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What problems occur when building near trees? |
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There are numerous problems associated with building close to trees that may require alterations to your design.
Specially designed foundations and floor structures may have to be used, where there are trees close enough to affect the moisture content of the sub soil. This depends upon the nature of the sub soil, the species of tree and the distance of the tree from the foundations.
All trees draw moisture from the ground with different species having differing water demands (e.g. Oak, Willow and Leylandii have a high demand, whereas Beech, Birch and Magnolia have a low demand). In addition to this clay sub soils are affected by moisture levels i.e. they will shrink with low levels and swell with high levels, and different types of clay are affected to a greater or lesser degree. Sand and gravel sub soils are generally unaffected.
Special precautions have to be taken therefore, where trees are close enough to affect the moisture content of the sub soil. For example an oak tree may affect the sub soil for a radius of 12m or more from its trunk. Due to the way water travels through the ground; the moisture depletion will occur not only where there are tree roots present but will affect a much larger area.
The usual solution to the problem is for the foundations to be taken down to a depth that is unaffected by the influence of the trees upon moisture levels (this can vary from a few 100mm's deeper than normal, to 2 to 3 metres). In addition to this slip membranes and special compressible boards may be required in the foundation design.
In certain circumstances the floor structure will also be affected by the effect of the trees upon the sub soil, particularly where there are very deep foundations or mature trees that have achieved their maximum height. It is usual in these circumstances for a suspended type floor structure to be used (e.g. a suspended timber or beam and block floor).
There are some circumstances where it will be either necessary (due to the complex nature of the problem), or financially beneficial to consult an engineer to design the foundations for the specific circumstances encountered.
N.B. You should also be aware that some trees are subject to Tree Preservation Orders and cannot be removed or pruned without seeking consent from our Planning section. In addition to this if the work you propose requires planning consent, there may be conditions applied to the approval to ensure the protection of the existing trees on the site, regardless of whether they are protected by a Tree Preservation Order. |
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Foundations close to trees
Foundations close to trees
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