Did you know... planning authorities are now asking for you to accurately plot the location, canopy shape and root protection area (RPA) for all trees that may be affected by new construction and structures that require planning permission?
Did you know... many planning authorities are requiring you to use BS5837:2005 ‘Trees in relation to construction’ as the basis for this assessment?
How does this affect you?
The effect of trees on development and the impact of development on existing trees cannot be ignored. Trees are not just the pretty things that “soften” the appearance of a place but are essential contributors to our comfortable living environment and an aide to construction.
The environmental benefits of trees are well documented. Trees reduce particulate pollutants; provide shade and shelter; provide a living room for wildlife; and, help offset some of the affects of global warming...
What is often overlooked is the contribution trees have made to construction. They reduce building energy use by cooling in the summer (shade) and offer shelter in the winter. Trees can help stabilise banks and loose ground; intercept and slow down rainwater run-off; lock up contaminates in the soil; rebuild soil structure over time through leaf mould and decay and, in some cases, fix nitrogen in the soil.
However, get it wrong and trees can be very destructive. Tree roots can cause soil heave that can destroy surfaces and undermine foundations making them hazardous and dangerous. In shrinkable clay soils, the wrong species in the wrong location can make the soil unstable which may result in subsidence to buildings. Tree roots gravitate to water and can infiltrate and destroy broken drains. Trees can exude excessive dew that marks surfaces and structures and rotting leaves can make surfaces slippery. As trees age, infection, death and decay, if left untreated, can cause serious injury and death to individuals.
Of course, if trees exist on site, the positioning of structures too close to them will contribute to the above problems. Building too close to trees will inevitably require you to excavate into the root zone which is detrimental to the trees short and possibly long term chances of survival. Also, it can force the tree to grow away from the structure making it unstable. Introducing site drainage and changes in site levels through terracing and mounding can significantly affect the local water table, either starving the roots of water or condemning them to waterlogged conditions that can affect the viability of the tree. Even surface choices can have an impact as curbs cut into fibrous surface roots and impermeable surfaces take water away from the tree.
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There is no escaping the fact that if you build vertical or surface structures too close to a tree it will affect its viability. As a designer, selecting the wrong tree species or planting in the wrong location can also have a significant impact on existing surfaces and structures.
The relationship between trees and construction is inextricably linked. As a designer offering professional landscape advice to your client, you have a Duty of Care to advise clients to consult an Arboriculturist where trees exist on site. This duty is also extended to your designs, as the wrong species planted in the wrong location can have significant implications to you and your client in the long term. For this reason, the inclusion of a maintenance schedule is vital to make the client aware of their obligations.
This Standard replaces BS5837:1991 and recognises that there can be problems of development close to existing trees where these are to be retained. It “provides recommendations and guidance on the principles to be applied to achieve a satisfactory juxtaposition of trees, including shrubs, hedges and hedgerows, with structures. It follows, in sequence, the stages of planning and implementing the provisions which are essential to allow development to be integrated with trees.” (Abstract from Trees in relation to construction)
BS5837:2005 Trees in relation to construction is intended to help professions concerned with trees in relation to construction form balanced judgments and assess which trees are worthy for retention. Furthermore, it offers a means of protecting these trees during the development phase, including demolition and construction work, and a means of incorporating trees into the developed landscape.
The process describes what factors should be taken into consideration when preparing your tree report. In essence, it requires you to accurately plot the location of existing trees on site and provides a template to describe them based on species, height and the shape of the canopy, based on North, East, South and West (NESW). Each tree should be assessed and categorised using suggested “quality” criteria. These should be presented as a coloured drawing that references a schedule (table) and included with your tree report.
Where trees are to be retained, you need to calculate and indicate on the tree plan the suggested root protection area (RPA) or root zone. This area should be protected by fencing throughout the contraction phase(s) of the development. Where new developments will impact on existing trees, a shadow analysis may be required.
The preparation of this information can be time consuming and difficult to present. However, KeyTREE can help you prepare plans that comply to BS5837:2005 Trees in relation to construction as it will allow you to:
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Survey
Import tree data from external databases (Excel, Access, Dbase or text-based files) and import tree positions located in Google Earth.
Create and modify trees at their correct location, including drawing the canopy shape based on North, East South and West (NESW) values.
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Assess
Assess and categorise trees based on BS5837:2005. Category colours based on: A = Green, B = Blue, C = Grey, R = Dark Red. Add hatches for presentation purposes.
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Validate
Calculate and plot tree RPA’s base on BS Calculated formula, including percent offset from centre of tree.
Make sure you comply to the BS using our BS Conformance Checker.
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Present
Show tree shadows for any specified location and time of day.
Produce a drawing schedule that can be exported to spread sheets and databases.
Publish your tree data to Google Earth for distribution to your client and other stakeholders.
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For more information please go to Keyscape.co.uk/KeyTREE
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