Improving the energy performance of buildings has become increasingly important as the UK works towards achieving its net zero carbon emissions target by 2050. Households currently account for 40% of the UK’s total energy usage.
The government recently confirmed plans to ban fossil fuel heating systems such as gas boilers in new build homes after 2025 and proposed much tighter energy efficiency standards for existing housing.
In response to last year’s Future Homes Standard consultation, the government has set out plans to dramatically improve the energy performance of new homes to lower energy consumption and bills.
The Future Homes Standard will require new builds to not only be highly energy efficient, but to have low carbon systems in place in order to protect the environment and be zero carbon ready by 2025. They will be expected to produce 75-80% lower carbon emissions compared to current levels. From 2021 new builds will need to produce 31% lower carbon emissions to ensure industry is ready to meet the new standards by 2025.
So, before taking on your self-build project you need to consider what you can do to build an energy efficient dwelling.
SAP Calculations – Compliance with Building Regulations
Since 1995 SAP ratings have been required for all newly built dwellings under Part L of the building regulations. SAP stands for ‘Standard Assessment Procedure’ and is currently the only official, government approved system for assessing the energy rating for a new home. This can be a challenging aspect of the planning and building control process for many first-time self-builders and developers.
SAP calculations do three things:
- They demonstrate compliance with Part L of the building regulations
- They determine the SAP Rating which is the energy related running costs of a dwelling.
- They are used to produce an Energy Performance Certificate (EPC)
SAP assessors must be accredited and registered with a certification body. SAP ratings are only necessary for residential properties. In England, SAP calculations measure two elements: the Dwelling Emission Rate (DER) and the Dwelling Fabric Energy Efficiency (DFEE). The calculations determine a Target Emissions Rate (TER) and a Target Fabric Energy Efficiency (TFEE) rate. The DER and DFEE must be lower than the TER and the TFEE. In Wales and Scotland, the report only measures the DER, although building regulations are stricter.
The main purpose of SAP calculations for L1A (new builds) is to produce an Energy Performance Certificate (EPC).
In order to carry out SAP calculations for your new build you will need as much information about the following as possible:
- Site plans
- U-value of openings
- Insulation type/thickness
- Hot water generation
- Specification of heating systems
- Specification of ventilation system
- Percentage of low energy lighting
- Accredited construction details
- Renewable technologies
In order to rent or sell a residential home you must by law have an EPC. The EPC rates properties between a G (worst performance) to an A (best) across two measures, energy efficiency and environmental impact.
For new builds SAP calculations are divided into two reports: ‘design stage’ and ‘as built’.
What’s Involved in the Design Stage Report?
- Before building begins, the construction details of the property need to be assessed and approved.
- The data acquired from the first step is input into calculation software in order to produce TER and TFEE rates and to demonstrate that the building is DER and DFEE compliant.
- A ‘predicted’ energy assessment is then produced.
What’s Involved in the ‘As Built’ Report?
- The construction details are reassessed once the building is complete and any final details taken into account such as heat pump model or air tightness score.
- The final report produces the EPC.
It is advisable to enlist the help of a specialist when embarking on building your eco home. Professionals such as architects with experience in energy efficient self-builds can help you with the different processes you will need to incorporate into the design of your self-build.
Before you begin the building process you need to think about what principles can be integrated into the design and build stages of your Self Build to make it truly energy efficient.
Passivhaus Principle And The ‘Fabric First’ Approach
During your research on energy efficient building methods, you may well have come across the term ‘Passivhaus’. The Passivhaus standard originated in Germany during the 1990s with the aim of vastly reducing the energy usage of homes. The standard focuses attention on the design and construction stages of the build process. It very purposefully concentrates on getting the fabric of the building right in order to significantly lower the building’s energy usage.
A strict set of criteria is adhered to in the design and construction of a Passivhaus building to ensure maximum comfort with minimum overall energy consumption. The building fabric is detailed in such a way that heat loss is reduced to an absolute minimum, whilst internal heat gains are maximised. As a result, conventional heating systems can be removed, and space heating can sufficiently be supplied through passive sources such as such as body heat and the sun.
The definition of Passivhaus is driven by air quality and comfort. The Passivhaus Institute describe it as the following:
“A Passivhaus is a building in which thermal comfort can be achieved solely by post-heating or post-cooling the fresh air flow required for a good indoor air quality, without the need for additional recirculation of air.”
Working towards achieving Passivhaus standards is not about buying lots of fancy renewable energy gadgets. It’s all about changing the way you approach building.
During the design stage it is important to look at ways of radically reducing air leakage, getting rid of thermal bridges, increasing insulation levels, and making good use of glazing for solar gain. Thermal bridges should be avoided whenever possible. Proper planning, design and construction are essential to help identify and remedy thermal bridges. A thermal bridge is when escaping heat follows the path of least resistance. Thermal bridging generally occurs when there is a break in, or penetration of the building envelope (e.g., insulation) such as junctions between the wall and the floor or holes in the building envelope for pipes and cables etc.
Throughout the build stages, it is vital that your construction team works closely with one another to complete each stage without costly mistakes. In order to complete a certified Passivhaus you must engage a certified Passivhaus designer who is a specialist in designing and certifying your self-build. However, you can aim to follow the principles of Passivhaus without gaining the certification as some Passivhaus requirements such as triple glazing might fall outside your budget. Creating as airtight a property as possible will go a long way in building an energy-efficient home.
The Passivhaus or ‘Fabric First’ approach aims to minimise your self-build’s reliance energy consumption by concentrating solely on getting the most out of the fabric of the building. The airtightness of your self-build is without doubt the most important step to achieving an energy efficient, ‘Fabric First’ self-build dwelling.
