Subsidence: The Hidden Pitfall Of Period Properties

In the contemporary property market, there is a growing demand for historic buildings. Be it a much coveted period property for residential purposes, or a listed building ripe for commercial development, more and more historic structures are being snapped up and converted or restored, for use in the present day. However, it is rarely as simple as merely plucking a structure from the depths of the past and dragging it kicking and screaming into the modern era. These historic gems often present with their own set of problems that require the upmost care and attention. Neglecting to adequately consider the specific and vastly sensitive restoration needs of individual structures will ultimately result in an overwhelming failure, costing monumental sums of time and money, or in extreme circumstances, allowing the possibility of fatalities. 

An abundantly common issue presented by older properties is a lack of structural soundness, often caused by subsidence. When the word 'subsidence' arises, many fear the worst and would happily abandon their building and run screaming for the hills at a moment's notice. However, while subsidence a serious problem requiring immediate attention, it can be managed. The key is recognising the problem, knowing it's extent and formulating an action plan to remedy it.

~What is subsidence and how is it caused?

Subsidence is defined as the downward moment of a structure, as a result of a loss of support from the ground beneath the foundations. Subsidence results in the forming of cracks throughout the building interior and exterior. The severity of the subsidence is directly proportionate to the level of damage inflicted to the property.

A common cause of subsidence is the shrinkage of the soil, under and around the foundations. Cohesive soil, such as clay, is prone to expansion and reduction in periods of wet weather and drought respectively; whereas non cohesive soil, such as gravel, is not as susceptible to these volumetric changes. Non cohesive soil is, however, at risk of diminishing with heavy water flow. If subjected to flooding, for example, the composition of gravel allows for finer grains and granules to be washed away. In addition to individual soil properties, some soil types deteriorate and decompose with time, allowing a susceptibility for subsidence.

There are also a number of human factors that can affect a property's susceptibility to subsidence. Sites that have been previously filled in (such as land fill or mining sites), areas in and around large scale construction sites and locations regularly exposed to high vibrations, will all contribute to the likelihood of subsidence. Previously undertaken, sub standard repair work is also a common factor.

In older structures, trees, shrubs and roots will play a major role in any damage inflicted. Overgrown vegetation may have roots that have infiltrated the soil surrounding the foundations of a building. As a result, moisture is absorbed from these areas and the soil is left vulnerable. Climbing plants such as ivy, also have the ability to grow across a building's exterior, penetrating brickwork and fracturing the masonry. 

~What can be done to fix or treat subsidence?

If subsidence is observed or suspected, a structural engineer is required. A structural engineer will be able to survey the extent of the damage, estimate the likelihood of any deterioration and propose a suitable course of action. In many cases, studying the structural designs of a property and identifying/removing the root cause, will be sufficient to secure a building for many years to come. In extreme cases, underpinning of a property may be required. This is a drastic solution that will only be utilized if deemed a necessity. Underpinning can cause rigidity of structure sections, and thus a great deal of expertise is needed in the undertaking of the same. As previously mentioned, all properties are individual. The extent of action required will be determined by the damage suffered, and, as such, only a qualified structural engineer will be able to accurately advise on the situation. Where possible, employ the use of a structural engineer whose expertise lies in properties of a similar period to that of the property suffering subsidence. This will ensure any repair or restoration work is sympathetic to the materials and character of the property, protecting any period features or charm.