Waterproofing Commercial Buildings


A commercial basement is usually a large underground space with a mixture of parking, storage and habitable spaces, so it's important these areas be kept free from water. MacLennan have worked on an array of commercial projects including office blocks, hotels, shopping centres and leisure centres.

The design of a commercial basement, like with all basements, is critical but can be more challenging because of the mixed-use and often over several levels.

MacLennan has successfully designed, managed and delivered hundreds of commercial waterproofing contracts up to £2.6 million for a single waterproofing package and so have industry-leading experience in this type of basement project.

We discuss some of the key points to consider in the pages  below.

What construction type are you waterproofing?

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Waterproofing Commercial Basements - Key Points

The Delivery

Commercial basements are usually very large in size, can be complicated structures, and are often built in phases or over a long period of time.

This makes planning, communication and quality control absolutely critical.

MacLennan closely manage the project to ensure every phase is set-up and delivered with minimum risk and full control over the quality of the installation of the waterproofing solution.

Starting with a quality plan, including:

  • A program of works
  • Technical data sheets
  • Inspection and resting plan
  • Builders work in connection documents (to clarify preparation and work others)
  • Regular attendances
  • Project management to successfully deliver any size and type of commercial project


Large New Build Basement

Basement Design

Building Warranty providers will insist on a CSSW qualified designer.

The MacLennan design team are all CSSW certified and most are also WDS qualified (Waterproofing Design Specialist).

More importantly, they are all hugely experienced in specifying basement waterproof systems and managing large commercial contracts.

The options for waterproofing a concrete commercial basement are external waterproofing, waterproof concrete, or a cavity drain system.

When constructing a commercial basement structure that is intended for accommodation, recreation, or retail with parking, you are required to comply with BS8102 under British Standards.

For all earth retaining structures, the correct basement grade must be applied.

In order to comply with British Standards, if the risk of leak if high, such as in a high water-table, or if building a basement where the consequence of a leak is unacceptable, then you should install 2 forms of waterproofing. The consequence of a leak in a commercial area other than a car park can be disastrous so you should always have 2 forms of waterproofing.

All codes of practice and insurance companies require designers to consider form and feasibility of repair in the event of a leak.

Find out more about our Waterproofing Design Team

BS8102 4.3.2.

Contingency planning for dealing with any localised defects or system failure that arise should be included as part of the overall water-resisting design for the structure.

MacLennan will always install a cavity drain and either Type A if gas mitigation is required, or Type B Crystal Coat if there aren’t any gas issues. It is the only way to comply with standards and deliver a risk-free basement waterproofing system.

Find out how to comply with BS8102.

Why should I work with MacLennan?


We Design, supply and install. There's no split responsibility with MacLennan.


MacLennan live and breathe waterproofing, have a look at one of our free CPD seminars and find out!


MacLennan has the most comprehensive guarantees and insurances in the industry.

What are other things to consider?

Single owner responsible for ongoing maintenance.

Is the space and waterproofing a single or multiple system?  All systems should be designed independently if having multi- owners in the future. This will mean independent systems forming a whole solution.

Fire breaks & partitioning and the effect on design.

Considering fire breaks or partitioning if the areas are separated internally, as this requires a slightly different detailing.

Future Proofing the waterproofing strategy and change of use.

A car park or plant room today could be office space or commercial space in years to come.

Considering the implications of Grade 2 waterproofing.

If an area is to be better utilised, then it would be deemed Grade 2 under BS8102. However, the consequence of a leak would still be unacceptable so you should use 2 forms of waterproofing and a fully serviceable system unless the client specifically instructs that a leak is tolerable and worth the risk, and they have had suitable qualified advice to that effect from their own team. If this is not confirmed and there is a leak due to reducing the waterproofing for Grade 2, the client could argue that it is a design team issue due to the client's lack of expertise to understand the consequences of their cost over risk decision.

Is the first phase of works to build the shell including the waterproofing strategy connected to the future fit out sub-contracts?

The spaces might be sold on to clients to fit out the internals themselves, this sometimes splits the walls and floors packages, This often happens with retail and restaurant spaces as an example. This can lead to split liability and responsibility so in the event of a leak the client and or the design team or teams can suffer huge financial loss and disruption.

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