Looking at whether detailed specifications and adjustments to energy requirements in planning policy could encourage developers to deliver Net Zero standard new homes.
At a glance
Housing Advisers Programme case study
2020/21 cohort
Executive summary
In July 2019 the Isle of Wight Council passed a Climate Emergency Declaration and made a commitment to collaborate with partners to reduce the island’s carbon emissions to zero by 2040.
This research project brought together the Isle of Wight Council’s regeneration, sustainability and planning teams with the island’s largest housing association. It looks at whether detailed specifications and adjustments to energy requirements in planning policy could stimulate developers to deliver Zero Carbon Standard new homes to benefit our residents and community without reducing the supply of new housing.
Challenge and context
The Isle of Wight has significant housing need and development challenges. The challenge is to assess whether introducing a specification for carbon neutral homes in our local planning policy to minimize the Island’s future carbon burden, could pose risks for the viability of development of much needed housing.
What we did
We commissioned research on the technical and cost implications as a pilot for future developments to:
- improve the quality of homes, making them more energy efficient
- reduce energy bills, reducing the risk of fuel poverty
- build to high standards including good ventilation to reduce the risk of overheating and of damp, mould, condensation and related respiratory conditions
- reduce our carbon footprint and improve air quality.
The research
This project was a partnership between the Isle of Wight Council’s regeneration, planning and sustainability teams and the island’s largest housing association, Southern Housing Group, working with Etude sustainability engineers, Levitt Bernstein architects, Currie and Brown design and construction consultancy and Elementa green engineering consultants.
Energy efficient options
We looked at energy efficiency improvements that could be made to new homes on the Isle of Wight to meet the London Energy Transformation Initiative (LETI)’s Climate Emergency Design Guide, which outlines the KPIs of new buildings to ensure our emissions reduction targets are met.
|
Key performance indicators |
Space heating demand (15kWh/m/yr) |
Energy use intensity (EUI) (35 kWh/m/yr) |
Energy balance (Net zero balance) |
Upfront embodied carbon (varies with typology) (300 COe/m/yr) |
|---|---|---|---|---|
|
Climate Change Committee recommendation |
Yes |
No |
No |
No |
|
LETI net zero definition |
Yes |
Yes |
Yes |
Yes |
|
Alignment with Passivhaus |
Yes |
Yes |
No |
No |
|
Reduces heating, energy and bills |
Yes |
Yes |
Yes |
No |
|
Reduces peak energy demand |
Yes |
Yes |
No |
No |
|
Allows for load shifting and energy flexibility |
Yes |
Yes |
No |
No |
|
Compatible with different heating systems |
Yes |
Yes |
Yes |
No |
|
Less renewable energy required to achieve zero energy balance |
Yes |
Yes |
No |
No |
|
Addresses fuel poverty |
Yes |
Yes |
Yes |
No |
|
Contributes to a healthy indoor environment |
Yes |
No |
No |
No |
|
Reduces overall carbon emitted |
Yes |
Yes |
Yes |
Yes |
LETI recommends:
- New homes must be designed to be net zero carbon.
- New homes must be ultra-low energy (extremely energy efficient)
- New homes must be heated by low-carbon heat – e.g. heat pumps. There should be no gas boilers installed in new homes.
We looked at five housing typologies common on the Isle of Wight and analysed the impact of five specifications:
- Building Standards (Part L, 2021)
- Future Homes Standard (Part L, 2025)
- Technology First, with a heat pump
- Fabric First, with ultra-low energy specs and direct electric
- Comprehensive, with both ultra-low energy specs and a heat pump.
The housing typologies were:
- a small 3-bed semi-detached house
- a small 3-bed terrace house
- a small 2-bed bungalow
- a fairly large 4-bed detached house
- a medium rise block of apartments.
Each was measured against the LETI Climate Energy Design Guidance.
The results are summarised in the table below:
|
Technology First |
Fabric First |
Comprehensive |
|---|---|---|
|
30 kWh/m2/yr |
15 kWh/m2/yr |
15 kWh/m2/yr |
|
Double glazing |
Triple glazing |
Triple glazing |
|
<3 |
<0.6 |
<0.6 |
|
Heat pump |
Direct electric |
Heat pump |
|
PV panels |
PV panels |
PV panels |
Five different ‘specifications’ were modelled for each housing typology: Part L 2021, Future Homes Standard and three different approaches to energy efficiency and net zero energy balance.
Lessons learned
Our findings were that only the comprehensive solution met the LETI requirements. Introducing an ultra low energy-fabric, heat pump and PV panels achieves an energy balance - a balance between the total energy the building uses with the amount of renewable energy generated each year.
