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Numerous local authorities are committed to constructing buildings to net-zero carbon emissions performance, and have declared carbon emergency, striving to reach carbon neutrality well before 2050. However, buildings in the UK are currently being designed and constructed to current building regulations which do not require net-zero performance, and these buildings will last well beyond 2050. This paper presents a case study of a housing development in Hertfordshire, UK, where a structured approach for achieving net-zero carbon performance homes was developed. The methodology was based on dynamic simulation modelling to design buildings which achieve net-zero operational emissions, and an industry standard inventory of carbon and energy database was used to evaluate embodied emissions in building materials. The approach comprised of developing dynamic simulation models to investigate the improvement in energy performance of the development through fabric-first approach, focusing on building envelope design prior to introducing renewable energy systems, in order to achieve operational net-zero carbon performance. Carbon emissions (operational and embodied) were investigated to assess the appropriateness of the deployed strategies. Dynamic simulation results combined with embodied emissions analysis illustrated that, by combining embodied and operational emissions, a net-zero carbon performance would be achievable by the 2050 target only if alternative building materials based on photosynthetic bio-composites are used. This analysis also highlighted the limitations of conventional retrofit interventions carried out 10 years after the construction as they resulted in increased embodied carbon emissions, thus lengthening the time period well beyond the 2050 target for achieving net-zero carbon performance. As the use of conventional materials appeared to delay the achievement of net-zero emissions by several decades, the only way to achieve net-zero targets before 2050 is to design new buildings to be carbon negative from the operational point of view and to use photosynthetic materials for their construction.
The current regulations for UK housing construction do not require the new buildings to be designed and built to net-zero emissions.
Therefore, we are in a challenging situation where new buildings, which will last well beyond 2050, are being designed and built to far lower standards than net-zero. As 80% of the 2050 building stock already exists (
Thus, an urgent matter for policy change at local and central government planning guidance levels is needed to introduce a requirement for net-zero design of new buildings and for net-zero retrofit of existing buildings in order to help the UK achieve zero emissions targets by 2050. Some initiatives are starting to emerge, including the RIBA’s climate change plan (
The UK building stock is one of the oldest in Europe and accounts for nearly 40% of the nation’s total carbon emissions (
Thus, a specific objective of this work is to investigate the requirements for achieving net zero emissions from new buildings by 2050. As carbon emissions from newly constructed buildings occur as result of emissions embodied in building materials and emissions arising from the operation of the building, the main research question is:
how to bring UK housing projects in line with net zero emissions targets, taking into account the combined embodied and operational emissions?
There have been many barriers to achieving zero carbon buildings, net zero energy buildings, or nearly zero-energy buildings. Most of the previous work has focused on case studies of specific projects or specific aspects of building performance, rather than on fundamental principles and integration of these principles into holistic designs. Thus, a study on “Energy Performance Assessment of a 2nd-Generation Vacuum Double Glazing” (
Despite the body of previous work, there appears to be a gap in the holistic “how to” studies in the field of zero carbon buildings, net zero energy buildings, or nearly zero-energy buildings. That gap was overcome by the structured approach introduced in “Designing Zero Carbon Buildings Using Dynamic Simulation Methods” (
Research undertaken by the Environment Audit Committee (EAC) (
Research by BEIS suggests (
This indicates the need for a structured approach towards developing and delivering net-zero carbon performance solution, to meet the 2050 target specified by the UK government.
The focus of this research is to investigates how UK housing projects can be brought in line with net-zero targets. The choice of the Case Study was based on the specific grant funding received for this project and on the availability of a scheme approved for construction by the Planning Department of the collaborating local authority in Hertfordshire. The scope was limited to one scheme only based on available funding. Thus, a housing development with complete planning permissions was identified in England and selected as a candidate for investigation of requirements for requirements of bringing UK housing projects in line with net-zero targets.
