When you are constructing underground structures, it can sometimes be necessary to protect against both water and gas. This may require you to take another look at the construction methodology and the waterproofing strategy but it is certainly possible to produce a gas proof and waterproof underground structure.
What is BS8102:2009 and BS8485:2015?
The primary purpose of the British Standard BS8102:2009 is to control the ingress of water into an underground structure. Similarly, the purpose of the BS8485:2015 is to prevent gas penetration. however, waterproofing and gas proofing are very much intertwined. For instance, structural waterproofing designs that are in accordance with BS8102:2009 can, in fact, be sufficient for certain gas situations in certain building types.
The BS8485:2015 provides the regulations concerned with ground classification, building types and gas proofing design. If a site has an issue with gas or hydrocarbons in the ground it will be given a Characteristic Situation score according to how severe the gas flow from the ground is.
Basements which need to be gas proof and watertight needn’t be any more complex to deliver; when interpreting BS8012:2009 and BS8485:2015 together, the waterproofing designer will be able to design a waterproofing system which achieves all requirements.
All sites characterised with a gas situation must prevent the buildup of gasses against the structure. This is achieved by providing pressure relief in the form of stone trenches, geotextile blankets or active dispersal systems. Similarly, structural waterproofing designs must dissipate the build-up of water against the structure in high-risk situations with high water tables.
There are many different pile types and construction methods and some construction methods support gas proofing and structural waterproofing than others.
Certainly, for some lower grade basements, a welded sheet pile wall can be sufficient for gas proofing and waterproofing, however, most basements will require a gas protection and water protection barrier.
Secant walls only provide some structural waterproofing protection and walls constructed from waterproof concrete definitely provide a waterproof barrier to some degree. There is one sure way of meeting the requirements of both BS8102:2009 and BS8485:2015 and that is to use a fully certified membrane. A fully certified structural waterproofing and gas resistant membrane will protect against ground gasses as well as protecting against hydrostatic water pressure.
Whilst a membrane which meets the requirements of both British Standards is indeed a solution, it is never good practice to rely on one form of defence, especially on high risk sites. These high risk sites are characterised as such often due to high water tables and hydrostatic pressure.
For theses instances, combined protection is recommended by BS8102:2009 and is a requirement for all NHBC guaranteed buildings. Combined protection can be achieved by using two forms of barrier defence; Type A barriers, Type B barriers and Type C barriers can be combined, as required, to achieve a combined protection for an underground structure.
FIS Products provide innovative solutions for both the construction, structural waterproofing and gas protection markets. Providing detailed and infallible support for Architects, Engineers, Basement Designers and Contractors alike, FIS are market leaders in high quality solutions for structural gas and water protection.
The Premcrete Combi-Seal is a new membrane which is capable of gas proofing and waterproofing a basement. Premcrete have produced a membrane which combines a waterproofing membrane and a gas protection barrier and this membrane is the first in the UK to comply with the BS8485:2015 with a gas transmission rate of >40ml/day/m2/atm. The membrane is independently certified and approved and it comes with a 25 Year performance warranty.
With our extensive experience, we are able to provide implicit advice and our CSSW qualified technical designers can provide practicable working detail drawings, in addition to this, we carry £10M Professional Indemnity Insurance which allows us to take responsibility for the designs and the technical advice which we produce. As an organisation, we believe a good structural waterproofing strategy must consist of multiple forms of structural waterproofing protection, a qualified designer, a comprehensive set of warranties covering the design, product and installation and a detailed quality control plan for the installation phase.
If you have a project which requires gas proofing and structural waterproofing, why not give us a call, we’ll be glad to discuss the design and help you to make it compliant and practicable.