Dealing with Trees
Most houses and bungalows not only share their plots with trees but owe much of their attractiveness to their presence. Yet, trees can be a difficult accompaniment to a home, creating problems both on and off site.
Tree Preservation Orders
- Any application that involves the felling or lopping of trees will attract greater attention from the planners and, if they feel that a tree or group of trees is endangered, they can issue a Tree Preservation Order (TPO).
- A TPO means that it is illegal to do anything that would harm the tree or trees, including lopping or felling them, without the express consent of the local authority.
- This extends to pruning, where only authorised work that will specifically enhance the tree or trees and improve their appearance or health is allowed.
- If there is no TPO on a tree and a proposal to remove it is brought to the attention of the local authority, it can issue an interim order. This will have the same effect as a full TPO and last for six months, during which time the authority can decide whether or not to ratify it and make it permanent.
- Any flouting of a TPO, including harming a tree by chemical means, can result in prosecution and an unlimited fine, together with a requirement to replace the tree. Trees on Crown land, Network Rail land,
- British Waterways land and Highways land are exempt and cannot be the subject of a TPO. Commercial trees for fruit or other purposes are similarly exempt.
- In a Conservation Area any work to fell, lop or prune a tree requires that six weeks’ notice in writing is given to the local authority, during which time it can decide to issue a TPO in the normal way.
- Local authorities have other means of propagating and protecting trees:
- Trees can be protected by inserting a condition within a planning consent.
- A planning consent may also include a condition requiring a tree-planting scheme and a further condition may go on to give the resultant trees additional protection right up to and including placing a TPO on the proposed trees.
- A consent may also include details of just how existing trees will be protected during construction works.
Issues with Foundations
- Although planners and many people like the idea of living in houses close to trees, they can undoubtedly cause structural problems.
- In drought conditions, trees can remove moisture from the subsoil and this, even in otherwise stable conditions, can lead to the ground shrinking beneath the foundations, causing subsidence. This can be serious and, if it persists, underpinning may be necessary. Older houses are probably better able to withstand this onslaught than modern houses as they are more flexible in their construction, and it is possible for a house to have ‘summer cracks’, which heal up in the winter, with little or no injurious effect.
- Roots beneath foundations can rot, leaving voids, leading to settlement. In serious cases, the solution may have to be underpinning.
- Some trees have very invasive roots that can actually crack concrete foundations and it may be necessary to construct a root barrier between the tree and the home. Incidentally Japanese knotweed, an invasive alien species, can have the same effect and is notoriously difficult to eradicate.
- Trees such as willow are frightfully good at detecting water and nutrients and they are quite capable of inserting a small pilot root into a drain and then expanding and blocking that drain.
- In heavy clay situations, trees cause immense problems, especially if they are removed, die or are otherwise weakened. This is because trees take inordinate amounts of moisture from the subsoil and, if they cease to do so, the clay at deeper levels will absorb that moisture and expand.
- This expansion, known as ‘heave’, is unstoppable and strong enough to break foundations. The solution is to construct the foundations in such a way as to negate the pressures, either by taking the concrete foundations deeper and lining the trench with a compressible material, or resorting to a pile and ring beam foundation.
- The NHBC has tables showing the distances that each species of tree ceases to have an effect on foundations, bearing in mind the nature of the subsoil and the rainfall patterns of the region. In many cases this means that mature trees should not be closer than 30 metres without some form of remedial foundation design.
Other People’s Trees
- Chances are that if you have problems with the planners over the trees on your site, it’s the neighbours who instigated them. Remember, however, that once you’ve built your home, you’ll probably be just as protective of the trees that complement it.
- Trees on your neighbours’ land may affect your foundations. That doesn’t mean that you have the right to demand their felling. But it does mean that responsibility for negating their effects is yours.
- If a neighbour’s trees blow down in a hurricane, they may well be liable for the damage caused to your property and their household insurance policy will cover them for their public liability.
- If you identify their trees as dangerous beforehand, they must take the appropriate action, otherwise they might find themselves personally liable for any damage caused.
- If a local authority insists on the retention of a tree that is dangerous, on or in close proximity to your property, then they in turn may be liable for any damage caused.