The development is comprised of six homes of which two homes are semi-terrace and four homes are mid-terrace. It has a total footprint of 330 m2 and each home has an area of 94 m2. The typology of the development is six three-bedroom homes spread over two storeys (ground and first floor), with North–South orientation. The construction technology of the building was assumed to be of conventional concrete blockwork and brick masonry, with adequate amount of insulation in the cavity and air-tightness levels to meet minimum current UK building regulations Part L specifications,
Standard specifications of various Building Regulations.
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Wall | 0.28 | ≤0.15 | 0.10 |
Floor | 0.22 | ≤0.15 | 0.10 |
Roof | 0.16 | ≤0.15 | 0.10 |
Glazing (Double) | 1.6 | ≤0.80 | 0.80 |
Air Tightness | 2.27 @ 50 Pa | <0.6 @ 50 Pa | 0.60 @ 50 Pa |
New houses, or new dwellings as they are called in the UK Building Regulations, need to comply with Part L of the Regulations specified in Approved Document L1A (
This study uses building performance simulation, which is the only way to explain and evaluate the complex ways of interaction between the building, its occupants and the climate. The simulation is conducted over every hour of the simulation year, namely 8760 hours, using weather data for the particular location, and slicing the simulation timestep to as low as 10-min intervals whilst dealing with significant complexity of heat and energy transfer in and around the building. As building performance simulation is a universal method based on the first principles, there is an implicit information regarding the generalizability, reliability, and versatility of the study to be applicable to the other context and/or countries.
The solar geometry used in the simulation was for the location of London Luton, Latitude 51.88°N, Longitude 0.37°W. The weather data was for London Kew example weather year (Kew.fwt), sourced within the IESVE simulation software (
Climate Change Committee (CCC) defines net-zero as the 100% reduction in operational emissions (
To investigate the energy performance of the housing development used as a case study, dynamic simulation models were developed, using an industry standard tool from Integrated Environment Solutions called Virtual Environment IES-VE (
Model geometry of the building was developed in IES-VE 2021 and building geometry and construction details were specified in the model,
IES–VE model of the housing development
Once the model was developed to satisfactory detail, analysis of the building was undertaken to assess the baseline performance. This was the starting point for the development, termed as Case A—Built to planning approval. Several iterations of the model were developed, investigating the energy performance in response to strategic treatment of the building. This was achieved by following a fabric-first approach, to improve the performance of the building using passive measures and then employing use of active low-carbon measures such as heat-pumps, PV modules etc.
The energy efficiency improvement process of the building was split into four stages; 1) Building fabric improvement, 2) Building systems improvement, 3) Renewable energy strategy, and 4) Internal thermal comfort analysis.
To maximise energy efficiency through passive measures, building fabric was selected as the first point of focus. Through iterations of the Case A model, energy efficiency of the building fabric was improved to meet the zero-carbon performance U-values,
This model was further utilised to improve the building systems of the housing development. Building systems such as lighting and domestic hot water (DHW) were specified as systems defaults using fluorescent lights and gas heated water with system default sizing. Space heating systems were changed from system default gas boilers to represent air-source heat pumps to match closely with the aim of the developers. Lighting systems were improved to represent LED lighting and DHW consumption was adjusted to reflect a rate of 5L/person/hr therefore 120 L/person/day, apportioned across wet rooms only (bathroom/kitchen/toilet).
Once satisfactory reductions in carbon emissions and energy demand were obtained from improving building systems, it was necessary to improve the energy strategy for the housing development so that its energy demand would be met using renewable sources. This was accomplished using Photovoltaic (PV) modules, which were added to meet the energy demand of the building. As shown in
Renewable energy sources: photovoltaic solar panels placed on the roof and solar thermal panels placed vertically on the south facing wall.
Once an operational zero carbon performance model was achieved, it was termed as Case B—Zero carbon performance model. This served as the second performance reference point for the housing development. This was later used for developing a cumulative carbon analysis for the housing development, as discussed in the next section.
