Tackling the challenges of basement flooding

January 5, 2023

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By Dean Harding-Dempster, technical practice group lead, building consultancy division

The number of basement constructions and conversions have dramatically increased in recent years.

Adding a basement is a more cost-effective way to provide additional space than moving or upsizing and adds significantly to the overall property value. Planning and conservation hurdles aside, it’s easy to understand why this has become an attractive proposition for High Net Worth (HNW) clients.

Basements have become so popular in the UK that at least one London local authority has had to introduce restrictions to control the number of applications processed. In London, there were over 7,000 applications approved between 2008 and 2019. Homeowners can then convert an existing, refurbish or create a new space based on criteria set by British standards and building regulations depending on the nature of the work. While basements unquestionably add to the market value of a home, they can prove to be complex structures when dealing with perils . With the onset of climate change, damage caused by flooding is another common concern for properties with basements.

Real-world examples

In Littlehampton, a seafront Victorian terrace experienced flash floods following heavy rain. The water receded quickly and contractors entered the site to address the damage. Exposure appeared to be limited. The initial external surveyor advised to strip the basement floor, door linings, wall render, etc. but was unsuccessful in mitigating the damage long term. The property succumbed to persistent dampness and the basement walls were not drying properly which extended the timeline. When Sedgwick’s experts were called in, we found that behind the property there was an opening to the crawlspace which hadn’t been observed. Once we found the cause of the ongoing damage, we were able to move forward with the repair process.

In another instance, our experts came across an ingress of water in a basement that was likely due to negligence by the building contractor or previous drying company. Without a thorough inspection, wall plaster had been removed despite uncertainties about the type of basement construction. As a result, the waterproofing mechanism was compromised which led to large pay-outs for strip-out work and drying. Using correct drying techniques is critical as not every basement structure is the same.

Basement perils

Flooding affects basement construction differently depending on the type of waterproofing mechanism used and the level of saturation. Three issues that adjusters often see is moisture migration through the structure, a burst pipe or escape of water and flooding due to heavy and persistent rain levels. The drying process can often go on longer than anticipated. Where structures become difficult to dry, it may be an indication of a failed or absent waterproofing mechanism, so it’s important to gain an initial understanding of the three types of basement construction and how to best deal with a basement affected by water. Over time, the hope is that basement designs will be more effective in mitigating flood water damage. Meanwhile, our experts in building consultancy are on hand to advise where necessary. Adjusters should bear in mind the risk associated with tackling a basement that hasn’t been constructed in accordance with relevant standards or has begun to fail before the peril.

Basement structures and water proofing systems

There are three types of basement structure and water proofing systems used in building work. Type A is known as a barrier protection which is commonly found in basements, semi-basements, retaining walls, car parks and storage rooms etc. With the form constructed from concrete or masonry, there is only limited protection against the ingress of water. Protection is therefore primarily dependent on application of the barrier system. A type A system can often be the most challenging system because when someone who doesn’t understand basements gets involved, it can be subject to damage when the wall render is disturbed.

Type B is known as a structurally integrated protection – designed and constructed in reinforced or pre-stressed concrete to minimise and/or prevent water penetration dependent on the chosen grade of basement use.

Type C is referred to as drained cavity protection which is made from structural concrete or masonry to minimise the ingress of water. Any water that does find its way into the basement is channeled, collected and discharged in a cavity created through the addition of an inner skin to both walls and floor. The water is either collected in a sump and mechanically discharged or is drained by gravity where possible. Failure of pumps and drainage channels remain a regular cause of failure to Type C systems. To establish the type of basement structure, it’s recommended to request documentation from the customer, and to instruct a qualified Sedgwick surveyor to complete the assessment.

The building regulations for basement constructions deal with moisture resistance, electrical safety, means of ventilation, sound resistance and means of warning and escape. However, flooding continues to put these properties at risk. Whether a basement is under construction or being refurbished, the risk of water damage is a consideration today and for years to come, and it’s important that whilst managing clients’ expectations, we also manage the risks to ourselves. Our building consultancy solutions enable our clients to manage costs efficiently and make accurate, informed decisions which contribute to their business success. If you have any questions about the complex area of basement flooding, contact [email protected].

Tags: assessment, basement, basement construction, building, building consultancy, Building consulting, building regulations, construction, flooding, high net worth, HNW, Property, Property claims, Property damage, property owner, Restoring property, UK, United Kingdom, water, water damage