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Jim Smith: Building for the future - using engineered foundations to protect trees

On shrinkable clay soils buildings and trees can have something of a love hate relationship. Whether the buildings are existing period structures or contemporary development the interactions between building foundations and trees and their root systems is a complex one.

jim smith 002

jim smith 002

Jim Smith is a national urban forestry adviser with Forestry Commission England but the views expressed here are his own

This complexity is increased by the wide variety of tree species that have varying levels of influence on the durability and effectiveness of the foundations supporting the structure above them. However, done well trees and buildings can complement each other and make fantastic places to live and work as well as providing tangible benefits for residents and business users alike.

A property is often the single biggest investment an individual may make in their lifetime and anything that affects that can be hugely worrying if it cannot be resolved quickly and permanently. Often this is achieved by simply removing the tree identified causing the problem and then inhibiting the replanting of trees within the building’s vicinity. This approach is in danger of throwing the baby out with the bath water.

Trees are increasingly evidenced as being critical infrastructure that towns and cities need to rely on in the future if the impacts of climate change are to be mitigated; interception of flash flooding, limiting temperature extremes through shading, and evaporation from leaf surfaces and providing wind breaks, improving air quality and contributing to the health and well-being of city dwellers.

However, these benefits provided by trees are under threat where construction takes place on shrinkable clays soils. This issue is also negatively influencing tree provision in areas without shrinkable clay soils.

Many buildings are continuing to be constructed on traditional strip foundations that, when existing trees are involved, tend to be deep and use large amounts of concrete that is unsustainable in a carbon-conscious world.

On new development sites where no trees exist, use of these traditional foundations at a fixed depth can also inhibit the planting of trees of size and scale. In the planning context tree planting is often dealt with as a reserved item and landscape plans are only approved after the engineering detail has been agreed and costed. This approach limits species choice for tree planting and essentially means trees are a development after thought or precluded altogether as long as that building occupies the site. Building cycles are getting shorter, increasingly large landscape trees are being designed out of our urban spaces as a result of foundation design choices made with no or little consideration of their impact on the subsequent treescape.

How much better would it be, if in areas of shrinkable clay soils, foundations for all buildings were engineered to accommodate trees of scale sustainably? This would minimise use of materials and resources so that the trees could out live successive building cycles and provide mature treed landscapes and increases in tree canopy cover that deliver the most in the way of benefits to the people who live and work nearby. It’s no accident that some of the most desirable places for people to live also have much higher levels of tree canopy cover compared to less desirable areas.

The use of engineered foundations, in particular pile and beam construction methods that permit the harmonious and sustainable co-existence of building foundations and trees must be the preferred choice for the future if the challenge presented by climate change is to be met effectively. Not just to deal with the issue but to maximise opportunities for creating a sea change in innovative construction and environmental improvements that benefit everyone who live in towns and cities in the UK.

  • Jim Smith is a national urban forestry adviser with Forestry Commission England but the views expressed here are his own.

 

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