Type A Waterproofing

Type A waterproofing protection is defined by BS8102:2022 (Code of Practice for Protection of Below Ground Structures Against Water from the Ground) as ‘barrier protection’. This is where a material is put in place that offers a barrier to the passage of water, with the aim of keeping the target environment within a prescribed level of ‘dryness’.

These barriers can be placed either inside, outside or within the structure. Each of these positions has its own considerations.

DOWNLOAD - Best Practice Guidance: Type A Waterproofing Systems

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Types of barriers used

There is a wide range of products used for Type A waterproofing. These roughly fall into seven distinct categories according to product type, form and application as follows:

Bonded sheet membranes
Bentonite clay active membranes
Liquid-applied membranes
Mastic asphalt membranes
Cementitious crystallisation active systems
Proprietary cementitious multicoat renders, toppings and coatings
Loose Laid Membrane systems

Other types of Waterproofing (B & C) >>

Effectiveness of Type A Waterproofing systems

The water tightness of a Type-A system relies fundamentally on the effectiveness of the waterproofing system, its preparation, application and the structure. With a high-water table, any defects in the waterproofing barrier could allow water to penetrate and if the structural elements are permeable (e.g. masonry), this will allow free water to enter the basement, cellar or underground structure. If this water is not removed, the underground structure will fill to the level of the water table. Structural elements that are less permeable, e.g. concrete walls which resist or lessen the occurrence of free water, can extend the usage of Type A construction.

Since fundamental reliance is placed on the waterproofing system in Type A systems, account must be taken of the need to gain access if a defect occurs, along with the correct product selection to ensure any materials satisfy the requirements of their intended purpose (robustness, protection requirements, self-healing etc.).

External & Internal Type A Systems

Externally applied type A systems may require subsequent excavation. However, locating the source of a defect in a system not continuously bonded to the substrate wall can be difficult. An internal system can make accessing and remediating the defect more straightforward, but consideration needs to be given to internal fittings, the location of any load bearing/structural elements and if the structure is playing a part in the supporting of the waterproofing system.

PCA - Type A Waterproofing

Situation when you may/maynot consider Type A

As previously mentioned there are various types of type A systems as a result type A waterproofing can be very versatile however choice of product will be restricted by the stage it is installed, the substrate it is being applied to, and weather access is available to the external side of the structure.

Consideration towards the water tables

With a varying water table, significant water ingress through defects will occur only during storm or water-logged conditions and again, will depend on the resistance of the structural elements. If the water table is high only briefly, the ingress might not be enough to show itself. The longer it stays high, the greater the risk of significant water ingress.

The incorporation of maintainable land drains can be used under appropriate ground conditions to achieve a situation where all moisture is under capillary action. Scheduled routine maintenance of land drains is essential. Lack of proper maintainable drainage to basement surrounds may result in hydrostatic pressure and subsequent leakage if there are any defects in the waterproofing or concrete.

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The designer has a critical role to play too

Since reliance has often to be placed on the waterproofing system, the waterproofing designer must ensure that the materials are properly selected and adequate for the proposed location and conditions. It is imperative that all continuous horizontal, sloping or vertical waterproofing be specified, and executed, in one proprietary waterproofing system. Consideration should also be given to the scope of where products are sourced, as supply from differing sources can lead to complications when trying to identify a root cause of possible failure.

With ALL types of waterproofing it should be stressed that it is rarely the material, but the detailing / installation / lack of care that fails. Avoid complicated shapes - keep internal / external corners, movement / expansion joints and penetrations etc. to a minimum. External 90 degree angles should have rounded corners and internal corners should be filleted.

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Waterproofing design - important requirements to consider

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Type A Waterproofing to Existing Structures

Many of the considerations applicable to structural waterproofing design in new construction, apply equally to the design of systems for existing structures. However, contrary to new-build scenarios, there are limitations when working within the confines of an existing structure. There is typically a limited opportunity or scope to make structural alterations for the purpose of installing a given system.

Additionally, (in the case of new construction waterproofing), the designer is providing the initial or first-stage measures of protection against water ingress/groundwater. In existing structures, it is often the case that designs are provided for the purpose of remedying failures in those initial measures, to address problems with systems of considerable age in older or historic property, or to facilitate change of use.

If options are limited by the confines of the structure, it is important to understand what that structure is, and equally, the nature of any installed waterproofing measures within it which may further influence design.

Thorough waterproofing inspection is key

Prior to going ahead with any type A waterproofing to a building, an analysis through visual inspection, inspection of drawings (where available) and potentially intrusive investigation (i.e. trial hole formation) should be undertaken along with a thorough understanding of the structure and how it is constructed is developed. The effects of any structural discontinuity as may typically occur in an existing structure must also be assessed.

Once the structure is understood and objectives and instructions are defined, it is then the role of the Waterproofing Design Specialist to configure products and systems within that structure all while considering the appropriate factors detailed within this guide, so that the objectives are successfully met and structures are protected in the long term.

Type A Waterproofing Doc >>

Type B Waterproofing

Type B protection is where the structure itself is constructed as an integral water resistant shell. This relies heavily on the design and materials incorporated into the external shell of the structure, as well as the quality of the workmanship contributes to the success of Type B Systems.

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Type C Waterproofing

Type C protection has become the most common form of waterproofing system used in retrofit, existing basements and within new build basements. It allows moisture or running water to penetrate through the external wall or floor of the structure and to travel behind a cavity wall membrane to a drainage system and sump pump/pumping station.

More about Type C Waterproofing >>

Training courses that might be of interest

Want to learn more about structural waterproofing

For those interested in learning more about structural waterproofing and BS8102 requirements; there is a variety of PCA training options for surveying professionals as well as technical/trade professionals.

Use the search tool below to find available waterproofing related training courses or simply go to our training & qualifications section. Alternatively, if you want to chat to someone, contract our training team on 01480 400 000 or contact them online.

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More about PCA Membership

Interested in taking part in the CPD scheme but you are not a PCA member? Find out more about membership and why it will benefit you!

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More about Structural Waterproofing

Guidance and information regarding structural waterproofing for professional construction or property specialists

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Type A waterproofing

Type A Waterproofing

DOWNLOAD - Best Practice Guidance: Type A Waterproofing Systems

Types of barriers used

Effectiveness of Type A Waterproofing systems

External & Internal Type A Systems

Situation when you may/maynot consider Type A

Consideration towards the water tables

The designer has a critical role to play too

Waterproofing design - important requirements to consider

Type A Waterproofing to Existing Structures

Thorough waterproofing inspection is key

Type B Waterproofing

Type C Waterproofing

Want to learn more about structural waterproofing

More about PCA Membership

More about Structural Waterproofing

Other Relevant Information