We are basement conversion & waterproofing specialists covering Leeds, Harrogate, Wakefield & surrounding areas. We have been waterproofing structures for 27 years, so its fair to say we know a thing or 2 about this subject.
We offer services to trade, commercial and domestic clients so whether you require waterproofing only, refurbishment or a basement conversion we are able to help!
Below you will find information on the basic principles of waterproofing to give you an understanding of what you will need to achieve if you are looking to maintain or create a dry basement space.
Getting it right from the start
Many claim to be experts on basement waterproofing and will tell you that they know what they are doing but in reality, they lack understanding of the subject, have never had any form of formal training and do not hold any certification. So really all you have is their word that they know what they’re doing. But is this really good enough when you are about to invest in creating valuable new space in a high-risk area?
Below we have created a list of qualities that we feel a true specialist should have, which demonstrate a commitment to giving you the level of service and confidence you deserve.
Qualified Surveyors & Designers
There is only one industry recognised qualification for a structural waterproofing surveyor – CSSW (Certified Surveyor in Structural Waterproofing).
This qualification is only awarded once a surveyor has demonstrated their understanding of the subject by sitting and passing a written examination, an oral examination and separate examination covering health & safety, and legal aspects of their role as a surveyor.
The CSSW qualification is widely called for by many within and linked to the construction industry, including specifiers and major warranty providers/insurers, such as the UK’s leading provider NHBC.
Knowledge of BS8102
BS8102 is the British Standard for waterproofing below ground structures. Last revised in 2009, the standard titled ‘Code of practice for protection of below ground structures against water from the ground’ contains the key design principles a waterproofing designer must consider when designing a successful waterproofing system. This standard was compiled by industry experts and replaced the former standard BS8102:1990.
If a specialist does not mention this standard to you or does not know what it is then avoid them at all costs!
A Qualified Workforce
Waterproofing systems need to be installed by skilled technicians. The slightest error can result is a catastrophic failure. For this reason, it is important that those responsible for installing waterproofing systems have been able to demonstrate their knowledge and understanding of the subject.
An NVQ in Sub-structure Work Occupations (Construction) – Structural Waterproofing as well as The Property Care Association Qualified Technician certificate – PCAQT (Structural Waterproofing) should be considered as the industry standard.
Excellent Product Knowledge
Waterproofing products differ from one another. Although some materials may share performance principals there can often be many varieties of a material, even from the same manufacturer. Each can differ substantially in the way it is applied and forms. For this reason, it is important to be familiar with different manufacturers product ranges and installation guidelines.
We only buy our specialist materials direct from the manufacturer or their approved distributor. We have a good relationship with these suppliers and technical support is always available from design stage through to after sales. This ensures that we have the latest information on products ranges, training directly from the manufacturer, piece of mind that our design incorporates the best product for the job and that the materials are from a fresh source where they have been stored correctly.
There is no such thing as a one fit solution and you will NEVER find a full product range in any builders merchants yard not to mention technical advice or training.
Guarantees that ARE worth the paper they are written on
A guarantee is a promise from the guarantor to the beneficiary. The promise is usually a set of rules or statement bound by terms and conditions that if adhered to mean that the guarantor will keep their promise.
A guarantee is worthless if the guarantor is unable to honour it, for example, if the company that has issued the guarantee is no longer trading.
Many guarantees are not worth the paper they are written on. A consumer may think they are getting a long-term promise from the installer but in reality, they are not as the contractor will cease trading at the first sign of trouble leaving the consumer with no protection. In some instances, the guarantee may not even cover workmanship and simply relates to a material that has been used. These guarantees are particularly worthless as the material manufacturer will simply provide a replacement material if that, that is installed is found to be at fault. This is almost never the case as poor workmanship is usually to blame.
When choosing a contractor it is advisable to check one or two things. How long have they been trading? Do they have a good trading history? What are the terms of their guarantee? Don’t just take their word for it. It is simple to carry out background checks on a company for free online.
