Trees and Vegetation

trees and vegetation cause subsidenceWhere risk factors appear to be significant and trees are close to the property, reasonable vegetation management may be appropriate. However, the pruning of trees to reduce water absorption is not considered to be a particularly effective remedy and it may be necessary to consider removal of trees where other risk factors are high.

Tree management strategies are considered to mitigate any future risk due to growth and that advice is sought in relation to future plantation schemes – it is advisable to consult an arboriculturist (trained and qualified in the cultivation of trees and shrubs).

Some key considerations:

  • If the trees are too close and were planted after the property was built they might be relocated if of a suitable size. Read more.

    During a drought period these trees will have more of an influence as the tree roots extend to find moisture deeper and further away from the tree. If it is impractical to move the vegetation, ensure it is regularly managed to control the moisture uptake. This can be achieved by crown reduction and crown thinning.

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  • If the trees are too close and were planted before the property was built – manage them by crown reduction and crown thinning. They should not be removed without specialist advice as this could cause uplift of the ground (i.e. heave) which can result in structural damage.

The removal of trees, however, requires general consideration as trees in the urban environment make a very significant contribution to people’s quality of life and research has found that the majority of people who live close to trees value the benefits that they bring.
Read more.

Apart from their aesthetic qualities, trees provide a number of practical benefits in the built environment. They improve air quality, reduce wind speed, save energy and reduce the urban heat island effect caused by the build-up of temperatures in hot summers. It is the intention that tree cover in urban areas should be increased and in many cases this has been written into government or local policy. In London the intention is to increase tree cover from about 20% to 30% of land cover.

There are two standard arboricultural pruning techniques used to reduce the crown size of mature trees. The first, crown reduction, reduces crown size but allows the ‘natural’ shape of the tree to be preserved. This involves an overall reduction of both height and spread by removing the outer portions of all major branches. The second technique, crown thinning, reduces the number of side lateral branches coming off all the major branches not affecting the original volume of the crown but reducing its density. For both techniques the normal industry standard is to aim to reduce the canopy leaf area by up to 30% depending upon the species.

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Tree Preservation Orders and Conservation Areas

Before undertaking any tree works it is important to investigate any legal constraints. If the trees are protected by a Tree Preservation Order, or your property is located within a Conservation Area, they can only be pruned or felled with permission from the Local Planning Authority.

 

What if the trees are not on my property?

Neighbours

If the tree is in a neighbour’s garden (owned or rented), a sensible and non-confrontational approach is advised, and endeavour to get them to seek and take appropriate action. Only if your neighbour is uncooperative should you then write to them (we have a prepared letter if you wish) and keep a copy of the letter. Subsidence Support Services

Council or Commercial Property

In the event that the tree is owned by the Local Council or a business then the first stage will be to write to the relevant department or the Company Secretary of the business. The letters should remind the legal owners of the duty of care to ensure that the vegetation is maintained - we do have a prepared letter for use if required, and can provide individual support if you so wish. Subsidence Support Services

 

Drainage

Take care to ensure that gutters, downpipes and drains are in good repair. Excess water leakage or discharge can cause soil softening beneath foundations. Older drainage systems can sometimes leak and poorly sealed joints can also allow tree roots to enter the drain causing blockage and further leakage.

It is particularly important to carry out these inspections on older properties where the drains comprise of salt glazed clayware pipework. With this type of construction, roots entering at the pipe joints is not uncommon, this can cause blockage and hence leakage in the system (i.e. water backs up and leaks through the pipe joints)

As a minimum it is recommended that manholes are lifted and inspected on an annual basis. If there are concerns over the integrity of the drainage system a specialist CCTV survey can be undertaken to assess its condition. Subsidence Risk Survey – Drainage Report

 

crack in a wall caused by subsidenceI’ve found a crack in my house what should I do?

Cracks in houses can be caused by a number of reasons. The following provides a guide of the types of cracking you would usually see with subsidence:

  • Vertical and diagonal cracking concentrated in specific areas and tapering in width between the top and bottom of the property
  • Cracks extending through the damp proof course (dpc) down into the foundations
  • External cracking reflected internally in the same area of wall
  • Rucking of wallpaper at corners between walls and ceilings
  • Misaligned/distortions of openings in the structure (windows and door frames which are weak points in the structure of the property), causing doors and windows to stick
  • Cracks appearing after a prolonged period of dry weather
  • Seasonal opening and closing of cracks

crack in house caused by subsidenceIf the cracks are as described above or you suspect it is subsidence then the sooner it is diagnosed the better. Firstly check that your buildings insurance covers subsidence. Most insurers will be helpful in dealing with a claim – they will recommend specialist advice.

A Chartered Structural Engineer or Building Surveyor - Subsidence Risk Survey – Specific Defect - will be able to work out whether or not there is subsidence and what the likely cause is.

The insurance company will advise you on the next steps to be taken. Where appropriate, specialists will be appointed to investigate the cause of the damage and to arrange for repair work to be carried out (the effects of even quite serious subsidence damage can often be rectified by means other than under-pinning).

In the most serious cases, the investigation including monitoring of the movement causing the damage can take a considerable period of time in order that a proper and lasting repair is made to the property. Where monitoring of this nature is required the time taken by the investigation work may well exceed 12 months.

Please note that most household insurance policies require policyholders to pay the first £1000 (the normal “excess” figure) of a subsidence claim. You should prepare to meet this expense.