Most trees that grow near buildings do not pose any danger to the buildings. However, specific trees have rooting systems that go very far, up to 4-7 times the diameter of the foliage. As such, they can be a threat to the structural integrity of surrounding buildings.
In order to accurately assess whether your home or property is endangered by the surrounding trees, it is important to understand the factors that determine whether or not a tree is a danger to a building. Read on for common questions related to this.
1. What determines whether or not a tree endangers a building?
Tree rooting systems spread according to the species of the tree as well soil conditions and size of the tree. For instance, trees in non-clay soils will often not extend too far from the stem and hence pose little risk. Roots are opportunistic and will spread further where they encounter no resistance. Single trees are likely to have wider roots than trees planted in clusters. Also, places with high bedrock or high water tables will limit downward growth of tree roots, making them more likely to spread outward and endanger surrounding buildings.
2. What is water uptake and how does it affect danger to buildings?
Rooting systems spread to carry water to the tree stem, and larger trees will take up more water. Also, different water species have different water demands. The following is a list of a few common trees and their water demand levels.
Low water demand – Catalpa, Liriodendron, Morus, Magnolia, Liquidambar, Corylus, Sambacus (elder), Pinus, Picea, Larix, Ginkgo, Araucaria and Abies
High water demand – Salix (willow), Populus (poplar), Eucalyptus, Quercus (oak), Chamaecyparis (cypress), x Cuprocyparis, Cupressus (cypress)
If your tree species isn't named here, you can always check online to find its demand levels. Most other species have intermediate water demand. If you're worried about a tree in your lot, a certified arborist can help to allay your fears.
3. Does pruning reduce the danger of subsidence in my property?
If you've found that one of your trees contributes to subsidence but still want to keep the tree, you may want to think about the effects of simply pruning rather than felling the tree. Tree reduction can reduce the level of water uptake and degree of movement of roots, and so it could be a viable option.
However, to make a lasting difference, you'll have to prune most of the crown volume. A little pruning will simply encourage more shoots to sprout and the leaves to become larger and hence isn't very effective. In addition, pruning will have to be repeated every two or three years when moisture uptake by the tree returns to normal.
Contact a tree services company if you're concerned about how your trees are growing.