Bernard Cvijanovic, Technical Service Director for GCP Applied Technologies, Europe shares key considerations when selecting protective membranes for safe and secure belowground structure

Odourless and invisible but very much a hazard, ground gases can present serious challenges for underground building and construction projects. Toxic, asphyxiating or explosive gases such as methane, carbon dioxide and radon may be present in the ground naturally, or from contamination and a build-up of these gases can have dangerous implications.

When it comes to constructing safe and secure buildings, preventing the transmission of gases is critical. It is therefore essential to specify protective solutions that comply with national standards to ensure that they work properly and safely, so that finished buildings pose no threat to human life.

The British Standards Institution (BSI) is an independent organization established in 1901 as the world’s first standards body. Recognized globally and operating in 193 countries today, construction engineers, architects, design consultants and regulators around the world consult BSI guidelines when assessing and approving structural designs.

In 2015, BSI updated its code of practice for gas resistance systems, introducing more stringent standards. The updated standard, BS 8485:20151 , stipulates a certain gas resistance score depending on the hazard present on site and building type. A combination of three protection measures can be used to achieve the score: structural barrier, ventilation and gas resistant membranes.

As a result, many manufacturers have since had to introduce new products and solutions as well as new application processes such as lap welding in order to meet the stricter standards. Consequently, in some cases protecting new buildings against natural gas leaks has become more time-consuming and costly.

A vast majority of gas resistant sheet applied membranes in the UK require lap welding, adding complexity that includes additional safety measures, more labour and equipment, and increased logistics planning. Designing and installing a ventilation system to release gas build-up, also adds labour, equipment and logistics complexity. Both options extend project timelines and increase costs.

New build projects need reliable protection against another major natural element too: water. In the UK, this means design engineers and architects must choose yet another protective measure to satisfy below ground waterproofing codes and requirements. The good news is there is a time and cost efficient alternative to choosing and installing a waterproofing membrane plus a gas resistant membrane that does not require welding.

1BS 8485:2015 Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings, published by BSI, June 2015

Waterproofing and gas resistance in one

Owing to innovative and forward thinking technology behind one of their leading products, GCP Applied Technologies’ PREPRUFE® 300R PLUS LT membrane with ZIPLAP™ adhesive-to-adhesive technology provides both waterproofing and gas resistance to below ground structures.

If protecting a basement as Grade 3, PREPRUFE® 300R PLUS LT membrane enables designers to obtain 2 points as a gas barrier and 2.5 points as a structural barrier as per BS 8485:2015 Table 7 and Table 5.

Changes to gas permeability standards

Non-profit organization CIRIA first introduced CIRIA C665: ‘gas screening value’ calculations and characterization of sites between 1 and 6. BS 8485:2007 developed this to include types of building i.e. receptor sensitivity. The two parameters considered for a gas hazard assessment are characteristic gas situation and building type.

In June 2015, the BS 8485:2007 standard was significantly revised and expanded to become
BS 8485:2015.


BSI’s gas resistance standard today: BS 8485:2015

What you need to know

BS 8485:2015 outlines stricter guidelines on permeability levels for membranes, to prevent the entry of hazardous gases into new buildings. In addition, it lays out a more detailed design process, one similar to The Code of Practice for Protection of Belowground Structures Against Water from the Ground (Section 7.2.4 of BS 8485:2015). The standard declares “A methane gas transmission rate of <40.0 ml/day/m2/atm (average) for sheet and joints (tested in accordance with the manometric method in BS ISO 15105-1) is usually considered sufficient.”
Question your choices

Since the BSI announced the revision to the BS8485 standard, many manufacturers have been scrambling to adjust to the stricter guidelines and update their existing inventories to meet the current guidelines. This means there is still some confusion within the construction industry around which systems are compliant or not. Builders, architects, engineers and designers need to be certain there is no ambiguity regarding permeability levels for membranes. Independent test results as well as certification from manufacturers to confirm accuracy should be requested.

A proven solution

GCP Applied Technologies’ Preprufe® 300R PLUS LT waterproofing membrane has achieved BBA certification confirming acceptance that the certified product satisfies the BSI’s strict new guidelines for gas resistance.

PREPRUFE® 300R PLUS LT waterproofing system offers not only excellent waterproofing performance, but also provides certified protection for below ground structures against the harmful effects of methane, carbon dioxide and radon.

