Creating safe and robust waterproofing solutions for structures

Delta Membrane Systems’ Christopher Burbridge explores the challenges and complexities around delivering waterproofing design solutions

The basis of waterproofing structures is to stop water ingress, reduce risk and prolong the lifetime of a structure, whether upgrading existing basement rooms, waterproofing new buildings or converting damp, unused below-ground spaces into dry and habitable rooms. Developments in the industry have delivered a change in how we view structural waterproofing.

The introduction of BIM (Building Information Modelling), for example, has created value in the design process, increasing efficiency within the build process and coordinated project delivery while also driving time and budget savings for building and infrastructure alike. Technical drawings are also vital in visually representing and communicating how a waterproofing system functions or is constructed, and are
a valued tool.

When considering what is best for a certain project there are various options available to designers.

Engage specialists

A waterproofing design specialist provides expertise in structural waterproofing, which is a complex task since every project had its own unique set of challenges.

The specialist should attend site, undertake site investigations, produce reports and manage documentation in relation to the design, ensuring at all stages that sufficient protection is designed into the project. Getting the design correct prior to construction will save significant costs.

The three grades of waterproofing below ground structures

British Standard 8102:2009 (Code of Practice for the Protection of Below Ground Structures against water from the Ground) defines three grades of basement: Grade 1 – basic utility – car parking, plant rooms (excluding electrical equipment) and workshops; Grade 2 – better utility required from Grade 1 – workshops and plant rooms requiring drier environments Grade 3 – habitable – ventilated residential and commercial areas.

The 1990 edition of BS:8102 made reference to Grade 4 (archive storage). This is the same as Grade 3 but with a higher performance level for ventilation, air conditioning or dehumidification.

Available systems

There are three types of structural waterproofing systems available within the UK: Type A Barrier Protection; Type B Structurally Integral Protection; Type C Drained Protection; and finally, Combined Systems.

1. Type A

Type A (Barrier) Protection, often referred to as “Tanking”, provides protection against ground water ingress by application of a waterproof material to the negative (external) walls and structural slab of a basement or underground structure to form a barrier between the structure and any groundwater present.

Type A materials can be applied to either the negative (external) or positive (internal) surface of the wall or floor and also in between wall or floor surfaces. Type
A systems can offer a double layer of protection when applied to both negative and positive surfaces.

Type A materials include: Liquid Applied Membranes, Bonded Sheet Membranes and Cementitious slurries and powders.

2. Type B

Type B (Structurally Integral) Protection is the incorporation of materials to the external shell of the structure itself.

Type B materials include: Reinforced water-resistant concrete or reinforced water-resistant structural steel.

Design, materials and quality of workmanship are paramount when specifying a Type B system due to the pattern of any seepage, poor joints, cracks or other discontinuities such as service penetrations.

3. Type C

Type C (Drained) Protection is the incorporation of a cavity drainage system (internal water management system).

In principle, a Drained Cavity System collects and manages any ground water which breaches the integrity of a structure by managing, collecting and discharging such free water via a suitable evacuation point such as a packaged pump station.

The Cavity Drainage System provides protection to a structure by application of a dimpled High Density Polyethylene (HDPE) membrane, which is applied to the positive (internal) walls and structural slab of a basement or underground structure to form a barrier between the structure and any groundwater present.

A cavity drain system requires minimal preparation and disturbance to an existing substrate.

Type C materials include: Cavity Drain Membranes and Submersible Pump.

4. Combined Systems

Some building warranty providers insist on two forms of waterproofing on projects where they are to provide the building warranty.

Difficult and complex projects may also require combination waterproofing.

British Standard 8102:2009 recommends the consideration for combined systems where the risk is deemed high. A waterproofing design specialist would have the knowledge and understanding of a range of waterproofing systems to provide a robust design based on compatible materials.

As with all waterproofing protections, all rely heavily upon the design and how these materials are incorporated into a project.

Christopher Burbridge is managing director of Delta Membrane Systems