Grand Designs but Grim Drainage

Property construction plans

Over the last few years, super-basement conversions have become more and more popular. There are double reactions about this kind of renovation with homeowners loving the extra space they provide, while neighbours often find them concerning, disruptive and sometimes dangerous.  

These basement conversions are especially popular in London, where space is at a premium, and although this trend is growing at a slow rate, there have been concerns from different stakeholders and individuals who feel this could spell doom for the city.

Why are basement conversions becoming popular?

House plan with basement

Most experts agree that the most influential factor encouraging homeowners to embrace underground excavations is the urge to get more space at a lower cost. It’s estimated that the housing demand of London stands at 4 million homes needed within the next 20 years. With limited space and resources, it becomes challenging to have this mark attained within the set time.

Adding a basement to, say a two storey building, will add around 50 percent more floor space, and this is without necessarily increasing the footprint of your home or using valuable garden space to facilitate an extension.

But that’s not to say that basement extensions are not without their drawbacks, and if not carried out correctly, they can result in a whole host of problems! From ground subsidence and neighbour disputes to costly and unpleasant drainage issues and sewer pipe problems. There are a whole host of easily overlooked issues that should be considered and guarded against before any work begins.

Planning permission

Every council has laws that control building projects and major renovations to existing structures. However, some basement conversions may not require approval, especially if such renovations are considered minor as described by the authorities.

It is likely that only new basements, which require major works and a restructure of the external appearance, will need approval.

With this in mind, it becomes possible that many of these extensions may be implemented with little or no regard to safety and the environment, something that has seen many neighbours engage in legal tussles due to the repercussions of poorly constructed basement extensions.

Most drainage systems in London are designed to serve neighbourhoods that have the usual structures and demands. So if an underground basement is constructed without considering this fact, it can result in damage to the pipework and overwhelmed systems. This could also make it difficult to address any existing problems within the drainage system.

Party walls violation

Basement drainage pipes

According to the Party Wall Act of 1996, if your house is semi-detached or terraced, and you may end up excavating into your neighbour’s walls, there are certain regulations that must be followed.

Most problems that arise during a basement conversion project are disputes with neighbours. Excavating for the extension may compromise the stability of the neighbours’ structure, and many fear that having a basement construction near their homes could cause subsidence within the foundations of their homes.

You must consider the impact that any work will have your neighbour’s property, and notify them, giving them the opportunity to consent to or oppose the works.

Party wall regulations also apply to shared drainage systems, so it is essential the drains are mapped and investigated before work begins to identify the potential impact of any work.   

If these regulations are violated, and the project is implemented without thorough investigation and an agreement with the affected neighbour/neighbours, it could result in a risk to the integrity of the structure and leave both your property and your neighbours’ properties vulnerable to natural catastrophes like floods.

Possible failures

Flooded basement requiring water extraction

British Structural Waterproofing Association views building basements as a hazard, and they do not recommend the construction of such buildings especially where the water table is high. If the water table is higher than the underside of the basement slab, this poses a significant risk as problems arise when the natural water level exerts pressure on the walls of the basement.

If the waterproofing is not well constructed, there are high chances of water penetration and leaks within the build. This will not only compromise the stability of the structure, but could also present a health hazard if the water is contaminated with wastewater.

Health hazards

The drainage and sewerage system of London is immense, having been redeveloped in the late 19th century. Although it has been extended as required over the last century, it is now undersized for the current high population and most of the system is over 100 years old.

This means the drainage systems are running at capacity in general day-to-day usage without adding rainwater, and with the amount of properties in London, the system is under constant strain. Without extensions for each new development, it can easily become overwhelmed.

This is common in areas such as Fulham and Chelsea, where generally the sewers are combined foul and rainwater systems, so when heavy rains or floods occurs, the sewer system receives more wastewater than it can accommodate.

This can lead to backfill, whereby all the lateral junctions of the system are filled to capacity and result in wastewater flowing back into private household drains. If the property affected has a basement then gravity can cause the back-flowing sewage to leak from the drains, internal toilets, sinks, etc, and flood the basement with sewage and wastewater. The damage from drainage floods can be a hazard to health, very unpleasant and very costly to put right.



Express Drainage Solutions

Here at Express Drainage Solutions we specialise in drain mapping and CCTV drainage surveys that will chart the structure of your entire drainage system, and identify any potential areas of concern.

Once identified, our expert team can provide proactive repairs and maintenance work that will ensure your super basement extension avoids the potential pitfalls of an inadequate or degraded drainage system. We can also perform party wall surveys of your drainage system that will satisfy your legal duty to consider the impact of your extension on neighbouring properties.

Want more information?Contact us today on 020 3124 1785

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Category: Drainage


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