Many architects have never heard the words ‘nutrient neutrality’. But practices active in dozens of rural areas across England have seen development control coming to a standstill since March this year because of it.
That is when nutrient neutrality became a requirement of new residential developments in and around designated protected areas. Councils were advised that no new permissions should be granted unless they were satisfied that developments could either secure nutrient neutrality or were exempt.
“Planners were caught totally unawares," states Matt Wood, Head of Housing at Norwich-based Hudson Architects. “At one point, Norwich stopped processing residential applications completely”.
Natural England advised 42 local planning authorities (LPAs) that they were now required to prevent new dwellings from adding wastewater run-off – particularly phosphates and nitrates – that would enter a host of areas.
Proving that a development avoids doing this is, essentially, what nutrient neutrality means. Thirty-two local authorities were already subject to restrictions, bringing the total of LPAs affected to 74.
The advice from Natural England has been reproduced in full by some of the affected authorities, such as Cornwall. It summarises key tools and guidance documents and lists catchment areas and local authorities affected.
What kind of developments are affected?
The need to achieve nutrient neutrality applies to applications where there is a net increase in the number of dwellings, including single dwellings. In general, commercial development, schools, and retail can be exempted, but tourist accommodation cannot.
Within the designated areas, proposals need to be supported by a Habitats Regulation Assessment (HRA), which should either demonstrate neutrality or be accompanied by an appropriate mitigation strategy.
Sites outside catchment area borders, but where the effluent is discharged within the affected catchments (i.e. the location of the site’s sewage outfall), will also need an HRA.
Nutrient calculators and the affected regions
Areas covered include parts of the borders and Cumbria, Teeside & Cleveland, Norfolk, Kent, and much of South West England.
Natural England also unveiled new nutrient calculators, which will make wastewater mitigation strategies more challenging. There is a calculator for each area: one for Solent, one for Itchen, and so on. They are downloadable on the relevant local authority websites.
“We are still waiting for accurate mapping of designated area borders,” Matt Wood observes, “while the pattern here seems to be that councils are writing their own nutrient calculators and guidelines as alternatives to Natural England.”
How are planning applications affected?
The Planning Advisory Service told local authorities it anticipated planning departments pausing the determination of applications and negotiating extensions of time for those already in the system.
Hudson Architects were lucky in that their projects were either too advanced or too early to get caught by the planning impasse.
The most serious problems, Wood points out, are being faced on larger schemes that have outline planning permission but where planners are using the reserved matters planning stage to treat them almost like fresh applications.
It is too late for developers to factor the cost of mitigation measures into land values on such schemes.
How can a project prove its nutrient neutrality?
Strategies can include:
- the establishment of offsite treatment wetlands
- interceptor wetlands (capturing agricultural run-off)
- upgrading of inefficient treatment plants
- on-site measures such as Sustainable Urban Drainage Systems (SuDS)
Danny de la Hey, Principal Ecologist at environmental consultant ECUS, explains that while SuDS will work for some locations, it is not going to be a magic bullet. SuDS/Wetlands require a significant amount of neighbouring land which will not always be available.
At present, de la Hey believes developers are hesitant about investing time and money on SuDS/wetlands without any certainty that schemes will pass the HRA Integrity Test.
Nevertheless, he says new guidance is in preparation that will advise on creating SuDS with increased capacity to remove nutrients. He sees this as a good way forward for schemes where land is available.
Possible solutions for small scale projects
There is specific guidance on phosphorus discharge for very small scale developments that can be regarded as having a de minimus effect. More information on this can be found in Annex F of Natural England’s outline guidance.
Small discharges using small scale sewer systems, which go to the ground and produce less than 2m3/day can be deemed acceptable as long as certain criteria are met. These sites would also need to meet the Environment Agency’s general binding rules.
This route, de la Hey reports, has been successful for some smaller developments in Somerset, which has produced its own Interim guidelines on small scale thresholds based on national guidelines.
Long term solutions
In the longer term, de la Hey suspects that local authority-led mitigation schemes will emerge as important local solutions. There are several nutrient trading platforms in development that will allow developers to purchase credits offsetting nutrient loading. But such schemes take time to develop.
In the meantime, there may be ways forward for some sites. One might be taking agricultural land out of production, and upgrading small scale sewage treatment systems to provide betterment. Ecus has provided advice on several bespoke nutrient mitigation schemes.
Who should compile the HRA and mitigation schemes?
Assembling HRAs alongside proven mitigation schemes is, in practice, going to be beyond the capacity of most architects.
Environmental consultants and ecologists who specialise in nutrient neutrality are best placed to assist until national and local measures are clearly defined. Early engagement with environmental consultants, and consultation with the LPA, could provide suitable mitigation strategies at the design stage.
Thanks to Matt Wood, Head of Housing, Hudson Architects; Danny de la Hey, Principal Ecologist, ECUS.
Text by Neal Morris. This is a Professional Feature edited by the RIBA Practice team. Send us your feedback and ideas.
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