Trees and Buildings
Introduction
Tree planting can add considerably to the quality and 'liveability' of new development, creating shade and shelter while providing attractive natural features which complement, soften, assimilate or screen the built form. However, careful consideration needs to be given to the effect of new trees, not only on the development itself, but also on surrounding buildings and spaces. This guidance has been produced to assist those involved in the development process in planting trees in the right locations which in maturity will not create structural or amenity problems to adjacent properties, obstruct important views, or have a detrimental effect on the safety of traffic or pedestrians.For large or complex landscaping or tree planting schemes, a landscape architect should be consulted. They can give advice on every aspect of planting design, implementation and aftercare.
For guidance on existing trees see protection of trees on development sites.
Planning Permission
The Planning Authority may require details of planting proposals to be submitted, either as part of the planning application or at some later date determined by a planning condition. These details will normally include species, sizes of planting stock, numbers, locations, and planting densities. Information may also be required on soil profiles, cultivations and planting methods, plant protection, maintenance and aftercare. As part of the planning application the authority will expect to see good quality site survey information showing details of existing vegetation, soils, contours, the position of underground and overhead services, and any other factors that might influence planting design.Site Selection
Selecting the correct site for planting is critical, in order that new trees do not grow to such a size that they interfere with buildings to the extent that their removal becomes necessary, the following considerations should be taken into account:- The ultimate size of the tree.
- The proximity of buildings, other structures and any underground or over ground services such as telephone and electricity supply cables.
- The potential to obscure any road sightlines or road signs. This can prove hazardous to road users and pedestrians.
- Trees with heavy leaf fall, such as horse chestnuts, should avoid being located near roads, car parks and footpaths where slippery conditions could be dangerous. These trees should also be kept away from gutters and drains.
- Trees such as limes and sycamores which are affected by the sugar secreting aphid should also be avoided in car parks or near seating areas.
Distances between trees and buildings
Trees grow and obstruct daylight. Choose species carefully and do not plant in close proximity to windows.
Trees can cause structural damage to buildings when trees are blown over, most structural damage being caused by the heavier lower limbs and trunks. To avoid concern, trees should be planted no nearer to a dwelling than two thirds of their mature height. However, the limiting factor is more likely to be dictated by the behaviour of tree roots.
Roots
Most tree roots grow in the top 60cm (2 ft) of the ground. The pattern of root development varies greatly between species. As a general rule, roots will spread considerably further than the canopy will extend.
Tree root growth is only capable of exerting a comparably small force, however may cause small structures with no foundations e.g. drives, paths, patios and garden walls to be moved or distorted. Roots are opportunistic and will grow to exploit moisture and nutrients. Fine roots can penetrate minute cracks and joints in drains. Once a small root has entered a drain it can develop a mass of roots, eventually leading to blockage and fracturing of the pipe.
Some species are intrinsically unsuitable for planting close to typical domestic buildings because of the invasive, shallow, or long-reaching characteristics of their root systems. Varieties of Willow, Apple, Cherry, Plum, Poplar and large coniferous varieties such as Leylandii should be used with caution. As a simple rule, they should be planted no nearer than one and a half times their potential height from drains or walls.
Shrinkable Clays
When clay soils are subjected to changes in moisture content, there is likely to be a change in the volume of clay. Tree roots that penetrate such soils can cause the clay to dry out and shrink. Such changes in clay below foundations may cause them to move with resultant damage to the building structure. Conversely the removal of an existing tree may cause the soil to swell when there is an increase in moisture and cause the clay to heave the foundations.
Shrinkable clays are not common in County Durham, but where they are found, expert advice should be sought before planting is carried out. Developers will be required to provide suitably deep foundations and appropriately protected drains to minimise the risk of annual shrinkage and heave. High shrinkage clays will affect the recommended planting distances of trees, and the advice of a qualified arboriculturalist or landscape architect should be taken.
Choice of Species
The choice of tree should depend upon:- Physical conditions at the site, eg, soil type, drainage and exposure.
- The space available for the trees eventual height, crown size and root spread.
