2009 - PCA Basement Conversions Feature

Basement Conversions – A Trend On The Rise

 

The current trend towards improving rather than moving - coupled with a general shortage of suitable building land - means developers, commercial owners and householders are increasingly looking to make the best use of the space they can.

 

As a result, the UK is seeing basements – both new build and retrofitted - become increasingly popular.

 

In tandem, the UK’s structural waterproofing industry is being called upon to deliver a safe, secure watertight solution for underground living. Here Yasmin Chopin, executive director of the Property Care Association (PCA) gives an insight into the popularity of basement structures and a general guide into methods of waterproofing.

 

 

A Growing Market

 

“For some time now, the trend has been to look upwards when increasing the size of properties, with developers building taller new-build three-storey properties and existing homeowners looking to loft conversions.

 

However, more people are increasingly starting to think below ground as an effective means of freeing up more space too.

 

Across the UK, the trend for basement development is on the rise. Even in this time of recession, the PCA - the trade body representing professionals in the structural waterproofing industry - has seen a large-scale rise in the number of contracts undertaken by its members to waterproof basements

 

The benefits really add up. A basement can enlarge the floor space of a two-storey property by up to 50 per cent without increasing the footprint of the building – and such projects offer a cost-effective solution too.

 

Modern basements, created in new-build developments or retro-fitted to existing properties, provide light, airy living spaces, which can even incorporate windows or light tubes to allow use of natural light.

 

Trusted technology and techniques also means older basements and cellars can be modified and refurbished into modern-day living spaces too.”

 

 

Getting The Right Level of Expertise

 

“Structural waterproofing below ground is a highly specialised operation and must be undertaken by contractors and designers who have the requisite levels of skill, understanding and experience. Failures resulting from inadequate specifications or poor workmanship can be very costly.

 

Even in areas with high water tables, an effective solution can be introduced to keep structures watertight. However, if this crucial factor is overlooked, the results can be devastating.

 

In extreme cases a poorly waterproofed basement can be subject to catastrophic flooding, which could destroy all the contents of the room, but more commonly simple dampness of the atmosphere can make the space cold, uninviting and cause deterioration of items sensitive to damp.

 

PCA members who specialise in structural waterproofing are able to work with the client, architects, structural engineers and homeowners to design a suitable waterproofing solution.

 

Members of the PCA must demonstrate an understanding of the BS8102 (Code of Practice Protection of Structures Against Water From The Ground) standard and the Association’s own Code of Practice for underground waterproofing.

 

The PCA also requires that surveyors providing guidance on waterproofing must demonstrate their competence by gaining the Certificated Surveyor in Structural Waterproofing (CSSW) qualification.

 

PCA members can also offer long term guarantees, through GPI, which is regulated by the FSA.”

 

 

The Types of Waterproofing

 

“BS8102 (Code of Practice Protection of Structures Against Water from The Ground) provides the basis for basement waterproofing design. The code describes three forms of construction that can be employed when creating dry rooms below ground, Type A, Type B and Type C.

 

Type A is usually referred to as ‘tanked protection.’ These are structures that have little or no integral protection against water penetration and rely totally on a waterproofing membrane to keep water out. This type of waterproofing can be applied to masonry or in concrete structures.

 

If a waterproofing membrane is included during the construction of the cellar, it may be applied internally or to the outside of the structure or, in some cases, sandwiched between two skins of masonry or concrete. Multi-coat renders, cementitious coatings, epoxy resin systems and adhered bituminous sheeting are examples of Type A waterproofing.

 

Type A waterproofing is ideally suited to many types of waterproofing projects in both new build and renovation. Product selection, design and application are critical.

 

Structures built with a water resistant shell are referred to as Type B waterproofing systems. These will usually be constructed out of reinforced concrete to an appropriate design code, such as BS8110 or BS8007, which gives guidance in the grade of concrete to be used and spacing of the reinforcing steel.

 

This type of waterproofing system is predominantly used in new build basements but can also be considered in some retrofit cellar applications.

