There is no doubt climate change is real and it is happening and energy efficiency is a very important part of reaching the green house gases reduction goals. Certain drivers for improving energy efficiency are the obvious global climate change but also EU agenda and domestic policy imperatives.
In terms of energy efficiency measures for new construction work they are reflected within the Scottish building regulations with profound impact on the way dwellings are designed and also constructed with buildings been more highly insulated and having better heating system efficiencies than before. In meeting requirements related to reducing COÂ² emissions the Scottish government building standards commissioned a report "A low carbon building standards strategy for Scotland" (the Sullivan report) which outlined the government's approach to meeting its commitments on carbon reduction. The report outlined in terms of increasing the requirements on energy that by:
2010: Low carbon Standard, 30% better than 2007 regulations.
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2013: Very low carbon standard of 60% better than 2007 regulations.
2016: Net zero carbon in use.
2030: total life zero carbon domestic standards.
New building regulations have changes the energy efficiency standards and also the introduction from October 2010 the 2009 edition of the Standard Assessment Procedure (SAP), new buildings such as timber frame will have to be built to meet regulations to save more energy, have lower carbon emissions and also cost less to run.
1.0 Building Regulation Scenario:
Current requirements and standards within the Scottish Building regulations require that timber frame house specification must meet certain criteria. To show the compliance with these standards and requirements, in which the COÂ² emissions figure must be calculated according to the approved method. In the construction of the timber frame kit houses at present, the regulations in which the firm are working to are the revised building regulations of 2002 which were also amended in 2006, as part of this standard the firm will have been providing an energy rating to building control for the new homes using SAP (Standard Assessment Procedure). The intention of effective measures for the conservation of fuel and power in which are incorporated within timber frame buildings will not only lower the carbon dioxide emissions but the fuel poverty issues will be addresses to a certain degree.
From the implementation of recent improvements to the building regulations SAP is the only assessment in which is available for new timber frame dwellings. The SAP energy rating calculations have been required by building regulations since 1995 (SAP 2001) and from April 2006 the scope of the requirement has substantially increased (SAP 2005). SAP is a government based initiative in which the calculations demonstrate to building control authorities that the proposed dwelling meets the requirements of the building regulations. The SAP rating uses a large number of inputs for the calculation, taking into account nearly every element of the building such as the materials used in the construction of the building (Bricks/blocks/timber etc.) the thermal insulation material in which was proposed, the ventilation (Chimney/extractor fans/window ventilation) space heating systems and how they are controlled and the fuels used the heating system along with the lighting and also any proposed renewable energy technologies.
Results have estimated that within a typical domestic UK dwelling the energy use accounts for 27% of the notional carbon emissions. From the revision of the 2006 building regulations it has stipulated a 20% improvement factor over the previous 2002 standards. At the design stage this should be assessed by comparing the proposed new build with a notional building of the same size and form, with the notional building meeting all the minimum requirements of the building regulations. The SAP ratings form part of the design and should be undertaken before any final specifications are decided, in which the SAP calculation should be in two parts. In the design stage of a building a submission should be specified to building control to provide them with a "design stage" energy rating on the house, and a follow up assessment "as-built" with the inclusion of any variations which might have occurred during the construction and also the inclusion of a air pressure test result. The SAP calculation is expressed on a scale of between 1 and 100 with the higher the number the lower the fuel running costs, with 100 representing zero energy cost. SAP ratings can also be displayed in a system from A to G with the band A rated at 92 and above. New dwelling built would fall into the category of around 80 which would be band C.
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The air pressure teat is carried out as the dwelling approaches completion with the figures for the pressurisation test incorporated into the "as-built" calculation. The air pressure test is done to measure the amount of uncontrolled air leakage within the building, the test is only required in Scotland if a target figure better than 10mÂ³/h.mÂ² at 50 PA has been set. The SAP calculation will assume a certain amount of air leakage within a building, and also when building to assume that a test will be required so that methods are used to reduce air leakage. In demonstrating compliance with the building regulations air-tightness is one of the factors in which has to be considered when calculating both the TER (Target COÂ² emission rate) and also the DER (Dwelling COÂ² emission rate). The SAP model will compare the DER against the TER with the building only been compliant with the building regulations if the DER is equal to, or less than the TER. In achieving the TER the design air-tightness form dwelling should be higher than the limit of 10mÂ³/h.mÂ² at 50 PA.
If the building does not comply the house builder will have to undertake remedial work so the building does achieve the desired SAP rating. Once all has been agreed an "Energy Performance Certificate" (EPC) is completed to show the calculations carried out for the building regulations are compliant. The certificate can only be produced by an accredited consultant and will only merely highlight the potential performance of the dwelling. The certificate will be part of the "home information pack" which is a legal requirement for all house sales.
2.0 Current and Future Performance Assessment Metrics:
At Present the SAP 2005 calculations which are in use until October 2010 evaluates the whole of the building compared to the future calculations of SAP 2009, where they consider each individual element within a building. The future SAP 2009 methodology contains numerous changes which will affect the construction of new timber frame dwellings and to the designers, builders and also developers associated also. In regards to the DER and also TER of a timber frame dwellings, changes within SAP 2009 will affect both of them and will consequently be harder to achieve a zero carbon home.
