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Consulting Engineers

Ways to get around protected trees

What can be done if you want to develop near trees with a tree protection order (TPO) on them. If you want to develop a building on a site that has a TPO on it, there are various ways that you can do this without harming the tree. The easiest and cheapest way is to avoid the area around the tree that is approximately the size of the crown of the tree. However, sometime this is not possible as it will remove an important area of the development.

Sometimes, depending on the required size and position of the foundations, these can be carefully hand-dug, as long as they avoid the major roots of the tree, which are generally with a diameter of 25mm or more, but this may depend on the type of the tree and the root spread.

A more economical and practical solution often is the use of mini-piles, which can be inserted within the tree protection area without damaging the major root systems. The new building can then be constructed with a suspended ground floor slab supported on a grillage of beams spanning between the piles. This will reduce the potential load on the soil in the tree protection area which will benefit the tree, and mean that the development can proceed as long as carful installation methods are adopted and followed.

This means that a development can be successful despite having trees with TPO’s on them on the site. The use of the mini-piles as a foundation solution will also mean that the trees will not affect the soil due to their water demand as the loads from the building will be transferred to much deeper levels in the soil that will be affected by the trees.

This shows that buildings and trees can exist in harmony on a site as long as the building is designed to take the trees into account from the beginning, not as an afterthought.

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