In order to assess the environmental impact of the building, a Lifecycle Carbon Assessment (LCA) approach was utilised, to quantify the carbon footprint of the building until 2050, in line with the UK government target of achieving net-zero performance.
This was done through the use of embodied carbon emissions values from Inventory of Carbon Emissions (
To investigate the environmental impact and carbon footprint of the building, four key scenarios were investigated; Case A—Built to planning approval, Case B—Zero carbon performance, Case C—Zero carbon retrofit of Case A in 10 years, and Case B.1—Net-zero carbon design using hemp-lime construction. This was done in order to draw parallels between the different approaches for the construction of the building.
For each scenario, total embodied carbon emissions of the building were calculated, and a cumulative total was established by adding annual operational emissions, which were in fact slightly negative, to the embodied emissions. This was done in order to identify the time period required to achieve net-zero carbon performance in each case. Observations and results from this step are discussed in the main results section of this paper.
It is worth noting that the simulation models in this analysis could not be calibrated and validated, as they were based on non-existing buildings with no opportunity to get actual performance data for calibration. As previous research shows (
Preliminary analysis of the building (Case A—As built to planning approval) revealed significant areas for improvement, in order to achieve a zero carbon performance as in Case B—Zero carbon performance, as shown in
Areas of improvement to achieve zero carbon performance.
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Wall | 0.28 | 0.11 | 0.11 | 0.11 | |
Floor | 0.22 | 0.11 | 0.11 | 0.11 | |
Roof | 0.16 | 0.10 | 0.10 | 0.10 | |
Windows | 1.6 | 0.91 | 0.91 | 0.91 | |
Airtightness | 2.27 ach |
0.6 ach |
0.6 ach |
0.6 ach |
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Heating | Air source heat pumps | Air source heat pumps | Air source heat pumps | Air source heat pumps | |
Cooling | Natural Ventilation | Natural Ventilation | Natural Ventilation | Natural Ventilation | |
Lighting | Fluorescent | LED Lighting | LED Lighting | LED Lighting | |
Energy and Renewables | Grid Electricity | PV Modules | PV Modules | PV Modules |
Air changes per hour.
Results from the dynamic simulation illustrate significant improvement in the energy efficiency of the building as it was able to achieve zero carbon emissions in its operations as in Case B, shown
Energy performance in Case A—designed to planning approval and Case B—designed to zero carbon performance.
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Energy Performance (MWh) | 65.640 | −6.978 | −6.860 | −6.974 |
Carbon Emissions (kgCO2) | 34,071 | −3,622 | −3,560 | −3,619 |
Cumulative carbon emissions analysis of the building revealed key insights into the ability of the building to achieve a true net-zero carbon performance status. The research found that, of the four scenarios investigated, only two scenarios, Case B and Case B.1, were able to achieve a true net-zero carbon performance, before the end of this century. Out of these two cases, only one scenario, Case B.1, was able to achieve net-zero carbon performance before the target date of 2050,
Embodied and Operational Carbon Emissions of the four different cases analyzed.
This analysis provides evidence to support that embodied emissions can delay the achievement of net-zero emissions by 3 decades.
This paper has presented a case study where net-zero carbon performance was achieved through 100% reduction of operational carbon emissions, and gradual reduction of embodied emissions based on negative operational emissions over several decades. To achieve this, the research utilised a three-step approach; 1) Be Lean: Use of less Energy—achieved through careful implementation of passive design strategies, 2) Be Clean: Supply energy efficiently—achieved through careful selection and implementation of active measures such as lighting, HVAC systems etc., and 3) Be Green: Use of renewable energy systems—achieved through careful use of appropriate renewable energy technologies such as PV panels, solar hot water systems etc.
