Technical -
Reinforced Concrete

Habitable / Grade 3

What are my options?

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

This page will set out your options for combining systems. At the bottom of the page you will find links to the new BS8102/2022 overview, Ian MacLennan our MD was an author of the new standard so we can ensure compliance with the standard as well as to  NHBC, Premier and third Party warranties and Building regulations.

The British Standard BS8102/2022 says you have to consider 2 forms of waterproofing if the risk of a leak is high, or the consequences of a leak are unacceptable. Insurance companies will insist that you employ 2 forms of waterproofing and that the system is designed by a CSSW qualified designer with suitable experience.


MacLennan do not use or recommend concrete additives for your concrete construction because concrete is watertight without additives.. Water can only come through a concrete structure where there are cracks or defects.

Additives do not prevent cracks and defects. If you have a crack or a defect they will not have any benefit from additives as the additives do not fill the defects and are not present in the defects.

The engineer and the waterproofing specialist should agree on crack control. Crack control will prevent water ingress.



Movement Joints

BS8102/ 2022 says movement joints should be designed out where possible. If they are unavoidable then they should be designed by the waterproofing specialist in agreement with the engineer.. Not the manufacturer. The manufacturer would not accept any design liability.


Service Entries

BS8102 /2022   says Service entry ports should be designed out where possible as they are difficult to waterproof.  MacLennan do have gasket systems for service entry ports that can be designed for the services required and guaranteed for 10 years.

BS8102/2022 is very clear that you must consider form and feasibility of repair of the waterproofing after construction is complete including finishes. For this reason MacLennan do always recommend serviceable hoses in all joints.

If you build the basement with poured concrete following the relevant codes as sighted in BS8102 Paragraph 9 ( This should be the responsibility of the waterproofing designer and engineer ) You will have a watertight structure which can be made compliant with the application of Crystal coat. Crystal coat will repair and minor defects ( unlike additives ) You will have what is agreed to be a Type B basement and it complies with Third party warranty companies and BS8102 requirements.

If the basement is to be habitable or have finishes or internal walls then you must have a second form of waterproofing which can be repaired in the event of any issues. It is a requirement of BS8102/2022 that the basement waterproofing is repairable. This means you will need a type C system which is repairable and serviceable.

Servicing is a huge benefit to the client and protects the design team because unlike with every other waterproofing system , a serviced system can prevent leaks before they occur. It also keeps the client in touch with the designer and installer of the system so any issues can be prevented and dealt with under guarantee. No other systems provide that benefit.

External Systems

If you have a problem with gas or you require 3 forms of waterproofing you may need an external system.

However You cannot rely on external membranes on their own, It is proven in law ( Outwing case 1990 ) and accepted in the industry that type A external waterproofing cannot be installed defect free.

All codes of practice and insurance companies require designers to consider the form and feasibility of repair in the event of a leak. You cannot repair an external system.

External systems are very weather dependant and you can suffer long delays to your programme if the weather is cold or wet.

External systems need additional site controls and protection as they are prone to being damaged by follow on trades and site processes as well as ground settlement.

This is why MacLennan will always install a cavity drain system,  and only recommend Type A if gas mitigation is required.



Basement Design

If you are building a basement for accommodation or recreation, or storage of plant, paper, or anything sensitive to moisture you are required to achieve a Grade 3 environment to comply with BS8102/2022 the British Standard for earth retaining structures

If there is a high-risk of a leak, such as in a high water table, or if building a basement where the consequence of a leak is unacceptable, then you should have 2 forms of waterproofing. External waterproofing is difficult and sometimes impossible in piled construction.

External waterproofing cannot be installed in inclement weather and can effect programmes for weeks on end in poor weather.

Find out more about External Waterproofing

Get in touch with our technical team today!

First / Primary Form of Waterproofing

The concrete box forming the basement should be well constructed with correctly placed hydrophilic strips or, better still:  injectable hoses which can be repaired.

We recommend the use of additional joint detailing and crystalline slurries to create a type B watertight structure.

The water bar we recommend is fully serviceable and comes as a hollow hose wrapped with hydrophilic material. In the event of a leak, the hose can be filled with acrylic resin or Polyurethane, or even cement grout to repair defects in the concrete structure such as cracks, shrinkage voids, or honeycombing. All of which are common and sometimes unavoidable in concrete placement in normal site conditions.

A concrete structure without waterproof additives that is well compacted, isn't honeycombed and has well prepared and detailed joins with water bars, will provide a Type B structure. Crack control can be employed by the engineers to provide additional waterproof properties to the construction if required.

an image showing a Waterbar as described
A typical Waterbar

Service Entries

Service entries need to be well designed to ensure that they are watertight but can also be easily remedied in the event of damage externally.

