Calls have been made for the ground engineering industry to be more proactive in supporting the domestic basement market and provide specific guidance for client, planners and designers.
GCG senior geotechnical engineer Apollonia Gasparre and associate director Philip Smith said that industry guidance was needed during a presentation at Ciria’s Geotechnical issues in construction conference yesterday.
Gasparre said that C580 guidance for embedded retaining walls is sometimes applied to domestic projects but asked if this was appropriate. “Road tunnels and commercial basements are usually large scale developments but the size of domestic basements can be highly variable,” she said.
Smith added: “C580 is often used for domestic developments as there is little alternative for projects where there are concerns over ground movements.”
According to Smith, there are still too many domestic basement projects that do not have any engineering input. “They are often approached in the same way as an extension,” he said. “Any assessments for the planning application are completed ahead of detailed design. Often there is a lack of ground investigation with no knowledge of groundwater, which can have a significant effect on the choice of construction method and potential for ground movement.”
Smith and Gasparre acknowledge that Basement Impact Assessments are required by London boroughs but they questioned how authorities outside of the capital approach planning applications.
“Kensington and Chelsea has developed a policy of restricting all basements to one level to try to minimise issues but I feel that as an industry we have shot ourselves in the foot by not being more proactive in offering guidance specific to the domestic basement sector,” said Smith.
“Clients need assistance in understanding the process, the issues and who to employ. Planners need a more unified approach and designers need to understand the need for appropriate ground investigation and access to empirical ground movement data.”
Delegates at the conference largely supported the development of guidance and Byrne Looby David Beadman director David Beadman called for the guidance to cover the effects of basement construction on neighbouring properties more comprehensively. “Basement construction below a semi-detached or terraced property is often facilitated by underpinning of the party wall, which is good for the basement but it leaves the remaining walls of adjacent property floating,” he said. “I think that as an industry, we should be telling clients that the underpinning should extend further under the neighbouring property so that support feathers out. There is a strong need for guidance for engineers working on domestic basements.”
Another delegate added that many schemes do not have any engineering involvement, even where the construction conditions would be considered challenging.