To achieve a net-zero carbon performance target, it was crucial for a building to first achieve operational zero carbon performance. After numerous simulation runs, with net-zero operational carbon emissions set as a target and improving the thermal insulation envelope between each simulation run, this was achieved by the set of parameters shown in
Research suggests (
The impact of embodied carbon emissions on cumulative carbon emissions, operational and embodied, is plotted for the four scenarios: Case A, Case B, Case B.1 and Case C in
Of the four scenarios explored in this paper, only one scenario—Case B.1—Net-zero carbon design using hemp-lime construction—presented promising results for achieving net-zero carbon before the target date of 2050 set by the Climate Change Act. This was achieved through the use of natural materials—in this case hemp-lime bio-composite. This material is able to provide significantly low embodied carbon values through carbon sequestration in the plant material during its growth, with negative emissions of −108 kgCO2/m3 (
In comparison, Case B—Zero carbon performance model built from conventional materials, was also able to achieve negative emissions of −3.33 kgCO2/m2 in 2065, 15 years past the 2050 target. In Case A, we observed that due to the energy inefficiency nature of the building fabric leading to high energy consumption and therefore high operational carbon emissions compounding each year, it required significant improvements to the building fabric to achieve a net-zero carbon performance.
We wanted to investigate what would have happened happen if Case A had been retrofitted to a zero-carbon performance level. This scenario is explored in Case C—Case A retrofit in 10 years i.e., 2031, where we observe a spike in the cumulative carbon emissions of the building–from 535.85 to 587.8 kgCO2/m2, arising from embodied emissions in retrofitted materials.
After the retrofit of the building to operational zero carbon performance, cumulative carbon emission value starts reducing each year. However, despite achieving operational zero carbon performance in 2031, achieving net-zero carbon performance was not possible by 2050. This was because the cumulative carbon emissions compounded up to the year 2031, set a higher starting point for achieving a net-zero carbon performance. Hence, operational reductions in carbon emissions were not adequate to offset the high starting point. Thereby the building was on track to achieving net-zero carbon performance in the next century, which is significantly later than the target year.
In parallel with cumulative carbon emissions, we wanted to explore the cost implications of the net-zero carbon retrofit process. We used a Lifecycle Cost Analysis approach for the building to investigate the trade-offs between building to net-zero carbon emissions and retrofitting at a later stage. To develop this, the costs of building materials utilised were obtained through the open market for each material and inflation was assumed to be at 3%. We found that the most cost-effective approach towards developing net-zero carbon buildings was through Case B and Case B.1 as illustrated in
Investment and Cumulative Operational Cost of the four different cases analysed.
Costs of improvements to achieve zero carbon performance.
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Walls (£) | 27,484 | 36,826 | 81,947 | 57,372 |
Roof (Rafter Level) (£) | 44,815 | 53,499 | 69,067 | 53,500 |
Floors (£) | 79,067 | 89,630 | 113,739 | 89,630 |
Glazing Components (£) | 140,000 | 176,000 | 181,280 | 176,000 |
PV Modules (£) | — | 16,244 | 16,244 | 16,244 |
Solar Thermal Panels (£) | — | 22,891 | 22,891 | 22,891 |
Air-source heat pumps (ASHP) (£) | 10,000 | 10,000 | 10,000 | 10,000 |
Pod-Point Electric Car Charger (£) | - | 529 | 529 | 529 |
Total Costs (£) | 301,366 | 405,619 | Case A+ 194,331 | 426,166 |
Percentage increase of cost from Case A | 35% | 65% | 41% |
How do these results compare between the four different cases and with other performance criteria? This is summarised in
Performance comparison.