The current situation in terms of energy consumption relates to a problem in which buildings at present are performing more poorly than they should, even when the builder/developer are complying with the requirements sought out in the building regulations. The essential gap between the predicted and realised energy performance comes from the study at Stamford brook which was under taken by the Leeds Metropolitan University which looked at the energy performance of a new masonry dwellings. The study showed that heat loss through party walls between two dwellings was due to thermal bypass effects not captured in the SAP modelling, with emissions also 10% higher than modelled due to the underperformance of fabric and building services within the dwellings.
When considering the effective changes within SAP 2009 there are essentially two types of change incorporated. These consisted of aiming to improve the accuracy of the SAP methodology and also to make the SAP calculations more flexible and enabling a variety of new and existing technologies to which are combined within a dwelling. Closing the performance gap and improving compliance with energy standards is an essential step for SAP 2009. SAP 2009 compared to 2005 standards in terms of party walls showed that SAP 2005 assumed heat loss through party walls to be zero, with the 2009 standard setting the U-value to be between 0.0 and 0.5W/mÂ²K. The study by Leeds Metropolitan University has now set a standard for developers to build to eliminate air-movement in which involves fully filling the cavity along with edge sealing along with adding a cavity sock.
From current standards in SAP 2005 the adaption of accredited construction details did not deliver buildings with the claimed thermal performance. It is therefore important that careful attention is given to details at junctions so that the continuity of both the insulation layer and also air barrier is maintained. Builders/developers have to take into account the provision for fuel and power and give consideration to the design and build ability of details, which will involve given evidence to the building control bodies that the necessary performance has been achieved. With the introduction of an accredited construction scheme it will benefit developers in their SAP modelling whereby they are using accredited details in which have actually been used. The approach will also encourage the take up of specific proprietary details which may be incorporated within a catalogue of accredited details of which may be specific in terms of component specification and provide also enhanced quality of the detail. The developer would have to register the detail to achieve a unique reference number to which can then be inputted into SAP, with random spot checks of development carried out to ensure that the accredited details were been used in practice. In the procedure for allowing the building control bodies to check the energy performance of new buildings the developer would have to provide the building control officers with a design stage submission with the SAP calculation as well as the component specifications which the developer is going to use. This will provide a greater emphasis on a list of key features generated by SAP which are important in delivering the TER of the building.
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With the new regulations coming into context the Target Carbon Dioxide Emission Rate (TER) and also the Dwelling Carbon Dioxide Emission Rate (DER) now have to be calculated prior to the building regulation drawings being submitted to building control. The Target Emission Rate is set to deliver 25% saving over the previous regulation; this is being lowered to bring a standard SAP assessment down to the level that of a code for sustainable home level 3.
SAP 2009 includes a significant revision in the assumed 40% increase in carbon-dioxide emissions of fuel used. This revision is encouraging the use of fuels such as biomass as it is seeing a reduction in emission factors with more incentives in place to use this kind of technology. From SAP 2005 to SAP 2009 a main change has taken place with the assumed hot water usage in a dwelling restricted to 125 litres of water per person per day imposed on all new builds, along with the comparison of only having one central heating system in SAP 2005 compared to two central heating systems or boilers on different fuels in SAP 2009. New innovative technologies were introduced in SAP 2005 which worked well but the inclusion of more than one system to be added at one time is incorporated within SAP 2009. Builders are encouraged to get the heating and cooling demand of a dwelling down with SAP 2009 including two ways which the lights, appliances and cooking can all contribute to heating the dwelling.
SAP Calculations for small room:
3.0 Future Proofing a Dwelling:
Within Timber frame buildings most of the energy used is for heating and also cooling the building. Energy efficiency and also occupant comfort are very important when it comes to the revision of any standards alongside the inclusion of lots of insulation and keeping the infiltration rates at a minimum while considering building and future energy budgets. Considerations such as high-performance windows/doors and the use of an energy efficient heating system are important in lowering the heating and cooling consumption and with keeping a building envelope as tight as possible, issues such as air quality in terms of vents and windows for in the inclusion of natural ventilation and also a mechanical ventilation system should be addressed in the construction of a timber frame building.