The sign of a reliable company is one that has been able to demonstrate reliability and integrity. This will result in backing by other professional organisations such as guarantee insurers offering insurance backed guarantees.
Insurance backed guarantees (IBG’s) comes in many forms but a bona fide insurance backed guarantee is one that is insured for the full term from the point at which it is paid for – such as one offered by The Guarantee Protection Insurance Company Limited.
BEWARE – Some guarantees that claim to be insurance backed are not truly insurance backed. They rely on a third party to keep up with insurance payments on an annual basis. If this third party cannot or does not pay the insurance then that is the end of the guarantee. Avoid these!
You often see adverts where a tradesperson states they are fully insured. But what is being fully insured?
To us, it includes not only statutory insurances such as employers and public liability, but also trade specific insurances such as professional indemnity (PI), product liability and product guarantee insurance with insured sums being realistic.
It also means that we have declared the types of work that we offer to undertake. Waterproofing is considered a high-risk trade and as such insurance relating to it is usually higher than other trades.
Remember, if a waterproofing designer or installer is not correctly insured, they will be unable to cover costs if things go wrong.
We are proud to be able to tick all of the above boxes and we know that only a relatively small number of other specialists within the Yorkshire region can too!
Survey & Inspection
The current nationally recognised basement waterproofing surveying qualification is C.S.S.W. – Certified Surveyor in Structural Waterproofing. All projects that include structural waterproofing should be overseen by someone with that level of qualification.
There is only one satisfactory way of determining if a basement/cellar area is suitable for conversion and that is by consulting qualified experts. The expert should be invited to view the area so that a full investigation of the potential risks to the area can be made. The person who is going to be the end-user, client, bill payer or who has a direct interest in the conversion MUST be closely consulted. This is so that the exact requirements of the client are established, and especially so that the risks of flooding can be fully discussed and understood. It is no good taking a decision to leave out a sump and pump system to save money, and then be standing in inches of water years on. It is even more unacceptable to be in the same position and not to have known that it might happen. This problem is the most frequent cause of litigation between the client and the installer – and this is to be expected. After all, the client will have wanted a dry and usable basement.
What is Basement Waterproofing & Why Do I Need It?
Put simply, basement waterproofing is the process of protecting basement structures from dampness and water in the ground.
Basements are below ground and as such, they are susceptible to differing forms of dampness and water such as:-
There is a British Standard to help with the design of waterproofing systems for basements : BS8102: 2009 Code of practice for protection of structures against water from the ground. All good companies, with qualified surveyors (C.S.S.W. – Certified Surveyor in Structural Water-proofing), will refer to this standard early on in discussions with you. Those that don’t should be avoided!
Any specification you are offered should state clearly if BS8102 has been considered. Those that do, require the surveyor to design a waterproofing system that can be expected to withstand entry of groundwater into your basement. Note: this does not normally include water that arises from leaking drains – although the system might well deal with that too.
Those systems that do not consider the requirements of BS8102 are unlikely to come with any guarantee against water entry from the ground or the guarantee may be questionable. In most cases, these conversions have excluded the drainage part of the system or the drainage system may be substandard, often to save cost.
To avoid confusion, the best way to refer to these treatments is to refer to them as “waterproofing”. This can then be sub-divided into tanking and cavity drainage membrane (CDM) systems.
Understanding the principles involved in waterproofing a structure allows the risk of failure of the system applied to be reduced to an acceptable level. Furthermore, with forethought, systems can be used where, should problems occur, remedial / repair work can be carried out without excessive disruption.
Basement/cellar waterproofing is the application of a covering to masonry usually, but not necessarily, below ground, to prevent or control penetrating dampness or water ingress. The masonry can be treated from outside or inside, but most waterproofing to existing buildings is carried out from inside, as access to the outside is not possible or practical. Waterproofing and the types of systems in use is a complex subject. We cover only the basic details here. Each project will have its own conditions and requirements and therefore require specific expert advice.
