Emissions Reduction Target, Decent Home, the Community Energy Saving Programme and Warm Front. The energy cash back scheme which was introduced in 2010 is put in place of April of this year for use of low carbon sources in the generation of heat. The traditional light bulb will no longer be sold after this year also.
  • The building regulations will have improved energy efficiency by 44% in 2013 compared to the 2006 building regulations.
  • In 2016 all new homes should have achieved and reached the target of zero carbon.
  • From the government taken the actions of delivering energy savings, helping people meet the costs of a the transformation, raising the standards and also helping communities by 2020, will add on average an additional 6% to today's household bills.

One of the major actions the government has taken and is a major incentive in reaching the goal of 2016 was the introduction of stamp duty land tax relief for new zero-carbon homes. This relief is designed to incentivise the demand for zero-carbon homes among homebuyers and encourage microgeneration technologies and also provide developers with a marketing tool to sell zero-carbon home while also reducing potential cost barriers for developers given such homes cost more to build then conventional homes

The government introduced "The Code for Sustainable Homes" which is the standard by which new homes are being judged for their green credentials. The code covers range of environmental issues such as energy and carbon dioxide emissions, water usage, run-off water, pollution, site management e.t.c. Homes are assessed at the design stage of the construction, with each building having its own assessment and awarded a certificated ranging from level 1 to level 6 all depending on its performance. To achieve any level there is a challenge in doing so, as there are mandatory issues in which have to be closely addressed, to reach the highest level (level 6) significant changes would have to be applied to the conventional way of construction. Builders would prefer the requirements of the code for sustainable homes to be built into the building regulations to be introduced at the same time and enforced by building control rather than the planning departments.

Potential Pitfalls with the code-

As I suppose with most things there will be pitfalls in which will follow, and while improving the sustainability of a development there also could be negative impacts in other areas if care is not taken, which consist of:

  • There will be additional build capital cost, which is probably quite obvious, but there are also hidden costs such as installation and also fluctuating prices due to rising demand in a market with limited supply.
  • Housebuilders believe that the additional cost will need to be financed by reductions in land values, which raises concerns that landowners will not be willing to sell land at significantly lower prices. This could lead to shortages in land supply, fewer homes being built and heightened affordability problems.
  • Measures that need extra space such as the use of soakaways, passive solar design, biomass heating systems, or Lifetime Homes, can have significant impacts on the site layout, and need all to be considered at the early stage of design.

Thermal Efficiency of the building:

In the construction of a new build the housebuilder should pay particular attention to the insulation as it will serve to reduce the heating cost of the building or in different climates reduce air conditioning costs. Other considerations for the housebuilder consists of: Prevent moisture build-up within the envelope by placing vapour barrier on the warm side of the wall, weatherstrip all doors and place sealing gaskets and latches on all windows to prevent air leakage to avoid convective loss and unwanted infiltration, specify construction materials and details that reduce heat transfer, consider earth berms to reduce heat transmission and radiant heat loads, the use of sod roofs and buried exterior walls provide thermal mass that will absorb and control solar gains (Points taken from guest lecture with Architect x on 8th Oct 09). The materials used in the external/main building envelope are vital, as they play a major role in the thermal efficiency of a new home. For the external envelope the main four systems/technologies in which housebuilders use are:

  • Traditional Brick + Block.
  • Panel System Masonry.
  • Timber Construction.
  • Lightweight Panel System.

Traditional Brick + Block:

The brick/block construction which is made up of the insulated cavity, an outer leaf of block work and also an inner leaf of block work, it is the most popular type of external envelope used among housebuilders. The inherent thermal mass regulates temperatures inside the structure more efficiently than lightweight materials. The disadvantage is that it can be difficult to achieve the high levels of air tightness required using conventional techniques in the challenging environment of a traditional building site. Housebuilders are weighing away from using the conventional brick and block methods of construction as there are improvements to standards, and builders believe such improvements can be achieved without additional cost through new techniques and materials, e.g. using off-site or modern methods of construction using concrete panels.

Panel System Masonry:

The Panel System Masonry looks a lot like the traditional brick and block construction and also uses a lot of the similar materials. The advantage of using this type of system for the housebuilder is that it is manufactured off-site in a factory environment with the disadvantage been the transportation of the panels to the site, the cost of the transport in both monetary and in CO terms be higher than in the lightweight system. The overall mass of this structure will provide good thermal mass to keep in the heat in the winter and also slow down the unwanted absorption of excess heat in the summer.

