TREES & FOUNDATIONS

Where your site is overlain with cohesive (clay) soils, you are potentially at risk from sub soil volume change. This means the soil can retain moisture causing it to swell in size and then shrink when dry. This change in volume can be a problem with trees where their roots can drain over time causing accelerated shrinkage. The NHBC dedicate an entire chapter in their construction manual called Building Near Trees; this gives specific tables for foundation depth requirements given the proximity of trees and their heights in known areas of shrinkable soils. Trees are also classified in terms of their water demand; the thirstiest include oak, elm, willow and poplar.