The type of waterproofing chosen depends on the conditions which it is trying to deal with. This is the control of water vapour, or a little liquid water or considerable amounts of water. The use to which the area will be put is also important. Both tanking and CDM systems can deal with all of the above, but the performance of each system has different results and different effects on the structure to which it is being applied. This is such an important feature that in some cases only one of the system types will be suitable. Choice of the wrong system could result in structural failure of the building components. This is another reason why expert advice is needed.
Grades of Waterproofing Protection
British Standard BS8102 : 2009 – Code of Practise for Protection of Structures Against Water from the Ground defines performance levels for the dryness of buildings in three grades as follows:-
|Grade||Basement Usage||Performance Level|
|1||Car parking, plant rooms (excluding electrical equipment), workshops||Some water seepage and damp areas tolerable dependent on the intended use. Local drainage might be necessary to deal with seepage.|
|2||Plant rooms and workshops requiring a drier environment (than grade 1), storage areas||No water penetration acceptable. Damp areas tolerable; ventilation might be required.|
|3||Ventilated residential and commercial areas, including offices, restaurants, leisure centres etc.||
No water penetration acceptable.
Ventilation, dehumidification or air conditioning necessary, appropriate to the intended use.
In most cases, a Grade 3 (Dry Environment) level of protection is required for habitable use or for storage of anything that could be damaged by moisture.
Types of Waterproofing
British Standard BS8102 : 2009 – Code of Practise for Protection of Structures Against Water from the Ground defines different types of waterproofing system. There are 3 recognised waterproofing types:-
|B||Structurally Integral Protection|
It is generally considered best practice to install dual systems which comprise of 2 different types of waterproofing as this provides a failsafe in case the primary waterproofing barrier fails. When converting an existing basement this is not usually practical.
Tanking (Type A - Barrier Protection)
Type A Tanking can consist of:-
- Cement based coatings and multi-coat render systems
- Liquid applied bituminous & synthetic rubber coatings
- Externally acting liquid injected resins, installed from inside the structure, acting from the outside
- Plastic, bituminous and rubber membranes
Method 1 requires a high level of original surface preparation as these coatings are designed to stick or key to the walls being tanked. If they fail to key then water under hydrostatic pressure (penetrating dampness below ground) can force the material to debond from the original surface and break the tanked surface. Some variants are particularly well suited for new concrete and as such work very well on new build structures.
Method 2 is a particularly useful as liquid applied membranes are often more flexible than other forms. Large areas can also be covered in a time efficient manner using spray application. These systems are usually suited to external use as waterproofing barriers but may also be used internally as vapour barriers.
Method 3 is a niche product that is usually selected for tanking failure repairs of say movement or casting joints.
Method 4 is a common method of tanking for new build properties, often in conjunction with other forms of waterproofing.
Tanking (Type B - Structurally Integral Protection)
Type B tanking is usually waterproof concrete. This is concrete strictly manufactured using specific grades of sand correctly mixed with the correct ratio of cement. Often there are admixes introduced to the concrete to aid its waterproofing properties.
Type B tanking systems will be formed by casting the concrete in stages. The construction joints will incorporate a hydrophilic water bar. This is a type of seal that will swell in contact with water thus sealing the joint tightly so that water cannot enter.
Type B waterproof concrete systems are almost certainly exclusive to new build.
Cavity Drainage Systems (Type C - Drained Protection)
A cavity drainage system manages water ingress using membranes and drainage.
The membranes used are specifically designed for this purpose. They are formed using extruded high-density polyethene, sometimes coated with thermically bonded polypropylene mesh to aid with the adhesion of finishes. They have a profile similar to an egg box or the sole of a football boot and are often referred to as studded or dimpled sheet membranes. The membrane is loosely mechanically fixed to walls using sealed nylon plugs.