- If a neighbour’s tree(s) encroach upon your land, then you have the right to lop off any overhanging branches.
Adverse Ground Conditions
Ground conditions are going to vary from site to site and the most common problem types to be found are set out below. But be aware that it is possible to encounter more than one ground condition within a site.
High Water Tables
These can affect construction because as fast as one digs, the trenches fill up with water and become either unstable or impossible to work within. It may mean that a piled and ring beam foundation solution has to be employed. However, in most cases the solution is to use a trench fill foundation where the trenches are filled to within 200mm of the top, as soon as they are dug.
This can present problems with digging foundations. With stable rock it may sometimes be necessary to cut out slots prior to concreting and this may need specialist machinery. Loose shale may present other problems with the trench sides not holding and there may also be an ingress of water. The solution is normally to trench fill.
Possibly the best foundation one can experience, so long as it’s consistent. It has good bearing and good drainage. The problem is that it is often associated with clay and it’s entirely possible for a seam of chalk to underlie clay with the chalk seam diving down almost vertically out of reach of any reasonable foundations. The differential settlement that would be experienced by having part of the property founded on chalk and part on clay may mean especially designed foundations are required.
These may present problems with the trench sides collapsing. Certain types of sand are known as ‘running sand’, where the sand is waterlogged and has the consistency of treacle. This is impossible to dig and the solution may be a pile and ring beam foundation, or a reinforced concrete raft.
The peat may be extremely deep and due to its propensity to shrink on a seasonal basis when it dries out, provides unsuitable bearing. The solution is either a pile and ring beam or a raft foundation.
In many areas, where it is relatively friable, mixed with sand or gravel, it is not a problem. In other areas where the clay has a high plasticity, it can present difficulties, particularly if combined with the presence of trees. Trees take vast amounts of moisture from the subsoil and clay has a propensity to increase in volume when it is wet. If a tree is removed or damaged then it will cease to take moisture from the subsoil and the dry clay will take on that moisture and expand. This causes ‘heave’, where the ground will then rise to the detriment of any foundations. The solution is first and foremost deep trench fill foundations. But there is a limit to how deep they can go and, at some stage, the solution may be to swap to a pile and ring beam foundation.
Made Up or Filled Ground
An indicator may be broken bricks, tiles or pottery in the spoil. Where a site has been ‘made up’ with imported material, it is known as a filled site. This is difficult to build upon because there is no consistency of bearing. The solution is normally a pile and ring beam foundation.
If coal or any other organic and combustible material is found in the foundations, it will normally have to be dug out.
In some cases, although the ground within foundation depth has good bearing, faults beneath that level or deep in the ground, such as mining, may mean that the ground is liable to subsidence or movement. The solution is often a reinforced raft foundation.
In many areas – particularly where the under lying rock is granite – a naturally occurring radioactive gas can seep up to the surface. If this collects in houses it could possibly increase the risk of cancer. The foundation slabs of any building with a solid oversite must be made gas-tight using a membrane linked into and sealed to a cavity DPC (damp-proof course). With a suspend – ed concrete floor or beam and block floor, there must be a membrane beneath the screed linked into the DPC and there must be cranked ventilators, allowing build-ups of gas beneath the floor to escape harmlessly.
Making an Application on a Tree-heavy Plot
Most local authorities are concerned not only to protect trees that already exist, but to enhance the local area by a requirement for tree planting to accompany any new development. They are assisted in their endeavours by a huge body of public opinion that acts to inform them of any ill that is being carried out or proposed to trees and they are backed up by quite draconian powers of intervention. If you plan to make an application on land that has trees on it, careful consideration must be given as to the procedure:
- If there are TPOs on any trees prior to the application being made then, unless the local authority is in agreement with any necessary felling or replacement, you could fail.
- If there are no TPOs on the land and an application is made for planning permission, which would result in the necessity to fell trees, the local authority, probably at the prompting of locals, may well impose a TPO that would result in the application’s failure.
- If planning permission is granted on land and the local authority was to subsequently impose a TPO that had the effect of making the consent inoperable, then the local authority may well be liable for compensation.
- Negotiation to replace a tree or trees, preferably with a more advantageous and native tree, may well be successful. However, there is no certainty of this.