Let’s consider a hypothetical development in an area where BNG is a requirement of a planning submission. This must be considered as now more than an example as every site will be different and it is strongly advised that you speak to us at the earliest opportunity to ensure your site can be assessed and evaluated before you commit to purchasing it, or if you already own it, before you pay for an architect to design a layout. 

Remember that BNG requires a 10% increase in both habitat areas and 10% increase in linear features (swales / hedgerows etc).

We are finding that the maximum hard surfacing on a typical modified grassland (poor semi-improved grass field), is around 45% - in English, this means that the maximum coverage of units, roads, paths and other hard surfacing areas must not exceed 45% of the land available – less than half the site can be built on. 

The percentage will vary depending on the baseline biodiversity value of the site, pre-development. Clearly, areas which consist of existing hard surfacing: roads, car parks, factory units etc will have a very low starting value, making it possible to develop a larger area than a site which is rich in biodiversity. It is also probable that some areas of a large site will be of greater BNG value than other areas, so selecting the best layout will be essential.

Whatever the development footprint, the remaining areas must be used to create a 10% BNG – effectively 110% of the whole initial site baseline value must be condensed into the remaining areas. The smaller the area, clearly the less feasible this becomes.

If we assume the total red line area to be 1 hectare (10,000m2), and sticking to our hypothetical example, the maximum developable area is 4,500m2. 

Assuming the initial Biodiversity Baseline Assessment records 40 Habitat Units and 20 Hedgerow Units, it will be necessary to have 44 Habitat Units and 22 Hedgerow Units post-development. Presuming that the Habitat Units are evenly spread throughout the site, 18 Habitat Units will be lost if 4,500m2 is built on. This means that the remaining undeveloped area (5,500m2) must achieve the BNG.

Consequently, the difficulty now is that the reduced area of 5,500m2 must generate 44 Habitat Units and 22 Hedgerow Units.

This is achieved by creating, or enhancing habitats on site, so that the value of any given area is higher post development than it was pre-development. Clearly the larger the development area, the more difficult it becomes to achieve any gain, let alone a 10% BNG.
Consequently, developers will need to pay far less for development land (or charge significantly more for property), if they can only build on a smaller area of land than was previously presumed and factored into the financials.

Where developers are taking forward sites purchased in the past, the financial viability of these sites is now being questioned. This is especially true for social housing sites, which are borderline viable in many cases, even without BNG. It is also more difficult to create onsite habitats on smaller sites, as the human pressure is simply too great to enable biodiversity to exist alongside children playing football and dogs being exercised. 

Smoke and Mirrors
As with all data / metric based systems, garbage in = garbage out. There are already a number of companies undervaluing existing site biodiversity value.

There are a number of reasons for a distorted result:
1. The ecologist undertaking the baseline assessment has inadvertently mistaken one habitat, or perhaps mis-calculated a habitats value. This results in the baseline metric score being lower than it should be.

This can be attributed to perhaps two genuine causations:
o There is often some professional judgement in assessing habitats and even two knowledgeable people might disagree.
o The ecologist making the assessment lacks experience, or sufficient knowledge to undertake the baseline assessment.

2. The ecologist or company deliberately downgrades the existing habitats and deliberately inflates the post-development BNG to make a proposal appear better on paper, than in reality. 

The first category requires additional training and guidance, whilst the second are simply snake oil salespeople who unfortunately exist in every industry. Incidentally, if the thought crosses your mind that damaging the development site prior to instructing an ecologist might ‘de-value’ the biodiversity value, and make it easier to provide a paper BNG, be aware that Google Earth Pro offers the option of searching for site images over extended periods of time and LPAs such as Cornwall / Dorset will assume a site value commensurate with the highest possible pre-development biodiversity value based on aerial images, which might well be higher than the actual value. 

We are known for our pragmatic (rather than obstructive approach), to development and will assist you in negotiating the increasingly more complex ecological and biodiversity requirements in bring your proposals forward, albeit on occasion there may not be a solution or at least one that accords with the financial considerations of any given site - However, we strongly advise against pre-emptive site clearance and will not work with developers who engage in such practices.