To this end, pipes and cables should be separated by 20mm and come through the entry in a manner where they are supported but can be moved within the duct for remediation with resin filler if required.

Find out more about Service Entries

Waterproofing Concrete with Crystalline Slurry

Crystal Coat is a concrete waterproofing system applied to the concrete after it is poured and the form-work is struck.

Concrete additives are commonly applied to the concrete mix before it is poured. This means that when concrete cracks or becomes damaged and results in water ingress, the additives are of no benefit. MacLennan use Crystal Coat to waterproof concrete as the system is applied once the concrete has set but is normally still green. Crystal Coat is absorbed into the concrete and reacts with free lime to repair the defects by effectively filling them, providing a once again waterproof structure.

This system is effective, proven and acceptable to all major insurers.

Crystal Coat for waterproofing concrete is less expensive and more effective than additives, and provides the first part of the MacLennan fully insurance backed guaranteed waterproofing system.

Find out more about Concrete Waterproofing

Crystal Coat Application for Waterproofing Concrete
Crystal Coat Application for Waterproofing Concrete

Second Form of Waterproofing

From a design point of view Type C is mandatory to comply with BS 8102 2009 for a habitable basement.

Type C waterproofing is a cavity drain, often in the form of a plastic membrane with drainage that is built into the structure behind walls or linings.

It is essential that drainage is reliable or that the system is pumped. The pump design is critical.

It is the most effective form of waterproofing for cobvious reasons. If the waterproofing system leaks for any reason, you have to be able to resolve the problem with minimal disruption to the occupier. You cannot do this with A or B systems.

The cavity drain system is now favoured by all insurers and used by all reputable designers because industry professionals are aware of the issues associated with external membranes and concrete additives.

The system is not designed to allow water in and then manage it. The basement is built as watertight as possible (1st form of waterproofing) , however as the industry knows, it is difficult to guarantee a successful watertight basement construction in normal site conditions. The cavity drain is installed as the serviceable, repairable and guaranteed waterproofing system which then ensures compliance with insurers and British Standard requirements.

Find out more about Cavity Drain Systems

Cavity Membrane Installation
Cavity Membrane Installation

Ground Gas

MacLennan Radon gas design detail
MacLennan Radon gas design detail

Before building a basement, ground gas has to be taken into consideration.

If testing proves thatf Radon, CO2 or Methane are present then the basement has to be designed so that the gas cannot enter the basement structure.

This can be achieved with the waterproofing system.


Deck & Roof Waterproofing

If the basement is not completely covered by the house above, as is often the case, then you will have a deck or roof  to waterproof.

The deck waterproofing should always be carried out by the same waterproofing specialists who waterproof the basement, as the detailing between the two is critical and split responsibility should be avoided at all costs.

In the last few years, deck waterproofing has moved  away from single ply membranes and felt which have a history of failure due to the numerous laps, joins and seams.

The industry is moving towards, seamless, fully bonded, elastomeric applied systems such as Polyurea and Polyurethane.

Finishes on decks include green roofing and hard landscaping or even driveways and parking areas.

Due to the large number of products with different properties available on the market, the deck/roof waterproofing should be specified by the waterproofing specialist and the work guaranteed and insured for design, supply and installation by the same company.

The Waterproofing Company

The minimum requirement for a waterproofing specialist is:

  • Design, supply and install all waterproofing systems. No split responsibility.
  • Take full responsibility for waterproofing Basement walls, floor and roof.
  • Accept design liability and have Professional Indemnity insurance for waterproofing of 10 million (unlike any manufacturer).
  • Give insurance backed warranty of up to 10 years that covers supply and installation.
  • Comply with all relevant health and safety requirements.
  • Do not use sub-contractors for specialist work, only their own fully trained staff.
  • Must be able to provide references for numerous similar projects.
  • Be able to accommodate project time constraints.

Unfortunately local authority building inspectors only ask for BBA certification for materials and systems. This does not provide any guarantee that the work will be carried out correctly or give any protection to the client.

Waterproofing is wholly reliant on expert design by the waterproofing contractor and installation by very experienced technicians. Waterproofing is so often carried out by ground workers and builders taking advice from manufacturers sales personnel, and this is the main reason for failure.

In the event of a claim. A manufacturer warranty will not cover the installation




Reinforced Concrete - Technical Download Area

Included in our Technical Download Area:

Specification sheets

Data Sheets

3D Details

Product Details

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