With a proven 25-year track record, the PREPRUFE® 300R system may be better known globally for its waterproofing performance on commercial, industrial and residential buildings. Recent tests by accredited external labs2 have demonstrated to the satisfaction of the BBA that the PREPRUFE® 300R PLUS LT system’s permeability level for methane, carbon dioxide and radon ground gases meets the current British Standards Institution (BSI) guidelines. This means engineers and architects can specify the PREPRUFE® 300R PLUS LT system to waterproof below ground structures with the added value and peace of mind that they are meeting the stricter gas resistance guidelines without changing their design to add ventilation or welding. And, builders and applicators can continue to use and install the PREPRUFE® 300 PLUS LT membrane product in the same way they always have.

2Independent Test certificates of KIWA 1.1/24606/0315.0.2-2017e and 1.1/24606/0329.0.2-2017e dated 19.09.2017.

Making the grade

With the introduction of BS 8485:2015, there should be no ambiguity regarding permeability levels for protective membranes. When it comes to complying with national standards, and meeting the requirements needed to build safe, insurable buildings, independent certification and third party results are key.
Customers need to be sure that manufacturers’ claims are credible. The best way to do this is to seek accreditation from an external lab and independent certification that manufacturers’ products live up to their claims.

It is essential to test all aspects of how a product is applied, including the over laps which are generally most vulnerable to leaking gas and water but often overlooked. This is where bonding technology is essential to achieve acceptable standards of protection. GCP’s PREPRUFE® 300R PLUS LT system features a patented ZIPLAP™ adhesive-to-adhesive technology that lives up to the task, eliminating the need to rely on welding or tapes to seal laps.

Eliminating the need for welding

In light of the new guidelines, many manufacturers of protective coatings whose products were previously applied using the traditional taping process have been forced to introduce welding at the laps confirming that a gas resistant bond is achieved in order to meet the new standard. This welding adds complications to the installation process, causing projects to take longer with increased risks. The varying degrees of experience welders have on a job site can further complicate the process and the long-term effectiveness of the laps to resist gases.
If carried out properly and to high standard, welding is a good system and provides efficient gas protection. However, the challenge with this is that construction companies require installers with a specialised Level 2 NVQ qualification in gas resistance to carry out the welding safely and effectively. There are not many Level 2 NVQ certified installers in the UK market and even if there were, it is another aspect to consider on a project, as it requires additional training costs, as well as adding time to the project for the welding. The welding process can also be extra-challenging if the profile isn’t flat, which is often the case in underground structures. The verification process is also more time-consuming as the gas inspector needs to check all of the welding too.

Many technologies will require onsite welding in order to comply with the BS 8485:2015 requirements of methane and carbon dioxide transmission. Unlike any other product currently on the market, PREPRUFE® 300R PLUS LT membrane is unique with its patented ZIPLAP™ adhesive-to-adhesive technology that seals laps completely. Owing to ZIPLAP® technology, there is no need for onsite welding. The ZIPLAP™ technology provides quick and easy application and is adhesive on both sides of the lap providing an extra strong bond.

Added value

In addition to providing certified protection for below ground structures against harmful gases GCP’s PREPRUFE® 300R PLUS LT waterproofing membrane with their patented ADVANCED BOND TECHNOLOGY™ system is applied directly to concrete creating a full bond with the structure to protect it against the harmful effect of water and corrosive soil. This unique bonding technology is unlike other waterproofing membranes that require a fleece-like porous material between the membrane and concrete leaving the structure susceptible to lateral water migration.

Using PREPRUFE® 300R PLUS LT system with ADVANCED BOND TECHNOLOGY™ and ZIPLAP™ technology means a much lower risk of failing gas resistance tests once a building is completed.

BS 8485:2015 highlights protection from methane and carbon dioxide in particular, but also provides guidelines for protection from another potentially toxic gas – radon. In the open air, radon causes no problems, but it can seep into buildings through cracks and holes in the foundations, where it can build up to dangerous levels and become toxic.

Providing effective gas resistance is of paramount importance to reduce the risk to human life in the construction of new commercial, industrial and residential buildings. For peace of mind, it’s always best to opt for a product that has a successful track record and standardised certification to prove it works. By selecting a combined waterproofing and gas resistant product that doesn’t require welding, like the PREPRUFE® 300R LT PLUS membrane, construction companies can save time, as well as achieve a robust seal for long-term protection. Recognised as one of the most advanced and unique waterproofing solutions for below ground structures, the PREPRUFE® PLUS system, featuring a durable HDPE geo-membrane, provides a protective barrier for the life of a structure.

For more information visit:
GCP Applied Technologies

Call Now Button