With the increasing need for energy efficiency associated with timber frame buildings, the inclusion of even deeper stud sizes within the envelope of a building are now been specified. At present the typical timber kit construction uses an 89mm x 44mm stud incorporating insulation between each stud. Future timber kit houses are moving towards using a 140mm x 47mm C16 stud with the increased depth allowing for more insulation to be incorporated which in turn will improve the energy efficiency. By assuming the typical timber frame kit house will be built in accordance with accredited construction details the typical timber dwelling will have an air-tightness measurement of 10mÂ³/hr/mÂ² at 50 Pascal's. High levels of infiltration from areas such as doors, windows and service penetrations directly affect the air-tightness of a timber frame building and will add to the heating and air conditioning loads while also to the COÂ² emission and energy bills associated with the building. Air leakage within a building accounts for 25-50% of heat loss and in achieving good air-tightness within timber frame dwelling will consequently reduce the capital spend on the heating and cooling systems used and while also reducing the running cost of the building and increasing the home comfort of the occupants. Timber frame systems have had a good record in achieving air-tightness within dwellings which was achieved by cutting out unwanted draughts. To continue this good standard and achieving a totally airtight dwelling the inclusion of a continuous air-resistant layer around the inside of the building such as, around the ground floor/external walls and roof sealing the inside of the building from outside will considerably help in reaching such targets. From developers prospective it is essential that procedures are in place to prove that the dwelling does meet the specific standards in air permeability, with the issue of air-tightness integral to thermal efficiency. It is seen though that undue emphasis on the issue of air tightness without relating back to the consideration of ventilation can directly affect the building in terms of it been very stuffy and also unhealthy. A solution to this problem can be the inclusion of a mechanical ventilation system within the building extracting the heat from the stale air and recycling it to warm the incoming fresh air. The inclusion of a mechanical heat recovery system can be seen to be more important than air-tighten a building as high humidity level and also warm environments can lead to the increase in dust mites which can exacerbate the onset of asthma and other respiratory infections so the more airtight a building is made the more need there is to ensure that adequate ventilation is maintained. The use of a whole house mechanical ventilation and heat recovery system was modelled combining air-tightness and showed improvements to 3mÂ³/h.mÂ² at 50 PA. There can be two systems employed when considering the use of mechanical heat ventilation which can comprise either of a central extract system of an individual room fan. Both of which should operate at a minimum rate to be as quite as possible and to recover sufficient heat to reduce, or dispense with, a conventional central heating system. In considering future standards air-tightness and ventilation should be coupled with each other to make significant contribution to performance standards and be kept under review in parallel with each other when considering changes to Part F (ventilation) and Part L (energy) while ensuring COÂ² reductions are not achieved at the expense of poor indoor air quality.
In achieving good thermal efficiency and U-value of any individual building element the minimization of thermal bridging is a major factor in doing so. The use of materials with inherently low thermal conductivity like timber and the prefabricated structure will contribute to controlling the thermal bridging of building elements. In the construction of timber frame buildings and in particular wall thermal bridging is usually caused by gaps in insulation layers within the fabric, structural elements such as lintels and frames and joints around elements such as windows and doors. The need to limit this heat loss through thermal bridging is becoming increasing important as more energy efficient buildings are made a requirement of building regulations. Incorrect detailing at the design stage and poor workmanship can have a significant effect on the issue of thermal bridging. Thermal bridging within timber frame buildings can be reduced and avoided by the use of exterior insulation, removing or insulating unnecessary structural elements and also more compact windows. It can also be reduced with the accommodation of good design and adopting the accredited construction details to the construction which would half the heat loss due to thermal bridges.
In the timber building the higher the insulation and thermal efficiency the less need there is for heating. In the typical building it is assumed that householders use a secondary heating system which would include systems such as electric, gas or solid fuel room heaters with a higher carbon burden than the main heating system. As dwellings such as timber frame they are becoming better insulated, secondary heating systems usage with primary system turn off will increase in future years. With this then in mind the standards might be subject to change on secondary heating to permit specifying a different proportion of the heating to be obtained from secondary systems. The aim of achieving 100% reduction of carbon emissions from Part L energy will therefore require the combination of a heating system such as biomass which achieves the highest COÂ² reduction for air permeability and also with the inclusion of Photovoltaic's to which would be the most cost effective option. Along with Photovoltaic's there are various other low or zero carbon technologies which would comfortably offer the technical potential to offset an increase in wall U-value from 0.35 W/mÂ²K to 0.25 W/mÂ²K. The inclusion of LZCT have shown to have had a reduction in emissions of at least 10% but however some technologies have a high capital cost and are not an attractive alternative to builders. SAP 2005 introduced the use of LZCT but for future calculations in SAP 2009 within timber frame dwelling the inclusion of innovative technologies for the carbon emission impact include solar water heating, photovoltaic's and also ground source heat pumps.
To a small Scottish construction firm there is no doubt that there is a need to change the way they are understanding what is ahead of them in terms of relevant building regulations, as the changes represent a major shift in thinking and also to the way dwellings are to be built. To the small firm additional benefits will include work from the provision of necessarily more specialised services which will be required to meet the changes.
The overall energy efficiency and sustainability within a timber frame building would possibility benefit from introducing higher penalties for builders/ developers who fail to meet energy standards and also if there was consideration to introducing a reduced or zero warrant fee for these designing to the future energy standards prior to their implementation. It is also highlighted that for homes such as timber frame to introduce future standards far more in advance to give small construction firms the possibility to become more familiar with the standards.
The introduction of the latest version of SAP is no doubt a major step in delivering the goal of zero carbon homes from 2016. From the introduction of SAP 2009 it will mean the calculation of energy demand is moving to a monthly basis, which will provide a more accurate assessment of energy use, with the other changes focusing on improving the accuracy of dwelling assessments. By designing to meet such targets and energy efficiency standards the use of accredited details will help significantly in assisting the designer to meet the required objectives. However there is the need to consider the need to stimulate a better uptake of energy efficiency and also the use of renewable energy technologies in achieving zero carbon.