Volatile waterproofing design
Guest blogs are always warmly welcomed and often provide an alternative viewpoint. This time around, we hear from PCA member Dave Cook, Cook Group Ltd, as he discusses the importance of applying standards from the outset of a project and walks us through what each of these guidance documents tells us, particularly when Hydrocarbons or VOCs (volatile organic compounds) are involved....
Dave's thoughts on the issue...
In my opinion, the structural waterproofing industry and the ground gas ‘property level’ protection industry, whether intentional or not, has long been a case of 'never the twain shall meet' for the majority of manufacturers, installers, engineers, architects and main contractors. There’s a lot more awareness now than there has ever been, as demonstrated in our BS8102: 2022 bible with reference to BS8485: 2015 +A1 2019, Bre report 211, various Ciria guides and the Basement Information Centre's (TBIC) waterproofing document and website.
The mindset is that a well-designed Grade 3 basement, excluding cavity drainage systems (with 1 exception), gives you 4 points in BS8485 and that makes all the possible design problems go away! So, what’s the issue? Well, there are no particular problems if the issue is carbon dioxide, methane and radon. We’re pretty much covered and ‘the system works’.
Where it unravels - Hydrocarbons & VOC’s
Where it starts to unravel is when Hydrocarbons or VOCs are involved. Think for a minute as to what the acronym VOC stands for - Volatile Organic Compounds. That first word ‘Volatile’ may be the first warning sign? The majority of VOCs and Hydrocarbons are proven to be carcinogens that can cause birth defects in unborn children and other life limiting illnesses. You may be thinking: “Not to worry if hydrocarbons or VOCs are mentioned. I’ll just upgrade my spec to a hydrocarbon membrane." If only it was that simple...and that’s just your first mistake!
Standards, guidance & good design
Let’s roll it back to what all good designers should do - which is to apply the relevant standards and guidance at the beginning. As an example, let's look at some of the points within these documents that should be considered:
- BS8485:2015 + A1 2019: BS8485 is a standard that gives definitive guidance to protect against Carbon Dioxide and Methane on new build structures (nothing else!). Appendix H however, gives an insight into what you ought to consider in relation to VOC’s. It tells the designer to be very careful by giving due consideration to the source and pathway before we even start thinking about specifying a hydrocarbon membrane. The source is where the contamination is located and how much of it there is. The pathway is how it’s going to move to your occupants (the receptor) in that shiny new basement you’re designing.
- BS8102:2022: We’ve had a selection of the nation’s finest rework BS8102. It’s barely a year old. With regard to ground gases though, it tells us to look at BS8485, the TBIC basement waterproofing document and Bre Report 211.
- Bre Report 211:2023: This report focuses solely on Radon with no mention of VOC’s / Hydrocarbons...and in my opinion, quite rightly too. Incidentally, this has just been reviewed and updated.
- TBIC Basement waterproofing guide: The guidance document and the TBIC website give detailed information about Carbon dioxide and Methane, but for VOC’s, refer you to three Ciria guides - C682, C716, and C748. All of these provide direct guidance to the waterproofing designer.
- Ciria Guides C682 (The VOC’s Handbook),C716 (Remediating and mitigating risks from volatile organic compound (VOC) vapours from land affected by contamination) and C748 (Guidance on the use of plastic membranes as VOC vapour barriers). These guides are very clear. There isn’t a VOC or Hydrocarbon membrane on the market which is 100% VOC or hydrocarbon vapour proof. VOC and Hydrocarbon membranes are there to mitigate the amount of VOC or hydrocarbon vapours that will transfer into the proposed living space over the proposed lifespan of the building, down to an acceptable level that the Environment Agency tells us will do no harm to the occupants (receptors).
But what do these standards and all their cross-referencing tell us? And, most importantly...how does that transfer to what a waterproofing designer actually needs to know before they put their professional indemnity (PI) design insurance on the block?
Considerations for a Hydrocarbon / VOC resistant Waterproofing design?
The general norm for design managers and architects is to trawl the internet, find a manufacturer's standard details and make contact. Immediately there are lots of recommendations from a sales rep gleefully rubbing their hands together for product X or product Y and between the manufacturers, available in all colours of the rainbow and with magnificent claims that their membrane is a 'one stop shop' for all VOC’s. Now, I might sound a little cynical with regards to these claims here, but you might find yourself in a pot of something at the end of that rainbow and it might not be gold!
Salient points from the Ciria guides for the waterproofing designer are as follows:
- C682 very simply tells you to consider that VOC’s will move in groundwater
- C716 gives some guidance on the type of membrane you might be considering i.e., HDPE, LDPE, polypropylene
- C748 gives very specific guidance on the type of product you can use and methods of jointing the membrane, in relation to the Challenge 9 testing regime; such as Sodium Bentonite membranes are not suitable or membranes <0.5mm thickness (excluding any bonded fleece)
Other considerations...
Along with the above, you need to consider puncture resistance and durability of the system you propose to install. How do you propose to join and detail the membrane? Is your proposed membrane weldable? Will your membrane be subject to tensile loading? Will there be a risk of damage from follow-on trades? Has the site been remediated to a point where your proposed specification will effectively deal with any residual contamination?
C748 tells us that a VOC membrane should be tested to the standards as set out in BS EN 14414 test method C. It also tells you that you should request this information from your proposed manufacturer so that it can be given to the regulator for their approval (not yours or your sales rep).
Most importantly of all though....do you have the knowledge and qualifications to make these judgement calls? Holding the CSSW qualification does not necessarily make you qualified and equally, does your proposed manufacturer have the relevant knowledge and qualifications to advise you?
2 Forms of Waterproofing
We know we need two forms of waterproofing for the majority of projects. Are you going to specify a Type A VOC barrier to tick that box and then put a Type C system internally? If so...you’re a braver person than I am if you were going to do that!
Hydrocarbons and VOCs are transient, i.e, they will dissolve in water or the particle sizes can be so small that they will move in water (remember Ciria C682 tells us that in graphic detail). This then leads to potentially VOC contaminated water to sit in channels behind a bit of studwork or an internal framing system potentially for months on end to evaporate and permeate into the living space? Remember some Hydrocarbons and VOCs will dissolve butyl taping systems in seconds. A very diluted solution to be fair may take a couple of months to undo all your tape work!
Let’s not forget that this blog just touches on the subject. There is so much more that you as the designer need to consider.
Key takeaway - do your research!
To close off this blog, the biggist tip I can leave with you is to do your research! Only use products which have demonstrable and guidance compliant independent test data, and most importantly, have been accepted by the regulator and/or ground remediation company responsible for the site remediation...assuming that they are suitably qualified to rubber stamp your design. If you submit your design acting as the waterproofing designer, the buck stops with you! It might be the best textbook spec and installation you have ever carried out, but if the products aren’t fit for purpose, you’ve got a problem!
As I mentioned at the beginning of this blog, there’s a lot more awareness today than there has ever been, but all good designers should apply the relevant standards and guidance from the start. Final dramatic comment - remember there is no statute of limitation on Corporate Manslaughter and Corporate Homicide Act 2007!