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Foundations near trees What is deemed appropriate when building near trees is producing more comments. Brian Pyle refers us to damage occurring even in areas implied to be deep enough to be stable in the NHBC recommendations. He also provides other warnings: The paper on NHBC Standards published on 16 August may encourage a greater use of the guidelines in the design of foundations. The experience of our practice dictates a need for caution in respect of the following: Zone of influence. A typical experience of damage from tree roots is from a 20m-high oak tree, 20m from the corner of a Victorian property with a cellar. Significant clay shrinkage on a medium plasticity soil had been experienced at the depth of the foundations to the cellar 2.5m below ground level at the distance of 20m. This is way outside the guide graphs. Differential subsidence had created a crack width of nearly 20mm, at roof level, which almost closed during periods of very wet weather. We advocate the use of the term ‘differential subsidence’. It explains precisely what has occurred (Verulam 16 August). Verulam