Building near trees.

I was asked if you need to make foundation excavations deeper when building extensions near trees?.

It depends on the ground conditions. If the ground consists of heavy clay then the Building Control Officer will generally ask you to take the excavation depth down to the NHBC guidance for Building Near Trees.

The guidance gives suggested depths of foundations in relation to the soil type and distance of trees from the foundation.

The NHBC guidance on building near trees has great information regarding tress, foundation depths, types of suitable foundation etc. This can be purchased by designer /clients etc.

For domestic construction the Building near trees can be applicable to extensions, conversions and new dwellings.

If you wish to deviate from the NHBC guidance you can have independent soil tests carried out by an approved person. This option may allow you to excavate to a lesser depth than the NHBC guidance suggests, however most people tend to follow the NHBC guidance.

Trees such as willows may cause foundation depths to be deep depending on the distance from the foundation.

Conifers are one of the most common trees that are in proximity to proposed extensions etc due to their popularity and rapid growing rate.

From a design point of view it is well worth excavating one or two trial holes at design stage to establish the foundation depth, which in turn wil allow for a more accurate specification for pricing purposes. This isn’t common practice, however it is very advisable.

Additional information on foundations can be found in Approved Document L1 A

Another worth while exercise for designing house extensions is to carry out a Public Sewer check before submitting to Building Control.

This is advisable purely because if there is a Public Sewer within three meters of the proposed extension you will need permission to build from the Water Authority and in some cases they may not grant permission. More often than not you do get permission.

A public Sewer check is also part of the Building Control plan vetting service. But to have piece of  mind it may be worth doing this in advance.

You can usually have a Public Sewer check carried out by the Local Authority for free.

Please contact us if have any questions regarding building near trees..