SPECIFIERS: YOUR NEW GUIDE TO LIQUID WATERPROOFING
The versatility of liquid applied systems means they are now a leading solution for both new build and refurbishment projects. Advances in technology has brought new products to market that can be used for a huge variety of applications, including balconies, walkways, green roof terraces, and pedestrian trafficked podium roofs.
With more specifiers now turning to liquids, the LRWA has produced a new go-to guide offering extensive information and advice to assist with developing specifications.
Drawing on more than 40 years’ experience and extensive research, the LRWA’s Design Guide for Specifiers – Liquid Applied Waterproofing Systems for Roof and Balconies – has been produced by the association’s technical committee, comprising representatives from across our membership, including manufacturers, contractors and associate members.
Specification and Installation Best Practice
A large part of the Design Guide is dedicated to providing specifiers with comprehensive guidance on how to correctly select and apply the right liquid products for individual projects. This includes best practice advice on:
- Establishing the performance criteria for liquid systems to ensure a design and specification can be prepared accordingly.
- Design considerations for warm, inverted, cold, green, and blue roofs as well as insulated decks, hybrid roofs, balconies, terraces and walkways.
- Liquid waterproofing applications and the materials that may be used as part of a solution, taking into account their individual performance as well as how they work together as a system.
- Different aspects of workmanship relevant to design and supervision roles.
- Appropriate inspection and maintenance schedules.
The Guide covers the waterproofing of all types of flat roof, balcony and walkway, including associated fittings and construction using systems manufactured by LRWA members. It applies to domestic and non-domestic buildings and focuses primarily on replacement systems for existing roofs requiring a thermal upgrade, product life extension systems for refurbishment projects requiring no thermal upgrade, and new build projects.
Navigating Fire Safety and Performance
Importantly, the Design Guide also references all relevant changes to UK Building regulations following the Grenfell tragedy as well as updates to British Standards relating directly to the flat roofing industry.
One area that is covered extensively is in relation to fire safety requirements and performance.
Guidance on complying with regulatory requirements for fire safety is contained in the following publications:
- In England – Approved Document B, volumes 1 and 2
- In Wales – Approved Document B, volumes 1 and 2
- In Scotland – Technical Handbooks, section 2
- In Northern Ireland – Technical Booklet E
The Design Guide reiterates that fire safety solutions vary from project to project depending on the building type, its use, occupancy, layout, height and construction, as well as the distance from surrounding buildings. Design solutions should take into account the fire performance of individual products and/or complete systems as required.
The Guide goes on to provide specifiers with extensive advice on reaction to fire, fire resistance, and the fire performance of roofs.
It also discusses how the updated fire safety regulations affect the way balconies should be treated. This has raised questions as some of the wording in the amended Building Regulations in England suggests that waterproofing systems comprising combustible material are unacceptable for balconies.
Further clarification is needed on this topic, so the Guide stresses the need to consult the appropriate authorities before setting a brief and considering a design solution. Appropriate authorities could be fire engineers, the local fire service, or the Building Control Body carrying out inspection and approval work.
It is anticipated that the new BS 8579 will clarify the definitions of balcony types, but specifiers are also advised to consider the distinction between a balcony that is outside the building’s thermal envelope and one that forms part of the thermal envelope.
An external amenity space marked as a ‘Balcony’ on an architectural drawing might be over a heated space. In those circumstances, it is part of the thermal envelope (commonly referred to as a roof terrace) and a thermal element in its own right.
As a flat roof, it is subject to all the normal provisions of the Building Regulations, including standards of fire safety and fire spread. Not only that but, as a flat roof, it is not part of the external wall construction, nor is it a ‘specified attachment’ as defined in the amended Building Regulations.
Understanding Thermal Performance Guidance
Many liquid-applied systems can be used as overlays to existing waterproofing on flat roofs. Liquid applied membranes are seamless and fully bond to the substrate making them ideal for use over waterproofing solutions that have reached the end of their design life.
However, it’s important to understand the decision-making process behind whether you can simply choose a liquid applied solution as an overlay to an existing roof, or if it requires a full strip off and a completely new system installation.
We have seen many instances where new materials have been laid on an old waterproofing system, only to find that the roof deck itself has an inherent problem that requires a complete uplift and re-roof – presenting costly and timely rectification.
One aspect which contractors should be aware of is thermal performance. Establishing from the outset whether an existing structure requires a thermal upgrade is vital to determine the scope of the work and whether it will meet Building Regulations.
This is explained in detail in the Guide. In England and Wales for example, replacing more than 50 per cent of an existing roof requires the entire area to be thermally upgraded, as long as it is technically, functionally and economically feasible to do so.
The refurbishment of an existing roof can simply involve the removal and replacement of the waterproofing membrane. Where this work affects at least 50 per cent of the surface area of the individual roof or where it constitutes more than 25 per cent of the entire building envelope – the roof’s thermal performance should be improved.
This can involve a full strip off – replacing the existing insulated roof system to the structural roof deck – meaning a new insulated roof would have to be re-installed to the entire area to meet the current Building Regulations.
However, a partial strip-off involves replacing the waterproofing membrane of a flat roof, meaning it should be thermally upgraded across the whole roof, again to meet Building Regulations.
The comprehensive information in the Design Guide will ensure specifiers provide the best quality waterproofing system for a project. However, they should also take additional steps to ensure it performs to the required standard.
It is essential that the manufacturer’s specification is strictly adhered to as there are so many types of liquid membranes available and each is different.
Specifiers should also verify the performance of a liquid waterproofing product or system via third party certifications, including European Technical Approval (ETA) certificates, BBA certificates and BDA certificates, which are issued by KIWA. These contain data that will confirm whether the waterproofing system will meet specified requirements – as long as the conditions of use are in accordance with the terms of the certificate – and/or satisfy The Building Regulations.
Since European and British Regulations, and product certifications, are under continuous review, the reader should confirm their status with the appropriate institutions before referring to them in specifications.