Measure | Comparison | Case A | Case B | Case C | Case B.1 |
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Operational energy use (kWh/m2.yr) | UK Part L 2021 = 120 | 69.31 | 12.95 | In 2021: 69.31 | 12.96 |
Passivhaus <60 | In 2031: 13.08 | ||||
RIBA 2030 < 35 | |||||
Operational emissions (kgCO2e/m2) | RIBA 2030 : Net 0 offset | 35.98 | −3.82 | In 2021: 35.98 in 2031: −3.76 | −3.82 |
Starting embodied emissions (kgCO2e/m2) | RIBA 2030 < 625 kgCO2e/m2.yr | 176.10 | 161.12 | 176.10 | 82.65 |
Net zero reached (year) | Never | 2065 | Well beyond 2100 | 2043 | |
Embodied emissions at 60 years (kgCO2e/m2) | RIBA 2030: Net 0 offset (60 yr) | 2334.61 | −64.52 | 347.90 | −146.82 |
As it can be seen from this table, in terms of operational energy, UK Building Regulations (UK Part L 2021) require energy performance of 120 kWh/m2.yr or less. The Pssivhaus standard requires less than 60 kWh/m2.yr and RIBA 2030 requires less than 30 kWh/m2.yr. Case A, is close to Part L 2021, and cases B and B1 exceed this performance by significant amount. Case C starts the same as Case A and after the retrofit in 10 years it is aligned with Cases B and B1.
In terms of operational emissions, RIBA 2030 requires net zero operational emissions, whilst Case A is high above that. Cases B and B.1 exceed RIBA 2030 requirements, performing at negative emissions. Case C starts with the same emissions as Case A in 20201 and it aligns with Cases B and B.1 after the retrofit in 10 years.
The starting embodied emissions in all cases are lower than the RIBA 2030 requirement of less than 625 kgCO2e/m2.yr. However, in Case C after the retrofit in 2031 the embodied emissions increase to 899.79 kgCO2e/m2.yr, well above the RIBA 2030 threshold. Due to positive operational emissions in Case A, net zero is never reached. In cases B and B.1 net zero is reached in 2065 and 2043, respectively. In Case C, net zero is not reached even well beyond 2100.
At the 60 years mark defined by the RICS as the extent of the building lifetime, Case A will have accumulated nearly 4000 kgCO2e/m2.yr and Case C nearly 600 kgCO2e/m2.yr, whereas Cases B and B.1 will have accumulated negative emissions of −108 kgCO2e/m2.yr and −246 kgCO2e/m2.yr, respectively.
As these results show, the design that fulfils the objective of reaching net zero by 2050 is Case B.1, designed for negative operational emissions and constructed with hemp-lime bio-composite material.
As it can be seen from
It is worth pointing out why the embodied emissions depend so much on the choice of materials used in construction. For instance, 1 m3 of brick will have embodied emissions of around 357 kgCO2/m3 depending on the brick type and concrete will have embodied emissions of around 3507 kgCO2/m3 depending on the concrete type (
What other barriers could impact the achievement and development of net-zero carbon performance buildings? This research recognises that factors such as user-behaviour, building systems design and performance, skills-gap and the design of the building impact highly on the performance of the building. To alleviate such issues, the research team believes that it is crucial that there is an early collaboration between the design team and building physics analysis team and with other suppliers and manufacturers, thereby empowering built-environment professionals with the knowledge to achieve net-zero carbon performance buildings. The research team has undertaken post-occupancy monitoring and analysis of several homes across the UK such as the Zero Carbon House in Birmingham and believes that building performance can be optimised by developing a strong understanding of the user-behaviour through post-occupancy monitoring and providing the user a strong understanding of how to optimally utilise the building to meet their operational and thermal comfort needs.
Another barrier to better carbon emissions performance is the increased cost of low carbon solutions. As it can be seen from the last row of
What can different stakeholders, including Quantity Surveyors and other professionals, take from this research? In order to bring climate change under control, it is a responsibility of all professions involved in building design and construction to become familiar with the consequences of embodied emissions arising from construction materials. Ignoring these consequences can lead to a point of no return as far as climate change is concerned. Various professional bodies need to include these findings into their continuing professional development courses and make such courses mandatory for a license to practice their respective professions.
