Laying firm foundations for resilient homes

In February, the NHBC Foundation published a report examining the increasingly important issue of foundation design, and its role in ensuring that new homes are more resilient to the effects of climate change.

Foundation design is, of course, a crucial aspect of any building – and quite literally the basis of sound design. Getting this right contributes to the integrity, resilience and longevity of a new home.

The report identified two areas of risk that housebuilders, designers and building surveyors should start considering seriously at foundation design stage: the effects of the UK's changing climate, such as increased flooding, and the impact of tree canopy cover on developments.

It predicted that, if global average temperature is on course to increase by 2°C by 2100, annual flooding damages to non-residential properties across the UK are expected to increase by 27% by 2050 and 40% by 2080.

This category still includes commercially owned or build-to-rent homes, as well as offering a good illustration of the scale of risk. For a 4°C increase, the figures rise to 44% and 75% respectively over the same timescales.

In addition, the same report says that risks to building fabric are among 20 requiring further investigation at a national level. These include: 

• desiccation effects in shrinkable clays, leading to subsidence or heave
• higher sea levels in coastal areas, leading to corrosion of foundations from salt water
• damage to foundations and structures caused by wash-out. 

The magnitude of risks to building fabric in the 2050s is categorised as high – defined as costing hundreds of millions of pounds a year – and in the 2080s very high – defined as more than £1bn a year.

These sobering predictions, along with incidents such as the fluvial wash-out damage to a block of flats in Newcastle upon Tyne in 2012, should be enough for developers to consider the long-term viability of the homes they're building. 

Significant rainfall has the power to wash away soils and inundate foundations, compromising the integrity of the structure above.

Buildings with compromised foundations are weakened structurally and are more susceptible to the elements and adverse climate effects. These points were pivotal to the NHBC Foundation identifying foundation design as a key area of interest for research.

Research suggests that even moderate increases in cover in cities can help adapt to the adverse effects projected under a changing climate. Urban trees provide many benefits, including temperature regulation in summer heatwaves by reflecting solar ultraviolet radiation and shading surfaces that would otherwise absorb and later emit radiation.

Properly managed trees also contribute to the planning, design and management of sustainable, resilient landscapes, as they help make developments safer, more attractive and more conducive to health.

There are some factors to be considered by developers when including trees on a site all the same. Poorly spaced trees competing for nutrients and light will not thrive, those positioned too close to properties can interfere with infrastructure and utilities, and suitability of species planted must be considered.

As there are few laws or regulations regarding tree management in the UK, it is essential that developers understand and use trees and canopy cover at the earliest stage of site design and development.

The impacts of increasing canopy cover on building foundations also need to be considered. When incorporating trees in developments – whether newly planted or established – space should be allowed for future growth of roots, stems and canopies to maturity, because these can pose direct and indirect risks to building foundations. The risk of direct contact with structures may obstruct access or light or cause other nuisance, so will need to be mitigated.

As BS 5837: 2012 states, 'where tree retention or planting is proposed in conjunction with nearby construction, the objective should be to achieve a harmonious relationship between trees and structures that can be sustained in the long term'.

NHBC Foundation's report notes that more research is needed to understand the long-term risks posed by climate change and how to address this in sustainable building design.