BIODIVERSITY
Operationalising BNG within NHS estates
Amy Norman, senior civil engineer, Charles Rothnie, senior structural engineer, and Ben Gillham, graduate structural engineer, from civil and structural engineering consultancy Perega, discuss the challenges that the 10 per cent Biodiversity Net Gain (BNG) mandate has had when it comes to operationalising ecological thinking within the constraints of developing existing healthcare estates.
The 10 per cent Biodiversity Net Gain (BNG) mandate came into force in February 2024,1
marking
a fundamental shift in how healthcare infrastructure projects must be designed and delivered. For NHS trusts managing complex, live estates, we are now firmly in the implementation phase. The question is no longer whether to integrate ecological uplift, but how to operationalise it within the physical and budgetary constraints of existing hospital sites. This transition presents what we might call the
‘Brownfield Paradox’. The very structural interventions required to deliver nature-based solutions on constrained urban sites can risk increasing a project’s embodied carbon footprint. Green roofs require stronger frames. Sustainable Drainage System (SuDS) features demand careful ground engineering. Biodiversity zones require access routes for maintenance. Every ecological enhancement can create a cascade of structural implications that must be balanced against the carbon cost of implementing and maintaining the supporting infrastructure. The solution lies in treating BNG as a strategic engineering consideration from day one of the master planning period, rather than a regulatory box- ticking exercise bolted on during the detailed design stage.
The challenge of restricted footprints Delivering a 10 per cent biodiversity gain on a busy hospital site presents fundamentally different challenges to more typical greenfield developments. Space is at a premium. Usually, every square metre of ground-level estate is already committed to circulation, servicing, emergency access or temporary clinical accommodation. This spatial constraint forces estate managers to look upwards and outwards, exploring opportunities in vertical spaces and external works. Rooftop solutions appear attractive in principle.
However, the reality is more complex. Essential plant rooms, lift overruns, emergency helicopter access, and maintenance zones all compete for roof space. This competition for rooftop real estate makes the integration of green or brown roofs a complex planning exercise requiring careful prioritisation of competing operational demands. When green or brown roofs are technically feasible,
they introduce significant dead loads that the existing structural frame may not have been designed to accommodate. There is a considerable payback time for a green roof’s production and maintenance, and
September 2026 Health Estate Journal 65
the economic case must also account for the increased material usage in the supporting structure: thicker slabs, larger columns, additional reinforcement. The carbon penalty can be substantial. This is where strategic load path management becomes essential. Rather than treating every roof area as equally viable, engineers must identify zones where the existing structural grid offers inherent capacity. Locating biodiversity features over shorter structural bays or areas with existing stiffness minimises the need for high-embodied-carbon strengthening works.
The technical nuances of external works External works represent some of the most cost-effective opportunities for BNG delivery on healthcare sites, but they demand careful technical consideration at the master- planning stage. Sustainable drainage systems offer perhaps the clearest win. Swales, detention ponds, and rain gardens can be cost-neutral or even cost-negative compared to traditional buried tank solutions, while delivering measurable ecological benefits. The key is early integration into the site layout. A swale designed into the landscape from the outset becomes an attractive, biodiverse feature. The same intervention retrofitted into a constrained site becomes an expensive engineering challenge. Understanding site hydrology is crucial. Surface water flow paths and infiltration characteristics need to be mapped before the building footprint is fixed. This allows
Outdated hospital buildings at Chase Farm Hospital in Enfield have have been replaced with a new build hospital.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136