 

Type C or ‘drained protection’ systems are now very common in basement renovations and conversions, but their use is growing in new buildings as well. Type C systems rely on a drained cavity within the basement structure. There is a permanent reliance on the cavity to collect groundwater that enters through the fabric of the structure. The drainage system directs the water to a drain or sump, where it can be removed from the building by gravity or pumping.

 

Type C systems have developed rapidly over the last two decades. PCA contractors now have access to some fantastic products.

 

These include, high-density drainage membranes, advanced sealing and fixing systems, purpose designed perimeter drainage channels and state-of-the-art sump and pump packages. Most pumping systems now incorporate back-up pumps and batteries and an audible alarm. It is even possible to install a system that will call people on their mobile phone if it detects a fault.  

 

Overall, the choice of waterproofing methods appropriate to the individual conditions of the build is vitally important and such a judgement is best undertaken by a PCA specialist waterproofing surveyor.”

 

 

Further information

To find a PCA member across the UK property professionals and developers, as well as homeowners, log on to the Property Care Association’s web site on www.property-care.org and select the ‘Find a Member’ option.

 

The PCA also offers a free online resource centre to highlight the space that a basement conversion can free-up.

 

What Lies Beneath? brings together a wealth of information within one easy-to-navigate web page, to show what a basement conversion involves.

 

www.property-care.org/basementconversions includes in-depth technical background data, case studies, a short video and images.

 

 

Q and A – Basement Conversions

 

Despite the recession, the Property Care Association reports that conversions have increased by at least 100 per cent over the last three years.

 

So what does a typical basement conversion cost – and why should such a project be carried out?

 

Here, Steve Hodgson, deputy director of the PCA, gives an insight into some commonly asked questions.

 

How much does a basement conversion cost?

 

It is very difficult to give an accurate price, but for £25,000 a typical terrace in London can have a new basement converted from an existing structure. This would include electrics, walls, floors and plumbing extension works.

 

To dig out a new basement is much more difficult to price as there are many variables. Looking at the London area again as an example, some areas of the city are on clay, some are on silt, and that alone will affect the construction process.

 

Is a basement conversion cost-effective?

 

Whatever the project, it has been shown time and time again that the creation of a new basement is a rewarding and cost effective investment.

 

How popular are basement conversions in the UK?

 

The number of basement conversions, both the creation of new basements and the conversion of existing cellar into dry useable rooms, has increased dramatically - I'd estimate by 100 percent in the last three years alone – even in the current downturn, basement conversion figures are rising. That figure might be even higher.

 

This growth is because of the tried and tested technologies now available to create basement conversions, the demands on land space in the UK and the fact that the space created is flexible and very usable.

 

 

New PCA Guidance for the Service of Drained Cavity Waterproofing Systems.

 

Many occupied basements are protected from groundwater using a drained cavity. This tried and tested form of waterproofing is described in BS8102 as Type C protection.

 

 Any water entering the specially designed cavities is allowed to flow through the system freely so that it can be channeled to a sump or other point where it safely be drained or pumped away.

 

In order to ensure the long term integrity of this type of waterproofing, the pumps channels and other drainage elements must be kept in good condition and free of obstruction. This is achieved by regular planned servicing and maintenance.

 

BS8102 highlights the need for service and maintenance of Type C waterproofing systems.

 

 

Now, the PCA has published new guidance that looks at the service and maintenance requirements of drained cavity waterproofing systems, to reinforce the importance of such intervention for contractors and clients alike.

 

This valuable document will provide assistance to those responsible for the design, installation and service of Type C systems and should guide anyone who owns or occupies a property that is protected by this type of waterproofing system.

 

‘Guidance for the Servicing and Maintenance of Drained Cavity Waterproofing systems (Type C)’ is available now and can be downloaded free from the PCA website by registering at http://www.property-care.org/property-professionals

 

For more detailed guidance on service and maintenance of drained cavity waterproofing systems contact the Property Care Association on 0870 121 6737 or see http://www.property-care.org/files/service_and_maintenance.pdf