Airtightness And Insulation
Some of the most efficient construction methods to ensure a high level of airtightness in your self-build include timber frame, structural insulated panels, insulated concrete framework and cross laminated timber. If you’re using slightly less efficient methods such as brick and block you can still increase their airtightness levels through the use of tapes and membranes.
Whatever construction method you choose you will need to enhance your self-build’s airtightness with super-high insulation. The more airtight your construction, the more your home will retain warm air and the less energy your building will consume through heating.
Though there are no hard and fast rules for what superinsulation is, in order to be super-insulated you would need to be insulated to a U-value of 0.15 watts per square metre kelvin in the walls and 0.1 in the roof. The U-value is the rate at which heat passes through the insulation. It should be no more than 0.30 watts per square metre kelvin and the lower the better.
It’s extremely important to get glazing right when you are trying to achieve an energy efficient self-build. Glass not only lets energy pass through it from the sun’s rays trapping in the subsequent heat but allows natural daylight in too meaning less reliance on electrical lights. However, once the sun sets glass can release heat energy quite quickly and so to improve your home’s heat retaining abilities it’s vital to install double-glazing or triple glazing. Your energy efficient self-build should contain enough glass to benefit from the sun’s free heat and natural daylight as possible but not so much that your home is too warm in the summer and too cold in the winter.
The sun’s contribution to a building’s internal heat is called ‘solar gain’. To make the most of this standard, your design should aim to maximise the solar gain in the winter and minimise it in the summer. So, it is most important for you to concentrate on your self-build’s glazing, orientation, and thermal mass at the design stage. If triple glazing is too expensive for your project, the best alternative is to use high-performance argon or crypton filled double glazing units.
To fulfil Passivhaus standards you would need to seal the gaps between glass panes and fill with argon or krypton gas to make them as airtight as possible. Further to this you could also use ‘low emissivity’ coating, ‘warm edge’ glass spacers and specially adapted window frames.
As the direction and height of the sun changes considerably throughout the year in Northern latitudes such as the UK it’s important to consider the position of your self-build and which direction it faces as this can impact the efficiency of your glazing significantly. Surfaces facing south receive sun all the year round and so it is recommended that any windows used for maximising solar gain should face south or as close to south as possible. North-facing surfaces lie in shade all the year round, in fact the North-East to North-West quadrant receives very little sun except at the peak of summer. For this reason, it is best to keep glazing to a minimum on this side of the building and focus more on good quality insulation when designing your energy efficient home.
A material’s thermal mass is, fundamentally, its ability to absorb and store heat. This is something that can be put to good use in the design of your self-build. If a building has a high thermal mass, it will take a long time to heat up and a long time to cool down which results in a very steady internal temperature. In contrast, if a building has a low thermal mass, it will be subject to wide fluctuations in its internal heat. The best heat-storing materials are those with more density and therefore heat up slowly. As they heat up slowly, they distribute their heat gradually. Materials such as brick, concrete and stone have a high thermal capacity and are the foremost contributors to the thermal mass of a house. Water also has a very high thermal capacity and is well suited to central heating systems. Air, on the other hand has quite a low thermal capacity and although it warms up quickly, it does not maintain its heat for very long. Once walls and floors are warm, only then will air maintain its heat. For this reason, investing in the fabric of your self-build is paramount to reaching a great energy efficiency rating. It’s crucial that you spend time considering which methods of construction you would like to integrate into your design so that you can develop the highest thermal mass possible.
Powering Your Self-Build
Having carefully considered the fabric of your self-build you will need to spend some time looking into how you are going to heat and power your home. There are a number of systems which can be utilised effectively to maintain energy efficiency.
Mechanical Ventilation Heat Recovery Systems
A Mechanical Ventilation with Heat Recovery (MVHR) system is the perfect way to ventilate and heat a sufficiently airtight house. You can reuse as much as 95% of heat that would have otherwise been lost. This network of ducting connects each to a heat recovery system stationed within the warmer part of your house.
The MVHR system works by continuously extracting warmer air form the wet rooms of the house at the same time as drawing fresh air inwards form outside. The heat from the extracted air is recycled through a heat exchanger within the heat recovery unit and is reused to temper the fresh air supply for the habitable rooms of your house such as the bedrooms and living spaces. In the summer, a special by-pass function helps to ensure comfortable temperatures are maintained indoors. This function switches off the heat recovery system at intervals meaning more cool, fresh air can enter the building to lower temperatures gradually.
Your self-build could benefit significantly from the use of a solar panel electricity system. Solar photovoltaics (PV) capture the sun’s energy using photovoltaic cells. Remarkably solar photovoltaics do not require direct sunlight to work which means that you can still generate energy on cloudy days. The electricity produced can be used to run everyday appliances and lighting.
Another way to make the most of natural energy to heat your home is through the use of heat pumps. They work by extracting heat contained within earth, air, or water, depending on which system you choose. Being reasonably straightforward to install, air source heat pumps are a cheaper option than the ground source heat pump. Ground source heat pumps require a large space in your garden to install the loops within the ground. They do however last around 25 years and require almost no maintenance.
Energy Storage Systems
It is not always possible to get a consistent and predictable level of supply from renewable energy systems so it’s worth investigating the range of products that act as batteries. Batteries can store energy when it is available and release it when needed. This has quite a significant impact, as the efficiency of domestic systems can be improved by as much as 50%.
It’s vital that new homes are built to be as low carbon as possible. With the UK’s net zero carbon target for 2050 set in law, clearly the most cost-effective approach is to build today’s new homes so they can hit a carbon neutral standard, without the need for further retrofitting.
As you can see there are many ways to make your self-build energy efficient. However, the degree to which your self-build is energy efficient will depend on a number of factors which we have covered briefly above.