29 Oct 2019

Leave waterproofing to the experts

Stuart McGinlay, Structural Waterproofing Designer at Wise Basement Systems, explains why approaching a self-build requires waterproofing consideration.

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One couple in the West of Scotland had a dream: to build their own home and live in it. Mr & Mrs Smith found their spot by Corsewall Lighthouse Hotel, tucked away in a scenic coastal area with a view of the famous Lighthouse and the Irish Sea in Stranraer, Dumfries and Galloway.

They designed the house together, and wanted to be project managers, so they could closely oversee the build and ensure their personal touch ran throughout the stages of construction.

Self-building a home can often be cost-effective, saving money over time – especially if you employ the contractors yourself. The Home Builders Federation estimates the average self-build home to be £146,000 if you employ builders (£84,000 if you can do the work without contractors).

House prices on the coast of Scotland can reach £342,346 according to a report by the Bank of Scotland last year, so if you have the time, the will and the way, then a self-build is an attractive option.

Waterproofing is a must for any type of construction project, but if the plot of land is by the sea then unique jobs often become paramount to ensure the premises don’t have any issues with water ingress in their basement. For example, Mr & Mrs Smith’s self-build was in a hilly area where rain water would run down the bank, and of course an oceanic climate exposes a home to all of the elements.

The Stranraer job

The Chartered Institute of Building states that 75% of building failure is the result of water ingress – with failures leading to structural problems, mould, corrosion and other moisture-related issues such as dry rot. Managing this element of construction isn’t something the Smiths wanted to risk, so they called in the experts to look at what could be done to their property.

Wise Basement Systems offered full consultancy at each of the waterproofing stages for the client to sign off and fully guaranteed upon completion. External waterproofing and a drainage system was first required for the standalone house, before an installation of what is called an ‘internal Type C Newton 500 system’. Once the builders have built the house itself then Wise Basement Systems will return again to finish waterproofing the outer building.

What do I need to know?

The National House-Building Council (NHBC) consistently reviews its guidance and requirements around structural waterproofing. Its published standards make it clear that any waterproofing project must include early input from a waterproofing design specialist. There are three grades of protection when it comes to waterproofing, which are based on the intended use of the property. Homes typically fall into Grade 3 protection, which means they must maintain a completely dry environment with adequate ventilation.

This level of protection will ensure damp cannot penetrate the living area of the building. It must always be remembered, that once a basement is water tight, any moisture created by occupancy needs removal by suitable ventilation, otherwise condensation can become an issue.

We always recommend getting a Property Care Association (PCA) qualified Certificated Surveyor in Structural Waterproofing (CSSW) involved in any new-build or conversion project. Not only is it the best way to minimise risk, but they will help you to understand the costs of waterproofing – which can represent a significant proportion of the total costs. This is particularly true if the property requires structural support to accept a new basement or update an existing basement.Types of waterproofing In any below ground space that falls into Grade 3 and/or high-risk environments, two different types of waterproofing systems are recommended, in-line with the NHBC’s Chapter 5.4 (2015) standard. The three types of waterproofing systems defined by BS8102:2009 ‘Code of Practice for protection of below ground structures against water from the ground’ are:

Type A: This provides a barrier against groundwater and water ingress by surrounding the external walls, floor (and roof) with a waterproof material – literally creating a barrier between water and the structure. This can be applied either internally or externally to the concrete/masonry structure.

Type B: Relies upon the design and materials incorporated into the reinforced concrete structure itself. It is important that all joint detailing is robust and the concrete correctly compacted, as leaks later are very difficult to fix.

Type C: The masonry structure provides the primary resistance to water ingress. Type C systems use a cavity allowing groundwater seepage to reach the drain, while internal surfaces are protected by a cavity drain membrane, with all joints and junctions correctly lapped and sealed. It involves adequately disposing of water, either by gravity, or through a sump and pump to a suitable outlet. This must be designed with adequate access points for servicing and maintenance, and a one-way valve to prevent backflow.

When pumps are required it is recommended that two are installed, alongside battery back-up and alarms, as the cost of flooding, should there be faults or power cuts, outweigh the expenditure and provide peace of mind.

Final words

Given the complexity of waterproofing a building, a design specialist should always be involved as early as possible. Getting the process wrong can lead to the building’s structural integrity being compromised and therefore cost you more in repair and damages later on in the building’s life. Best advice is to get in touch with a waterproofing expert at the earliest stage, which will then leave you free to get on with the exciting bit – the design and decor of your new space.

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