Gilston Garden Town

Our response to the outline planning application 3/19/1045/OUT

“We consider the Council needs to refuse outline planning permission to Places for People in relation to their outline plans for the Gilston Estate as it does not meet EHDC’s recent climate change motion: to do everything within the authority’s power to reduce its impact on the climate and moreover do everything we can in supporting the whole of East Herts District to become carbon neutral by 2030.

We have demonstrated to the Council that they can and should require developers to deliver developments which in use are from the outset net zero carbon. The detail of this is set out in the draft Supplementary Planning Document which we have provided to Councillors and the Head of Planning.

In this application for Gilston, the developer has included an Environment Statement which in chapter 20 suggests that on a whole life cost basis the development’s carbon emissions in use and the carbon emissions embodied in the buildings on the site would be “carbon neutral” after 51 years due to the carbon sink across the development and the rest of the site. The whole life approach to carbon emissions assessment in the Environmental Statement (ES) is an interesting development, going beyond the approach we have proposed in the SPD. But we consider it to be flawed, as set out in the Appendix below.  Even on its own terms we assume the developer is arguing that it will have achieved carbon neutrality in 2071 – certainly not by EHDC’s target date of 2030!

In direct comparison with the net carbon zero approach we advocate, the outline planning application proposes to achieve 19% less CO2 emissions than the baseline level that would be achieved by full compliance with the Building Regulations, equivalent to meeting the carbon emission requirements of the abandoned Code for Sustainable Homes Level 4 rating. The Environment Statement calculates that this equates to residual emissions of some 9,459 tonnes of CO2 per year. This is the cost of not taking further action to reduce the buildings’ emissions to zero.

The embodied carbon emissions in the development are the carbon emissions associated with the building materials and methods used in construction. In the Environment Strategy the academic author notes that the building industry has committed to reduce embodied carbon, as measured by carbon intensity of the buildings, by 48% by 2030. She identifies many opportunities for this in Table 20.13. The Gilston developer is committed in its Sustainable Development Strategy to  “work towards eliminating avoidable waste in construction and design, and support moves towards a circular economy” but this does not include a measurable commitment to reducing the carbon intensity of the buildings for the site. 

The developer’s water efficiency proposals are not ambitious, set at 110 litres/person/day, despite noting the importance of this in an area of water stress. Water use is not only important to avoid adding too much more stress to the aquifer, but also because of the energy used in the water processing and distribution system. The now archived Code for Sustainable Homes considered it possible to design homes to achieve 105 or even 80 litres/person/day. Southern Water, Waterwise and the Environment Agency support a target of 100 litres per person per day by 2040. Although this is not a requirement, the failure to aim for this shows little commitment to sustainability.

The outline planning application envisages achieving its target of 19% less CO2 than the baseline, by building homes to high energy efficiency standards and using solar PV or solar water heating. It envisages each home having a gas boiler for space heating, because the energy efficiency expectations are not sufficient to rule out the need for heating. This contrasts with Passiv Haus standards which reduce heating requirements to such a level that gas heating systems are not required.

The energy strategy rules out district heating on grounds that the amount of heating required across the site is insufficient to make it commercial. It is not clear whether this analysis is based solely on domestic heat requirements and whether it has factored in other heat/cooling requirements from commercial buildings which could alter the calculations. It is also not clear whether it considered the potential for the heat system to be used by existing buildings/businesses in the adjacent area and whether it could draw on heat from existing industrial or renewable sources nearby. The District Heating assessment appears to have been based on gas combined heat and power and savings calculated over 20 years, with relatively low grid factors in the calculation. It appears not to have taken into account the Government HNIP funding for heat networks which is now available (and wasn’t available in 2016/7 when we believe the heat networks analysis was undertaken). The HNIP funding is designed to increase the viability of heat networks to achieve the IRR/hurdle rate to make them viable.

The timing for the build out of Gilston Estate is over 20 years to around 2040 and its future proofing approach is that the developer promises to use its reasonable endeavours to adopt new best practice as it emerges. The Government has made a commitment that from 2025 at the latest, no new homes should be connected to the gas grid. The planning documents for Gilston note that the energy requirements in the Building Regulations are currently under review and suggest that the proposed energy strategy is designed to be flexible, allowing the developers to use their “reasonable endeavours” to consider and introduce alternative technology for later phases.  EHDC should future proof its current planning approvals by not building in new extensions of the gas grid in advance of gas no longer being allowed – this would save developers’ costs; and should ensure it is not only relying on the developers’ “reasonable endeavours” to use the best available technology.”

Technical comments on the Environmental Statement, volume 1, chapter 20


The whole life approach to carbon emissions assessment in the Environmental Statement (ES) is an interesting development and, in principle, appears a good way to proceed. But the Environment Statement does not give full transparency to the calculations involved, includes implausible and unsubstantiated numbers and does not give proper consideration to the opportunity cost of losing the sink capability from the land in alternative use to agriculture.


