Trees and development guidelines
The visual contribution of trees to the built environment has long been recognised. In addition, trees provide important habitats for wildlife, help to improve air quality, reduce rain water run-off, provide shelter and are integral to the character of the Dorset countryside.
Trees have a significant role to play in achieving sustainable development and the successful integration of trees into a new development scheme depends on the retention of appropriate trees, informed layout design and careful implementation. As part of this process it is necessary to consider the value of the trees within the context of the existing landscape character.
The most important part of a tree, its roots, are hidden. Most tree roots occur within the top 600mm of soil, extending radically for distances frequently in excess of tree height. Damaging tree roots may kill or weaken the tree and, in some instances, may cause the tree to fall. Tree roots require oxygen to survive. Compaction caused by vehicles can asphyxiate tree roots.
The 3 most important aspects of tree protection on developments sites are:
- deciding which trees to retain and which trees to remove
- determining sustainable tree/building separations
- protecting trees effectively during the construction process
Irreparable damage can occur in the first few days of a contractor's occupation of a site. The early erection of protective fencing and ground protection to form the construction exclusion zone, before works commence, is essential to prevent damage.
Planning applications and trees
Trees may occupy a substantial part of a development site and can have a major influence on the planning process and end use. Existing trees of good quality and of appropriate species can add to the quality of a development, and increase its value.
It is important to identify these trees early in the planning process and to successfully incorporate them into the new environment. Poorly sited buildings often lead to the damage or premature removal of such trees. Where appropriate Tree Preservation Orders (TPOs) will be made to ensure that significant trees which have amenity value are retained.
The retention of inappropriate trees imposes unnecessary restrictions on the site and should be avoided. Such trees are unlikely to be retained by future occupiers. Trees may, on occasion, preclude development of land. However, in most cases they can, with careful planning, be successfully integrated into new development schemes.
Securing the services of an Arboricultural Association registered Arboricultural Consultant will smooth the process. In many cases enable the planning application to be determined more quickly.
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Trees and development British Standard process
The following table outlines the requirements of the British Standard. Prospective developers should obtain a copy of the standards publication from the British Standards Institute. You may need to look at the Standards document to make sense of table.
|1. Land Survey
An accurately measured topographical survey to scale showing all trees present on a scaled plan. Trees on adjacent sites should also be shown which are within a distance equal to one times their stem diameter.
The land survey should include locations of all trees, shrubs and hedges, other relevant features such as stems and buildings, and spot level heights.
|2. Tree Survey
||Survey information should include: ref number, species, height, stem diameter, branch spread at four cardinal points, crown clearance height, age class, condition, management recommendations, life expectancy, and British Standard (BS) categorisation. Details of Tree Preservation Orders, Conservation Areas, Planning Conditions.
|3. Tree Constraints Plan
||The influence that trees have on site layout is plotted. This includes the below ground constraints posed by the Root Protection Area (RPA), and the above ground constraints posed by size, position,and future growth potential. protected areas are calculated from the information collected from the tree survey - see BS 587 Table.
|4. Initial Design
The initial design of the site should include locations of: Roadways and sewers, Building footprints (outline including patios, paths etc.) Drains, Hard Surfacing.
Details should also be included of the depth and width of any excavations and level changes necessary to implement the above.
|5. Negotiation (prior to application)
Once the initial design has been received the Council's Tree Officer will examine the tree information, building design and footprints, to ensure they comply with good practice and the relevant British Standards . In an ideal situation the information provided will be acceptable, in other cases changes may be recommended, or additional information required. The Tree Officer will seek to reach a negotiated design solution wherever possible, although in some circumstances significant trees may constrain design.
|6. Tree Protection and/or Removal
Refer to the BS categorisation ( A/B/C, or R). Remember that there may be a legal obligation to retain certain trees, including the replacement of dead and/or dying trees in classes C or R. Particular care and attention should be given to veteran and aged trees.
|7. Design (application submitted)
BS 587 recognises that Protected Areas are not completely 'no go' areas, and that exceptionally it is possible to construct Roadways, Sewers and Buildings within Protected Areas. This is, however likely to be complicated and, without a tree-friendly and informed builder, has great potential to go wrong and damage the trees concerned. Appropriate engineering solutions may include:
Roadways: Geotextile membrane on existing ground level, building up with stone and permeable surfacing. Sewers: install by trench less techniques Buildings: Pile and beam or raft type foundations (see NHBC Standards Chapter). Bespoke building design to minimize potential loss of light.
|8. Planning Approval and Conditions
Once the development has been approved, construction may begin once planning conditions have been satisfied. Various Tree Conditions may be applicable and may include the need to erect protective fencing and ground protection. There may also be a requirement to submit a Method Statement detailing a methodology for operations such as constructing a driveway beneath a tree, phasing of construction works, or pile and beam foundations.
In most cases a pre-commencement site visit will be required where details of working procedures in respect of tree protection will be finalised.
Tree information accompanying planning applications should substantially follow the format of British Standard (BS587, 005). Planning applications submitted which do not conform to this Standard may be rejected as insufficient to be able to determine the application.
Potential damage to structures
Check British Standard S 587 Table to ensure that structures are not likely to be damaged by retained or newly planted trees.
Future building use
The end use of the building will have an effect on the long term viability of retaining such trees, e.g. a large tree on the southern side of a dwelling frontage may cause unreasonable shading and over-dominance.
It is vital to allow sufficient separation between buildings and mature trees to prevent over dominance and apprehension, as this may lead on to pressure to fell trees.
Statutory tree protection
All trees, regardless of their protected status, are a material consideration in a planning application, and consequently the local planning authority will need to consider them.
Local authorities have a statutory duty to make TPOs when considering planning applications. TPOs may be made either to prevent the removal of significant trees, or to protect significant trees from damage. Trees with TPOs require consent from the Local Authority before they can be pruned or removed.
All trees within conservation areas which have a stem diameter of at least 7.5 cm are automatically protected, and pruning or removal requires the consent of the council.
Current and future tree size
Existing and ultimate crown spreads should be considered. This information will assist in designing the development to accommodate retained trees not just at the time of development completion, but also for when the tree reaches it's mature size.
Tree information required
On sites where trees may be affected by development a Tree Survey, Impact Assessment and Method Statement is likely to assist the local planning authority in determining the application.
As well as construction details the Method Statement should refer to temporary features such as details of vehicular access for construction traffic, areas for material storage, site huts, etc. as well as details of protective fencing and any other methods to be used for protecting trees both during and after the development.
Temporary access through Root Protection Areas may be achieved using appropriate ground protection and fencing.
Tree felling and surgery
It is preferable to undertake any approved felling or surgery prior to commencement of building operations once planning approval has been granted. All such works should conform to British Standard BS 998.
Tree planting and landscaping
Landscaping and replacement planting is sometimes required. It is useful to have detailed plans submitted as part of the Design Statement.
Allowing sufficient space for new trees will inform and compliment the design process. Car parks and open spaces often provide excellent opportunities for tree planting.