Timber Construction:

In the construction of timber homes the housebuilder uses sustainable materials and the cost of transport are lower due to the lower mass. This type of construction can be highly effective at retaining heat if it is highly insulated with the cost of the build for the housebuilder been relatively inexpensive due to the speed of assembly. When using timber fame construction reaching code 1-3 can be achieved quite easily, Code level 4-6 can be produced but requires significant changes to current methods ofdesign and construction. But it is very much possible as the first code 6 home was built using a timber frame construction.

Lightweight Panel Systems:

Lightweight Panel Systems are very familiar to timber frame construction where the systems uses a lot of lightweight structures manufactured off-site and also using sustainable materials. For these reasons the lightweight panel system scores high on the code criteria. The panels fit together in modular fashion, forming the building envelope and carrying the structural loads. The lightweight panel system is less familiar to the housebuilder than timber framed homes and perhaps less adaptable due to the often complex combinations of materials and membranes used in the panels.

Water Recycling/Conservation-

For housebuilders today reaching the achieved goal of code 6 by 2016 the process's of recycling water and minimising water usage should be incorporated into the design and construction process of new homes so that housing can be energy and water efficient, saving homeowners money as well as reducing their carbon footprint. In efforts to minimise water use, grey water recycling and rainwater recycling will in practice be necessary, but builders are expressing concerns that the grey water and rainwater systems could also pose serious risk to human health. As most housebuilders are aware that the code for sustainable home covers the water use, most are underestimating that the daily use in a UK household per person is 150 litres. But there is still the question whether or not the homeowner will accept a different lifestyle to meet the water use targets.

Grey water Recycling:

The grey water recycling system's main advantage in which it has over the rainwater recycling system is that its water is more consistently available for use, as it does not depend on the amount of rainfall. This system collects the water used in showers, baths and hand basins and reuses the water for WC's.

Rainwater Recycling:

In the rainwater recycling system it collects rainwater run-off and stores it, it is normally stored in underground tanks on the same site. The water goes through filtration and the water can be used to flush WCs and also washing machines. This type of system is simpler than the grey water but there is a need for occasional maintenance.

Housebuilders are tending to favour schemes for the use of the grey water recycling and rainwater harvesting systems in achieving the goal for becoming zero carbon, as along with microgeneration there are concerns regarding the added service and maintenance responsibilities homeowners will face and also the availability of space to locate the hardware.

Microgeneration Technology-

Microgeneration is defined as the production of heat and/or electricity on a small scale from a low carbon source. For the housebuilder in relation to zero carbon homes, microgeneration means a source of heat or power that is not drawn from a national grid and is low carbon using renewable energy sources such as solar energy, wind, biomass or also thermal mass. For the housebuilder to accommodate microgeneration technology into the new homes they are considering three different approaches- Individual properties, at a community level and for also offsite schemes which would be wired directly into a local distribution system. Builders are looking at using the community and offsite schemes as the property level scheme raises concerns over the plot sizes required to meet the planning constraints are large enough to accommodate the infrastructure and whether the individuals will maintain them. From Fig 2.1 the technologies in which are going to be most likely to be employed are the solar thermal in which heats the water, photovoltaic which generates electricity, ground source and air source heat pumps for space and water heating.

Questions were asked to housebuilders, asking them do they have any confidence in the ability of microgeneration technology been delivered to the required levels for to meet the code level of 6 in zero carbon homes by the year 2016.

The results in which came back noted that only a quarter of housebuilders expressed any degree of confidence in the technology been delivered in time.

Main concerns regarding the introduction of the microgeneration technologies from a housebuilder prospective relate to the cost of the technology along with the reliability, servicing, maintenance and also the availability of the technology. Given that there is questions over the cost and reliability of the technologies it is also understandable why housebuilders are worried for the homeowners in which they will be able to understand and use the technologies and how long will the technologies actually last. For example, photovoltaic cells for roofs, if the life span of them is 15years, and you buy a house in which is 7years old and there is 30,000 pounds worth PV cells on the roof, would it be a good idea to buy the house or not?? The PV cells will save 300 pound a month but they will also cost 30,000 pound to replace all the PV cells when the time comes around.

As the Housebuilders have the approach in tackling the zero carbon objectives, there is a reluctance to build to the specified level as their is the issue that customers will not pay the premium involved, and also the homeowners may not accept the required new technologies which would undermine the zero carbon objectives. Most Housebuilders are aware of the carbon emissions and recognise the need to reduce emissions from all new homes but as they are responding to the governments targets, key concerns in which they have with the governments priorities is that they appear to focus almost exclusively on the 160,000 new homes that are built every year rather than the 21 million homes that are already built in the UK.