The whole life approach to carbon emissions assessment in the Environmental Statement (ES) is an interesting development and, in principle, appears a good way to proceed. It is stated that this assessment approach has been used for other major regeneration schemes within the UK but is only currently undergoing verification at the Carbon Trust. So, we assume that as of now it has no external validation.


Carbon sink

There is a fundamental issue with the distinction here between a carbon sink and carbon sequestration. The quoted paper Edmonson (2014) discusses soil organic content (SOC) at the time of measurement and does not make any suggestion that the SOC figures can be scaled to increase with time. There is no mention of a study period of 25 years. Furthermore, it seems reasonable to assume that the SOC for the many woodland areas within the Gilston development area would have reached close to a steady-state condition as they are described as Ancient Semi-Natural Woodland (ASNW) in the comments on this application submitted by the Woodland Trust. This steady-state condition for woodland carbon sequestration is illustrated in the Natural England (2012) report Figure 1, cited as ES reference 33. The scaling of SOC for 60 years mentioned in 20.3.15 therefore appears invalid for many of the existing landscapes.

Carbon sequestration

This is treated as a separate process from the carbon sink, but it is unclear where the sequestered carbon finally becomes captured. If the sequestered carbon is not stored within the carbon sink then it is unclear whether it remains captured or is subsequently released. It seems reasonable to assume that the rate of increase of carbon in the carbon sink cannot be greater than the rate at which it is sequestered from the atmosphere through photosynthesis.


The ES proposes an embodied carbon intensity of 781 kg CO­2/m2 for 50% of the floor area and 405 kg CO­2/m2 for the remaining 50%. The first figure appears reasonable and matches with the data quoted in the 2018 Taylor Wimpey Sustainability report[1], although the Taylor Wimpey figures already include a proportion of timber-frame build.

The second figure for timber-frame buildings of 405 kg CO­2/m2 has been taken from ES reference 30[2] and applies to a ‘novel low energy house’. This is a research proposal, and so it is unclear how this relates to timber-frame building designs of real-life developments. The paper[3] claims that the novel construction method achieves a 34% reduction relative to conventional buildings, rather than the 48% (405 vs. 781) implied by the ES. A key difference is that the figure of 405 kg CO­2/m2 in the research paper does not include scope 3 emissions.

The ES has therefore not provided plausible evidence that the reduced figure of 405 kg CO­2/m2is valid, or that it is achievable within the timescales proposed. There is certainly no commitment within the outline planning application to deliver it.


Appendix 20.2 is cited as quoting numbers of dwellings for use in the carbon assessment. This appears to be the lower table on page 129 of the ES volume 3 file[4]. The table provides numbers of each type of dwelling, but the meaning of further columns labelled ‘Dwelling’, ‘Quantum’ and TER and DER is unclear. These values have no units and there is no explanation as to the method used to combine these figures to derive the total TER used later in the ES.


The requirement for a 48% reduction in carbon emissions due to construction by 2030 is claimed to be met by the adoption of timber-frame build, using the lower figure of 405 kg CO­2/m2 as discussed above. This would imply that 100% of the construction by 2030 can achieve this lower figure. However, the Taylor Wimpey 2018 Sustainability report claims that currently only 10% of buildings use timber-frame and they would ‘aim for 20% by 2020’. It therefore seems improbable that 100% the target would be met by 2030. Notably, the Housing Statement provided with the application makes no mention that 50% of the buildings would have a novel timber-frame construction.


This section quantifies the existing carbon sink of the site in Table 20-9. The table includes soil carbon ‘metrics’ which have no units and no reference. The ES does include reference 31 which provides, for example, soil carbon for arable land of 120 tC/ha. It is unclear how this could be converted to derive the ‘metric’ for arable land of 26.69. In order to calculate the total carbon sink in the third column, it would also be necessary to know the area of each land-use type. This is listed on p129 of Appendix 20.2, but again, there is no explanation of how the total carbon sink for each land-use type is calculated.


This section calculates the annual carbon sequestration. Again, the values in Table 20-10 have no reference, and there are no figures provided for the sequestration per unit area, or the emissions associated with the arable cultivation.

A key point here is that the total annual sequestration is significantly reduced by the large negative factor included for arable land. This allows for the carbon emissions associated with arable cultivation. However, these emissions are not avoided by the development taking place and would be displaced elsewhere. Without this deduction, the annual sequestration for the existing site would be greater than that shown for the development in Table 20-14.


This section makes an unjustified claim that the agricultural practices of the existing site would not change over the next 60 years. However it is completely plausible that cultivation practices will change as the need to preserve soil carbon content becomes more widely recognised, possibly by adopting new practices such as agro-forestry. The need for significantly increased areas of tree-planting has now been identified by the Committee on Climate Change[5].     In response to the UN IPCC report published on 8 August 2019 the NFU has stated its aspiration for UK farming to become carbon neutral by 2040.


Figures are quoted here for residential and non-residential buildings, but there is no explanation as to how these figures are used in the following calculations.


The units here appear incorrect, based on Appendix 20.2m where the savings from PV installations are 8500 dwellings x 166 kgCO2/dwelling/year, giving a total of 1,411,255 kgCO2 /year.

