Specific issues, which will require consideration in site design and layout include:
British Standard BS5837: 2005 makes reference to the need for a tree constraints plan (TCP), which is a design tool which should show the below and above ground constraints posed by the trees, and the benefits of an arboriculture implications assessment.
During construction works the roots of the tree can be particularly vulnerable. The lateral extent of a tree's roots can vary widely and be irregular. However, as a rule of thumb, the roots of most trees spread to the outer limit of the tree's crown, or slightly beyond.
For tall columnar trees (such as Lombardy poplars), it is reasonable to assume that the roots spread out from the tree for a distance equivalent to about half the height of the tree.
Almost all of the roots will be spread out laterally, like a shallow underground plate, within the first 600mm of soil under the tree. The majority of roots are typically less than 0.5mm in diameter. They are fine strands, vulnerable to damage by cutting (eg when digging foundations, or stripping topsoil), compaction (eg by storing heavy materials or equipment or soil on the ground above) or by poison (eg by diesel or cement).
If foundations and other trenches have to be dug under a tree's canopy, roots are likely to be severed. Where trees are near to a proposed building, developers might volunteer to use "pile and raft" foundations. Piles are inserted through the root plate at regular intervals, and the raft (or slab) sits on the piles. Fewer roots will be severed, but other roots may be damaged by the weight of the pile driving machinery. The fact that a developer is proposing to use the "pile and raft" method may suggest that the building will, in the long-term, be too close to the tree.
The construction of driveways and hardstandings can also damage roots. The foundations for a driveway typically go down 300mm, ie half the depth of the 600mm root plate. There is a "no dig" method of driveway construction (described in Arboricultural Practice Note 12 of the Arboricultural Advisory and Information Service). Geo-grid membranes are spread beneath the tree to support the weight of a permeable hard surface. The success of this method depends upon the amount of root area that would be covered, and the health and vigour of the tree.
Table 2 in BS 5837:2005 sets out the formula for calculating the necessary root protection area (RPA) around trees during development. If fencing cannot be erected in accordance with the guidance, because the building works would need to come too close, then it is likely the tree would suffer long term harm. We will therefore normally allow a reasonable margin for error. The good intentions of a developer cannot protect a tree from an errant digger driver. The distances given in the table are intended to provide a guide for the protection of trees during building works. They are not, as frequently suggested, a guide to the minimum distances within which building may safely take place near to trees. A fully mature tree may die if it loses 10% of its roots.
Above the ground, trunks and branches are also vulnerable to damage, mainly as a result of collision from mechanical equipment, or the erection of scaffolding. This is particularly the case if a site is cramped, and there is little room for manoeuvre.
In the light of the above information it should be possible to determine whether or not the construction works could be carried out without undue harm to the tree.
Applicants should include a full survey to BS 5837:2005 and identify in their proposals the extent of the RPA and include in their planning application Failure to do this will result in the application not being validated and registered.
The application should include proposals for secure fencing during construction. Within the protected areas there must be no storage of any materials (including soil) or ground movement. This will normally be re-inforced by planning conditions.
Even if a tree survives the construction phase, the proximity of the development could, over time, stunt the tree's growth by depriving it of light or water. The tree could then die back, or develop an unbalanced shape. Alternatively it could overshadow an adjoining building or garden area or cause damage to the property through root growth or movement of the crown in high winds. Even if the tree is protected (eg by a TPO, or by its presence in a conservation area) its proximity to the development may nevertheless make it difficult for the Council to resist subsequent applications to fell or prune the tree on safety grounds.
Trees that are not fully mature at the time of the development, will continue to grow. Tree roots will continue to spread outwards. Development that was not previously affected by the trees might then become vulnerable to damage. Trees that overhang or are adjacent to a development can cause dampness, their leaves can block gutters and their roots can interfere with foundations and underground services. Such potential problems may indicate that planning permission should be withheld if tree growth is likely to cause such unsatisfactory relationships.
If the site's sub-soil is a shrinkable clay, the take-up of moisture by trees during periods of drought can cause subsidence and damage to foundations. If the tree has to be felled at a later date, the ground may subsequently swell or heave, as moisture returns to the sub-strata, causing damage to foundations once again. Accordingly, conditions may be necessary to require foundations to take account of tree growth or loss. This is acceptable in order to achieve a defined planning objective, even though building regulations may (or may not) provide parallel control.
Trees can cause emotions to run high. A large tree can be frightening, particularly when it sways. Trees can produce poisonous fruit and berries. Birds roosting in the trees can be noisy and messy. Trees can make gardens damp and dark, and prevent garden plants from growing. Debris, such as leaves, needles, cones, pollen and honeydew, falls from trees throughout the year. This can be perceived as a nuisance. Trees can make living conditions inside a dwelling dark and claustrophobic. Occupants may also find it difficult, or even impossible, to insure their premises if they are too close to large mature trees.
