Briefing note on the implication of the new BS 5837 revision for planning professionals

A full revision of BS 5837: Trees in relation to design, demolition and construction, comes into effect on 30 April 2012. There are some important changes with the potential to significantly impact on planning applications and the management of sites with trees:


Expect a dramatic reduction in the area of hard surfacing allowed in root protection areas (RPAs). Clause 7.4.2.3 states: “New permanent hard surfacing should not exceed 20% of any existing unsurfaced ground within the RPA”, which is a significant move from the previous wording, which stated: “11.3.4: new impermeable surfacing within RPAs should be confined to … an area no greater than 20% of the root protection area…”. The old figure only applied to “impermeable” surfacing, whereas the new wording relates to all “permanent hard surfacing”, which appears to include permeable and impermeable. This is likely to make it much more difficult to install surfacing within RPAs unless planning submissions are accompanied by case studies supporting deviations from the BS recommendations.

Confusion over whether category C trees (low quality) are now a constraint! If local planning authorities (LPAs) strictly adhere to the letter of the new BS, we may see projects being forced to retain low quality trees. The old BS had a clear presumption that poor quality trees (called category C trees as opposed the better category A and B trees) “will usually not be retained where they would impose a significant constraint on development”, which limited the extent to which LPAs could use the existence of poor trees to obstruct development. However, the 2012 revision confuses that position, stating “…relevant constraints should be plotted around each of the category A, B and C trees…” without any qualification that category C trees should not be a material constraint. In the context that category A, B and C trees can often represent the majority of trees on the average development site, LPAs seeking to block development could insist that category A, B and C trees are retained! Other than going to appeal, the only way to counter this will be through robust and qualified expert tree support for planning submissions.

All veteran trees are now to be listed as category A (high quality), which means that there will be a presumption to retain them. Such trees usually have large trunks, which could result in a 15m radius for the biggest trees. Furthermore, it is recommended that “no construction, including the installation of new hard surfacing, occurs within the RPA”. Of course, there are often very good arguments to say that veteran trees require a smaller than normal RPA, but this is a technical issue that would have to be supported by expert analysis.

It is no longer possible to displace RPAs by 20% in any direction for open grown trees, which means the only opportunity to adjust RPAs is now through expert interpretation. This rule has been removed, which means it is no longer possible to adjust RPAs using a simplistic recipe.

Calculations of the RPA will now be more complex and require expert interpretation. The rules for measuring multiple stemmed trees have been expanded, so it is no longer a simple single measurement at ground level. This will require more measurements and a greater degree of interpretation at the time of inspection.

The provisions for site monitoring have been reinforced, so that now all operations within RPAs must be subject to arboricultural supervision.

Soil assessment is now listed as necessary at the feasibility stage, which may come as a surprise to most designers. This would normally be considered as information to assist the preparation of detailed proposals when consent is given, not a necessity to assess feasibility at the early planning stage.


On the face of it, this revision provides a number of opportunities for LPAs to strictly interpret the new provisions as a means of thwarting development. It also strengthens the constraints that trees can impose at the design stage and increases the precautions that developers have to take during construction — all burdens that are likely to reduce the efficiency of processing planning applications and organising construction, which in turn, could significantly reduce the investment potential of projects with trees.

However, the BS Foreword states: “Any user claiming compliance with this British Standard is expected to be able to justify any course of action that deviates from its recommendations”. Of course, this will require expert credentials and robust reasoning, but we are confident that this will provide us with the opportunity to customise an approach to each individual site that will minimise the problems from these changes. Our extensive experience at dealing with complex projects means that we have the evidence and case studies to justify a deviation from a strict interpretation of this Standard, if a feasible alternative exists.

Although this revision will undoubtedly allow LPAs to obstruct what they may see as undesirable development, from our experience, we know that there are practical solutions to most of the problems that could be encountered. One of our core skills is to find creative and innovative solutions to these problems and we are confident that we will be able to apply our interpretations in these difficult areas to your advantage. If you are anxious about how trees may affect your project or you are struggling with an obstructive LPA, then please call or email us to see what we can do to help.

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