The resulting benefits are:
- An ultra-low level of space heating demand in line with the recommendations of the Climate Change Committee, (15-20 kWh/m2/yr), except in the case of the bungalow.
- A fossil fuel free and efficient heating system (heat pump).
- A total energy use compliant with the LETI definition of Net Zero carbon in operation (less than 35 kWh/m2/yr), except in the case of the bungalow.
- An energy balance with roof-mounted PVs for all typologies.
- The lowest energy bills for the residents.
We also provided a set of Key Performance Indicators (KPIs) to target best practice and signify if a building is truly achieving Net Zero Carbon. These targets are recommended over carbon reductions targets.
The costs
We can only achieve these energy efficiency levels if development is still viable.
We calculated the costs for each building typology, fabric standard and heating technology, based on Currie and Brown’s database of energy and carbon saving costs in construction, combined with baseline construction costs.
Our findings were that the cost uplift compared with Part L (2021) and Part L (2025) is estimated at about 5 to 8 per cent. These need to be seen in the light of other changes and costs affecting the housing market. We also see this as a premium which will reduce over the next 30 years as net zero becomes the norm.
We compared these with the Isle of Wight’s viability work in the local plan viability studies. In general, our modelling is consistent, although the four bedroom house is larger and our costing is more granular.
The capital cost of the medium rise block is the highest due to a higher base cost of building, but the uplift for reaching net zero carbon is less than most of the other typologies.
For the smaller buildings, a high form factor results in higher uplift costs for reaching net zero carbon.
The uplift for the fabric first option is generally less than for the technology first option. Sometimes the uplift cost of the comprehensive scenario is not the most expensive (bungalow), this is a result of the reduced costs of PV and of internal heat distribution and emitters in these homes.
The results are summarised in the table below:
|
Cost uplifts/m2 GIA |
Semi-detached |
Mid terrace |
Bungalow |
Detached |
Medium-rise flat |
|
Fabric |
£74 |
£63 |
£101 |
£83 |
£53 |
|
System (heating & hot water) |
£27 |
£25 |
£25 |
£33 |
£27 |
|
PV |
£1 |
£1 |
-£12 |
-£4 |
£8 |
|
% cost increase relative to Part L |
8% |
7% |
8% |
7% |
5% |
How we measure energy efficiency
Energy efficiency, government targets and compliance with building regulations are usually based on the Energy Performance Certificate (EPC) based on the Standard Assessment Procedure (SAP). SAP was originally designed with one key objective - to represent a standardised fuel cost to achieve comfort under given conditions, not for predicting future energy use or other energy efficiencies. We found that SAP underestimates space heating demand by more than 50 per cent in some typologies, so that it under estimates the potential benefits of measures to reduce space heating demand (e.g. better U-values, triple-glazed windows, more airtight dwellings). If the use of SAP is allowed to demonstrate compliance with Net Zero policies, it is recommended that its outputs are corrected to better represent likely future energy use.
We recommend using the Passive House Planning Package (PHPP). The PHPP methodology and tool have been shown to predict energy use much more accurately.
The Isle of Wight could mandate, or at least encourage, the use of PHPP on residential new build projects or alternative accurate methodologies, e.g., Dynamic Simulation Modelling combined with calculations compliant with CIBSE TM54.
We also recommend energy performance measures for airtightness, heat transfer coefficient (HTC) and energy use.
The solution
Our conclusions recommend the comprehensive specifications – the only option which meets the LETI standards:
- ultra-low energy fabric
- best practice air tightness <0.6
- high efficiency MVHR
- heat pump
- PV panels
- low embodied carbon design.
On the information we have at present, these could be achieved without risking viability.
How is the new approach being sustained?
Meeting our targets for reducing carbon and avoiding environmental catastrophe requires real change in both our existing homes and in building new homes.
The purpose of the study was to understand whether a policy of requiring higher environmental standards in our local plan, up to the standard of net zero carbon, would still allow development to be delivered on the Isle of Wight, an Island where there are already challenges to development.
The research concluded that the additional costs of delivering the comprehensive model of sustainable design could potentially be achieved while still maintaining viability.
We will need to carry out further work to assess the impact of developments in the wider economy, in terms of land values, property prices and the costs of supply chains to understand viability. Equally, the costs of sustainable solutions may well reduce over time as they become more prevalent.
The council is testing the response to genuinely sustainable development through its Housing Forum and is considering next steps towards implementing the recommendations in this report in its planning policy, continuing to work in partnership with housing associations on the island.