The basis for the figure of 166 kgCO2/dwelling/year in Appendix 20.2 p127 is also not stated. Clearly some dwellings are apartments and so have no dedicated roof area so the use of this pro-rata figure for the PV carbon savings is opaque. A more appropriate method would be to provide the savings from PV per square meter, and then to provide the roof area and number of dwellings to which it can be applied. As it stands, the quoted figure per dwelling provides no further clarity than is given by an un-substantiated total figure and the total number of dwellings.

PV panels typically have a design lifetime of 25 years. The application should therefore commit to maintaining the electricity production from the PV for the life of the development to ensure that the claimed savings can be achieved in practice. This would require further investment of new panels and it cannot be assumed that house owners will do that investment. If they did it would add to the embodied carbon figure for the development.

The carbon savings from ‘Fabric First’ design also appear to have incorrect units (presumably this should be 1,602,000 kgCO2 /year to give the total of 3,013,599 kgCO2 /year as in Table 20-16). Again, there is no explanation of the basis for this additional carbon saving.


No justification is provided for the quoted saving of 30 kgCO2/dwelling/year from the developer’s commitment to reduce water use from 125 litres/person/day to 110 litres/person/day. It is not clear that this would not already be built into the 19% figure for carbon reduction compared to the building regulations.


Again, no justification is provided for the further carbon saving.


ES reference 32 to Waterwise links only to a website and does not appear to provide the quoted figure of 2.2 kgCO2/dwelling. However, the Energy Saving Trust[6] recommend a figure of 0.75 kg/m3, which would correspond to 95.8 kgCO2/dwelling/year if the dwelling uses 350 litres per day, a figure much higher than appears in the ES.


The quoted total carbon saving for water use of 1,241,000 kgCO2/year is not substantiated by any calculations. If there are 8500 dwellings, that would be a saving of 146 kgCO2/dwelling/year, a figure much higher than the proposed savings of 30 kgCO2/dwelling/year in sections 20.6.12 and 20.6.13.


This section presents the carbon sequestration of the proposed development. The rates for the existing land-use types, such as the woodland, appear to be scaled in proportion to the area that would remain. As before, there is a negative sequestration for the arable land due to the carbon emissions associated with farming. However, the ES does not appear to apply a consistent approach for parks or gardens as there is no mention of carbon emissions associated with landscape maintenance.


This quotes a total TER of 15,617,402 kgCO2/year for the development. There is no justification provided for this figure, and it is unclear how it could be derived from the TER and DER figures listed in Appendix 20.2 on p127.


Contrary to the comments in this paragraph, Appendix 20.2 does not provide any justification for the figures in Table 20-17. The areas are listed for the Stort crossings on p129 but no detail is provided for the embodied carbon.


The figures for the carbon sink of the proposed development are summarised in Table 20-18 and listed in further detail in Appendix 20.2 p129-p130. As with the figures for the existing development, a ‘metric’ is listed for each land-use type but with no units or explanation to show how this can be multiplied by the appropriate area to reach the 25-year total.

The ‘metrics’ are the same as those used for the existing development. However, the figures provided by Edmonson (2014) for closed surfaces (e.g. roads and the built area) do not confirm that these areas will act as a carbon sink. The paper states “As yet it is unclear whether the OC stocks in soils beneath impervious surfaces are essentially passive, and therefore a reflection of the OC present at the time of capping, or whether there is active turnover of OC in the soils”. The examples quoted in the paper are described as “patches of patio, garden path or residential driveway” where root growth is likely to occur from adjacent green-space. The paper does not conclude that carbon is actively captured underneath wide areas of paved or grey infrastructure.

The carbon sink value for the natural green space is shown in Appendix 20.2 as 80,105,111 kgCO2 after 25 years. This is implausibly high in comparison with the existing ASNW woodland which has a similar carbon sink value of 87,851,988 kgCO2 after 25 years, especially as the natural green space is said to have only 20% woodland cover. The carbon sequestration rate for the natural green space is listed in Table 20-14 as 110,762 kgCO2/year, giving only 2,769,050 kgCO2 after 25 years so it is unclear how the high carbon sink value has been created.


The ES claims that carbon neutrality can be achieved after 51 years. There are no calculations provided to substantiate this, and the actual carbon balance would appear to be significantly worse.

Taking the figures provided at face value, there is an embodied carbon cost of 535,671,221 kgCO2 and a total operational carbon cost over the 60-year period of 937,044,120 kgCO2. This operational carbon cost is offset by savings listed in Table 20-20 to reduce it to 567,526,620 kgCO2. The total embodied plus net operational carbon is therefore 535,671,221 + 567,526,620 = 1,103,197,841 kgCO2.

The ES sets out a difference in carbon sinks between the site developed and the site as currently used for agriculture and woodland claiming that the developed site achieves a net increase in carbon storage of 59,023,830 kgCO2. There appears to be no possibility of this balancing with the increase in embodied and operational carbon from the development and so it is unclear how carbon neutrality could be achieved at any time period.