A Stitch in Time: Replacing the Waterproofing System of a New Build Property

Category: Essential Course

THE PROJECT

The new build property, which contains a retaining wall, is on Grains Road in Shaw, Oldham. Phase one of the project was the addition of a cavity drain membrane (the grey material shown in the photos) and gas protection (the blue material) to the retaining wall and internal divisional walls.

The project had not had the waterproofing detailed before the retaining wall was installed. The developer had missed the National House-Building Council (NHBC) requirement for tanking. A Delta cavity drain system was proposed: AT800, as this is perfect for new build construction and designed to deal with aggressive groundwater ingress and the reported ground gases.

WHY WAS THIS REQUIRED

The client originally acquired planning permission and began the project, which included the retaining wall. It wasn’t until further down the line that the NHBC, which is the UK’s leading provider of warranty and insurance for new homes, enquired about adequate waterproofing measures. This meant that the project had to be reassessed and relevant systems put in place.

Due to the waterproofing and gas membrane having to be added at this stage, the project required three sets of detailed drawings and a change of products. The building had already progressed to the point where it was difficult to carry out even the easiest of tasks, which meant that we had to apply our years of knowledge and expertise to ensure the desired result. Then came issues, as it was a dual system and as the wall had been built, it limited the options available for protection of both gas and waterproofing. The NHCB requirements are for an agreement board certified product, which limited the choice even more.

Instead of a bespoke dual product from Delta, other Delta and Visqueen products were required and a double membrane installation became the only suitable option. This added cost and time to the project. It is also not the preferred option within the industry, which is to install one suitable membrane for both gas and waterproofing.

The moral of the story

The key message to bear in mind here is that you should always plan a project in full before any work commences. The addition of waterproofing and gas membrane systems and the replacement of existing materials was a costly job, which may well not have been the case if everything had been planned in advance. The installation timeframe was also double what it would have been if the optimal choice of waterproofing and gas protection had been incorporated into the project from the start.

Whether you’re a property developer, a homeowner or a landlord on any scale, comprehensive planning is recommended by the British Standards Institution and the NHBC. If you’re ever in doubt, the National Waterproofing Group has members based across the UK who can offer advice, guidance and support to ensure your construction or renovation project runs smoothly and sticks to its budget.

For more information about our waterproofing services and gas membrane installations, contact us on 0800 032 3830 or send an email to robert@prsmanchester.co.uk.