The Building Regulations:

For the housebuilder the building regulations set a baseline mandatory standards, for dealing with zero carbon homes they set an overall energy/carbon target for the dwelling, while allowing flexibility in how the standard in met. The energy carbon target which is known as a SAP rating can be met by improving the fabric of the building through better insulation and sealing of the fabric, draught-proofing of windows and doors e.t.c. The Building Regulations have improved the energy/carbon performance already. The energy efficiency standards for new homes are 40% better than those before 2002 and also 70% better than in 1990. Housebuilders are prepared to deliver high environment standards and customers are recognising the fact that the way homes are been constructed is changing. The building regulations alongside the Code for Sustainable Homes will provide for the housebuilder a framework to deliver high environmental standards for the customer. Improvements will be made to the energy performance of the building regulations so that all homes will meet the energy/carbon standards.

It was brought out earlier this year potential changes that might be brought into Part L of the building regulations. The main point been empathising that carbon emission level permitted for new building will be cut by 25%. The cut in carbon emissions is only one of the proposed changes to Part L in which deals with the conservation of fuel and also power. Other changes in which are been proposed to change include:

  • The introduction of a fuel-based target emission rate. The government plans to introduce this fuel-based target emission rate to deal as a problem with Part L is that it focuses on the emissions rather than the energy efficiency.
  • As from the diagram above there is a net zero carbon target (code 6) set by 2016, which was set by the code for sustainable homes, the amendments are geared towards ensuring that this target is met. There will be changes to the way the energy efficiency of homes are calculated, which will consist of the standard assessment procedure (SAP) moving form an annual energy calculation to a monthly calculation, to improve the accuracy of the figure.
  • There is the introduction of measures to ensure there is a compliance with Part L. This measure will call for all design-stage submissions to be accompanied by a copy of the design specification. Designers will also have to submit a commissioning plan at the start of the project to insure that the systems perform as intended. The government also want designers to use compliance software to list the key features that enable a building to meet its energy performance targets.
  • The requirement for pumps, lighting and low and zero-carbon technologies will be included along the change for new buildings to limit heat gains. This is an aim to avoid excessive solar gain for both air-conditioned and naturally ventilated buildings to prevent overheating in the summer.


How will existing homes become zero carbon??

A main concern when saying the UK will be zero carbon free by the year 2016 is that how will all the existing homes be replaced to become carbon free and energy efficient. When targeting the existing stock should they go down the road of demolition and also replacement?

The impact of embodied energy in demolition and also the replacement of homes is greatly outweighed by the energy saved in the use for efficient buildings. For a building to reach the achieved energy standards it is unrealistic to assume that a refurbishment can reach the same standard than a new build. In most if not all cases the better option would be demolition and rebuilding. There is the obvious reason such as social and structural not to demolish and rebuild but for developers, planners and clients they are all leaning towards new build for the reason of greater certainty in the result. New changes are also been proposed under Part L of the building regulations for 2010 regarding existing homes. It proposes to remove the 1000m thresholds for consequential improvements so that any addition to a building will require energy efficiency works to the existing property. This will also include conservatories in the regulations, so they would have to satisfy the same thermal criteria as other construction elements.

Achieving Code 6:

Code 3: This code consisted of carbon emissions been reduced by 25% over a basic standard home, a water consumption rate of 105Litres per person per day. The basic house also had just to reach the minimum building regulations, with the possible introduction of solar thermal panel and improvements to the fabric of the building.

Code 4: In stepping up to code level 4 the carbon emissions are reduced by 44% over a basic standard home. The home will have to consist of some renewable technologies possibly solar PV or Solar thermal, and also further improvements to the fabric of the building and also heat recovery. The introduction of wood pellet heating is also brought in at this stage.

Code 5: This is a further reducing in carbon emissions to a reduction of 100%, with the water consumption for a person per day down to 80Litres. A passive house building fabric should be introduced and a biomass boiler a very tangible and cost effective system to be put in. High performance windows, insulation and also air tightness should be achieved in this code along with also renewable electrical generation.

Code 6: Homes reaching this level will have approximately 145% carbon emission reduction over the basic standard home. There will be even more on site renewable electrical generation and will also continue on from code level 5 with high performance windows, insulation and air tightness, heat recovery and passive house building fabric.

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