Combination waterproofing is a construction strategy that does exactly what it says on the tin: it combines a number of waterproofing systems to more effectively protect a structure from water ingress and subsequent damage. It’s frequently seen in sub-level constructions, such as basements, tunnels, lift pits, and retaining walls.
It’s also a good method of ensuring whatever needs waterproofing adheres to BS 8102:2022 guidelines. BS 8102:2022 is the UK’s guidelines that stipulates how best to protect sub-level spaces from groundwater and water ingress. It offers guidance on how best to carry out waterproofing for a range of designs and is considered an industry benchmark. It covers evaluation, risk assessment, and the best designs for cases. You can read more about it here.
Types of Waterproofing
There are three types of standardised waterproofing:
- Type A: Also known as Tanking, this method normally requires the application of a waterproof slurry to a below-ground structure. It can be installed on either the interior or exterior of the structure, or placed between the walls and flooring of the space. The waterproof material used is often either a multi-coat render or a bonded sheet membrane that can be directly applied to the walls. Both materials essentially act as a hard barrier to prevent water ingress.
- Type B: This solution offers water resistance at a structural level. It is usually reinforced concrete, with waterproofing elements and careful joint detailing which helps it to resist water ingress.
- Type C: Type C waterproofing consists of a cavity drain membrane that collects any water that enters and channels it to drains, or more commonly a sump and pump system. Type C differs from the above as, rather than just block water entirely, works on the assumption that some water will always manage to penetrate through external walls. Studded plastic membranes are affixed to the inside of walls and floors, with the void of space between the membrane and the wall allowing water to be safely captured and contained, before flowing down to the bottom of the system, into drainage channels which diverts the water away into the sump pump system.
What is Combination Waterproofing?
Combination waterproofing essentially combines two or more of the above-mentioned solutions. Often, it is Type C with either A or B added in as well to create a truly water-protected environment, particularly suitable for basements that are being turned into places for living or storage. Combination waterproofing is considered highly effective as it prevents water as much as possible, and in the event it does manage to get past the first barrier it ends up being directed and managed before it can start causing problems to your property.
When is Combination Waterproofing Used?
A dual combination of waterproofing is often used in these particular instances:
- The chances of a property being susceptible to leakages is higher than normal. Scenarios include properties being built in potential flood zones, properties built next to bodies of water, or instances where there is significant pressure from groundwater.
- The consequences from water ingress can be particularly damaging to a structure or cannot be tolerated. A good example for the former would be a basement that is being converted to be habitable. As for the latter, restaurants using a below ground structure for food storage would be applicable.
- Vapour checks are required.
- Basements and below-ground structures require two forms of waterproofing to be considered compliant to BS8102:2022 standards, so in cases where only one form of waterproofing is present, another form will need to be installed to make the basement properly waterproof.
- Tunnels and underground infrastructures where water can enter through joints, cracks, and surrounding soil pressure.
- Buildings with complex shapes or many joints, which can create numerous entry points for water and need different waterproofing solutions.
- Roofs or terraces with difficult conditions, where a membrane may be combined with coatings or drainage layers.
- Structures exposed to severe weather where extra protection is needed against rain, moisture, and temperature changes.
What are the Advantages of Combination Waterproofing?
There are a number of benefits to using a dual method of waterproofing, most of which are usually fairly apparent:
- Enhanced protection against water; two is always better than one.
- Enhanced durability.
- Enhanced protection against adverse weather conditions.
- Reliability; if one system slowly becomes weaker, the second will still be there to protect against ingress.
Considerations
BS 8102:2022 guidelines stipulate that the area needs to be assessed by a qualified surveyor, who will also manage the construction of it. Timberwise can take full responsibility for the design and liability for the basement waterproofing design in your building project and our systems also meet the guidelines set out in NHBC chapter 5.4 and Local Authority Building Control (LABC) guidelines.
A combination of two forms of waterproofing is adequate when designing a habitable space requiring a completely dry internal environment, defined as ‘Grade 3’ within BS 8102:2009. Whichever combination of waterproofing is chosen to achieve the Grade 3 environment, in most cases the safest combination will include a ‘Type C’ internal cavity drain membrane system as one of the forms of waterproofing as Type C systems are quick and easy to install in any structure, regardless of its shape, size, or age.
Looking For a Waterproofing Solution?
At Timberwise, we have over 50 years of specialist experience in high quality waterproofing solutions for every scenario. If you have problems with water ingress to your sub-level spaces, contact us today by calling on 0800 288 8660 or request a free survey online.
A survey through Timberwise will be able to identify the extent of the problem and determine the right waterproofing solution for you and your property.