- The suitability of the species in the landscape.
Native Species
Where possible, and particularly in rural locations or settlement edges, native tree species should be used. These are likely to have greater value for wildlife as well as helping to assimilate the development into the wider landscape. Advice on native species can be found in our guidelines on trees and shrubs native to County Durham.Conifers
The temptation to choose quick growing evergreens is strong where screening or shelter are major considerations. However, growth may quickly exceed requirements; creating dark conditions and effectively sterilising the ground around the trees or hedging. Relations with neighbours may become strained; particularly if the evergreens are situated to their south or west. Their mature presence may in the future contravene legislation which aims to limit high hedges that block out light or access to a neighbours' property.Mature Height of Trees
The following table may assist you in choosing suitable trees. Poor soil conditions, extreme exposure or waterlogged conditions will affect growth rates, and further advice or information should be sought, as not all listed below will flourish in every situation, and varieties vary considerably.Under 15m:
| Species | Variety | Native? | Average maximum height |
| Apple | Crab | native | 9m |
| Cherry | Japanese |  | various |
| Hawthorn | | native | 10m |
| Judas tree | (Cercis siliquastrum) | | 10m |
| Laburnum | | | 7m |
| Maple | Field | native | 15m |
| Maple | Silver | | 10m |
| Maple | Red | | 8m |
| Maple | Japanese | | various |
| Plum | Cherry | | 8m |
| Sorbus | Mountain Ash (Rowan) | native | 15m |
| Sorbus | hupehensis | | 7m |
| Sorbus | Swedish | | 7m |
| Yew | Common | native | 15m |
| Whitebeam | Common | native | 8m |
| Whitebeam | Varieties | | 12m |
Large Trees
| Species | Variety | Native? | Average maximum height |
| Alder | Common | native | 20m |
| Ash | Common | native | 28m |
| Aspen | (Populus Tremula) | native | 15m |
| Beech | | | 25m |
| Birch | | native | 18m |
| Cedar | Lebanon | | 30m |
| Cherry | Wild | native | 18m |
| Chesnut | Horse | | 28m |
| Cypress | Lawson | | 25m |
| Hornbeam | | | 18m |
| Larch | | | 30m |
| Lime | Common | | 30m |
| Lime | Small Leaved | native | 22m |
| Maple | Norway | | 18m |
| Oak | Various | some native | 23-30m |
| Pine | Scots | | 25m |
| Poplar | Black | native | 25m |
| Poplar | White | | 16m |
| Robinia | | | 18m |
| Sycamore | | | 28m |
| Willow | Crack | native | 18m |
| Willow | Weeping | | 16m |
| Willow | White | native | 18m |
High and Low Water Demanding Species
Not all species or varieties of species listed below are hardy enough for growing locally. The following tables show species water demand in relation to expanse of roots. Those to the left having the 'Highest water demand with furthest reaching roots' and those to the right having the 'Lowest water demands with least extending roots'.Broadleaves
| Highest | | | | | Lowset |
| Ecalyptus | Crataegus | Aesculus | Acer | Ailanthus | Catalpa |
| Populus | Salix | Fraxinus | Castanea | Alnus | Corylus |
| Quercus | Sorbus (simple leaf) | Platanus | Fagus | Betula | Ficus |
| Ulmus | Tilia | Malus | Carpinus | Laquidambar |
| | | Prunus | Gledista | Lirodendron |
| | | Pyrus | Ilex | Magnolia |
| | | Robinia | Juglans | Morus |
| | | Sorbus (compound Leaf) | Laburnum | Sambucus |
Conifers
| Highest | | | | | Lowset |
| Cupressus | Chamaecyparis | Sequoiadendron | Cedrus | Juniperus | Abies |
| | | Thuja | Taxus | Araucaria |
| | | | Tsuga | Ginkgo |
| | | | | Larix |
| | | | | Picea |
| | | | | Pinus |
Further Information
- BS. 5837:2005 - Trees in Relation to Construction can be obtained from British Standards Online
- Protection of Trees on Development Sites
- Planting Trees