What are the sectoral and policy challenges associated with delivering building of this nature in practice, including design team perceptions? Delivering hemp-lime buildings is not new and useful practical lessons have been learnt, as reported by
What might be the recommendations around energy strategy and operations? What are the implications and opportunities of scale of construction? The work by
What policies and incentives could be suggested to local and central planning guidance levels? The research recognises that some local councils in the UK have issued mandate for all developments, to improve their performance beyond Part L standards, in form of a supplementary planning guidance document (SPG) such as those issued by the Greater London Authority (GLA). This research shows that a similar type of policy change, outlining the requirements to meet net-zero carbon levels through use of low-embodied materials such as hemp-lime bio composite as well as use of the three step hierarchy strategy discussed earlier in this paper, would empower the industry professionals with holistic guidance for design and development of new net-zero carbon performance buildings and develop net-zero carbon retrofit solutions.
Are there any wider benefits to society? As hemp-lime material is not yet widely used, opportunities exist developing new skilled construction personnel. As the material is fire resistant, its application to high-rise apartment blocks could lead to safer buildings. In this particular context, there are gaps, as well as opportunities. There is an opportunity for new research and development into application of this material as retrofitted insulation on tall facades, with 3D printers redeveloped for vertical 2D printing along the facade. As hemp-lime is not a load-bearing material, there are opportunities for further research into the application of natural fibres to improve its structural properties. However, the most significant societal benefit is the ability of this material to help with bringing climate change under control if used more widely.
Whilst the strength of this study is in highlighting the importance of embodied emissions as a contributor to the overall emissions in newly constructed buildings, a weakness of this study is that it is based on a single case of a cluster of six family homes in Hertfordshire, United Kingdom. However, in order to find this case, the research team had to secure funding for this work, establish a working relationship with a local borough council, and then to find a suitable project that had received a planning approval to be constructed. With more funding and time, more suitable cases could have been found and analysed. However, on balance, we believe that this weakness has been outweighed by the strength of highlighting the scale of efforts needed in the UK and beyond to achieve net zero by 2050.
This study used an example of a housing development in Hertfordshire, which was approved for construction by the Planning Department of the collaborating local authority. As the current Building Regulations in the UK do not require new houses to be built to net-zero standards, and as the local authority in question declared carbon emergency and their aim to become carbon neutral by 2030, the study investigated how this could be achieved by alternative designs in comparison with the design that was approved for planning.
Building performance simulation was used as the basis for designing zero carbon operational performance based on the methods developed by
The study demonstrates that achieving net-zero carbon design by 2050 is possible, but only through design for operational negative emissions and the use of natural photosynthetic materials such as hemp-lime bio-composite. Through cost analysis, this work also illustrates that using natural materials with very low or negative embodied carbon emissions results in lower cumulative carbon emissions and therefore can provide an easier pathway towards achieving net-zero carbon performance buildings to be achieved sooner despite higher initial costs in comparison to conventional solutions, which have shown to prolong the achievement of net-zero carbon performance.
The use of conventional materials appeared to delay the achievement of net-zero emissions by several decades, either in construction of new or in retrofit of existing buildings. One of the most important conclusions is therefore that while the UK Building Regulations are not yet adequate for achieving carbon neutrality and do not completely restrict the use of fossil fuels, the only way to achieve net-zero targets before 2050 in new buildings is to design them to be carbon negative from the operational point of view and to use photosynthetic materials with negative embodied emissions for their construction.
Future studies will focus on salability of the presented solution, and on accelerating the adoption of net zero designs by developing preset designs for specific building archetypes.
The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.
Conceptualization, LJ and SC; methodology, LJ and PB; investigation, LJ, PB, and SC; writing—original draft preparation, PB, LJ and SC; writing—review and editing, LJ and SC.
This study was funded by a grant from Research England
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
The authors gratefully acknowledge the collaboration with, and the help and support from the Welwyn Hatfield Borough Council through the provision of information relevant for this project.