Any of these problems will, in all probability, result in subsequent pressure from the owners/occupants of the building to fell the offending tree(s). The Council may withhold permission for development if they consider it probable that such problems would arise in future.
We have regard to the fact that what we see at the site visit represents only a snapshot in time. Most trees will continue to grow. Consideration should therefore be given to what they may look like in decades to come.
The visual impact of losing a tree has to be weighed against the visual benefits of any new trees planted as part of a landscaping scheme. Landscaping schemes for residential developments seldom include trees that will grow to any great stature. Furthermore, it can be 10-15 years before a new tree makes any kind of a visual impact.
Consideration of all the matters referred to above help in weighing the balance of the evidence. As always, applicants will put forward many arguments in support of their proposal.
The following are some of the most common:
a. "The tree is past its best. It would be better to fell it now, and replace it with one or more new ones,"
Trees do not live forever, but the premature felling of a mature tree is hard to justify. New replacement trees are typically planted at about 2-3m high, and take about 10-15 years to make a visual impact.
Larger replacement trees, several metres high, can make an instant impact, but they are expensive to plant and require timeconsuming aftercare. There would also need to be ample manoeuvring space within the site for the necessary lifting equipment.
Consideration will also need to be given as to whether there is sufficient space within the proposed development for suitable replacement trees to grow to full maturity. Replacing a mature oak with an ornamental cherry is unlikely to make the same contribution to the character of the area.
b. "In due course, the tree will have to be felled anyway, because it is dangerous. Bits are falling off it."
It is natural for dead wood to fall from trees. Regular cleaning out of the tree's crown by a tree surgeon can prevent the unexpected fall of dead wood.
c. "There are lots of other trees in this area; one less won't make any difference"
This is an argument that can be repeated too often.
d. "This is a forest tree. It is not suitable for a domestic garden. It should be felled, to make way for the proposed extension, and be replaced by something more appropriate"
Which came first; the tree, or the house and its occupants? Prospective house purchasers may be unaware of a tree when deciding to buy a house, failing to appreciate the implications of living next to a large tree, until it is too late. This does not necessarily mean that it is acceptable to remove the tree.
e. "The tree could be pruned to keep it away from the proposed development"
Pruning can make matters worse. New growth will be rapid, and the tree will need regular pruning year after year, and be weak at the point where new growth joins old branches. Unless skilfully done, pruning can result in an unbalanced canopy which, in turn, can destabilise a tree.
(The notes above are based on advice given to Planning Inspectors in considering appeals)
Once a potential site has been identified for a development, it is recommended that contact be made with the Local Planning Authority in order to assess any constraints on the land. With specific reference to trees, clarification can be sought on Tree Protection Orders and any other legal constraints. Advice can also be provided on the likely requirements of a planning submission. Depending on the advice given, the following surveys may be necessary. The necessity for surveys will depend on the type and scale of the development proposed and particular features of the site.
Site Survey - A comprehensive land survey may be required, showing the positions of all existing site features including structures, vegetation, water features, roads and service runs. The survey should incorporate levels with existing contours or spot heights indicated.
Tree Survey - The tree survey should be undertaken by a qualified arboriculturalist, in accordance with the guidelines contained within BS 5837:2005 Trees in relation to construction – Recommendations. The Arboricultural Association maintains directories of approved consultants and contractors.
The tree survey should be drawn up in conjunction with the site survey and should identify on plan the location of all trees in the vicinity of the proposed development site, including those on adjoining land in positions where their roots or branches could impact on the development. In addition to the trunk position of trees, the survey should give an accurate indication of tree crown spreads. The practice of using standard circular symbols rarely reflects the true situation.
To inform the design process, constraints imposed by trees on and adjacent to the site should be plotted on a ‘tree constraints plan’. This should show the above - ground constraints imposed by the size and position of trees (existing and ultimate height and spread of the tree and the potential impacts of shading), and the below ground constraints related to the root system of the tree - a root protection area (RPA). Section 5.2 of BS 5837 provides a means of calculating the RPA. The tree constraints plan will also inform the requirements for tree protection measures on site.
We publish advice on a range of matters including through Frequently Asked Questions on the following topics (clicking on the topic of interest to you will take you to more information):-
Note:
All information contained on this and other pages relating to trees is written for the benefit of tree owners, the general public and amenity groups and answers some of the most common questions relating to trees. It is for guidance only and is not a statement of the law. You should consult a solicitor if you are unsure of your legal rights or obligations.