The purpose of the membrane is to form a cavity between the membrane and wall/floor. This cavity allows groundwater to freely run under the influence of gravity towards the base of the wall into a planned drainage system. The air gap also allows some degree of breathability behind the membrane whilst working as a vapour barrier, limiting moisture vapour from reaching the room.
There are 2 methods of providing drainage for cavity drainage systems.
Method 1 – Perimeter Drainage
This method involves a prefabricated void forming channel to be placed around the perimeter of the basement, usually at the floor wall junction. In larger basements or basements with a complex circumference, additional channelling may be installed to link runs of perimeter drain.
The channel will lead to a removal point such as an external drain or sump chamber.
Method 2 – Modular Drainage
This method involves the placement of a 110mm drainage network into the floor slab with an opening created in the floor at centres of around 1 every 12 square metres. This method allows water to run below the floor membrane where the drainage holes act as a plug hole.
The drainage network will lead to a removal point such as an external drain or sump chamber.
With either system access to inspect and service the drainage channels must be allowed for in the design.
Sump & Pump Systems
When water cannot be taken away from a basement safely and reliably using gravity drainage then a pump station will be required.
This will normally comprise of a prefabricated plastic sum chamber sunk into the floor of the basement. Within the sump chamber, a pump arrangement is then installed. This is an automatically float activated system with a high water alarm.
Again, component failure should always be allowed for in the design. It has now become the norm and considered best practice for pump systems to comprise of 2 pumps (a primary and backup) as well as a battery back up (uninterrupted power supply – UPS) system. This means that if the first pump fails then the second pump will activate either by mains power or in the event of a power failure then the UPS.
Pump systems technology has rapidly developed in recent years. It is now easily possible to monitor pump system remotely and as well as receiving notifications in case a major component fails.
As a pump system is a mechanical system it should be serviced to ensure its functional service life is maintained.
Typical Cavity Drain System Components
The following videos show a typical installation of a cavity drainage system using components from our supply partner – Delta Membrane Systems
With internal waterproofing systems, surfaces will require finishing after waterproofing.
Wall surfaces are usually lined with either treated battens, metal stud and other framing systems on to which insulation and plasterboard can be fixed. In some circumstances, the batten or framing can be omitted and plasterboards fixed using adhesive methods to membranes coated with a polypropylene mesh.
Other finishes are possible depending on the final use of the area. These include membrane only, plywood, timber panelling and other wall boarding materials. The finish chosen will be governed by the use to which the converted area is put.
Flooring can be finished using a concrete screed or a floating floor. Whichever method is used insulation needs to be considered.
With any finishes that are installed, damage should be avoided to the membranes or tanking as damaging these can lead to a system failure.
No waterproofing system eliminates the occurrence of humidity within a basement, so consideration needs to be given to controlling/reducing relative humidity using heating, ventilation, air conditioning, dehumidification or some other method.
As humidity can vary, particularly in occupied basements, it is not always possible to identify exactly what will suffice at a design stage. For this reason, it is always worth taking a ‘belt and braces’ approach with a design and over-engineering requirements. Even if these are not used, they could be put into service in the future.
We have found the requirements of our clients to be very varied and each basement must be treated on its own merits given the individual circumstances found.
Prior to any inspection, we recommend the following are considered:-
What do you plan using the area for?
What is your budget?
Do you require more head height? If so, will foundations be exposed and will underpinning be required?
What internal joinery is required? (doors, architraves, skirting boards etc..)
Are ceilings required? (hiding pipe and wire runs)
Do you require new windows and external doors? (natural light, ventilation, means of escape)
Do you require plumbing or drainage system alterations? (extra radiators, bathroom or kitchen supplies and drainage)
Do you require electrical system alterations? (extra plug sockets and lighting)
What sound and thermal insulation do you need?
What level of heating, ventilation and condensation control do you need?
Are there planning, building control or environmental health regulation requirements?
Do you need fire escapes and alarms, and security alarms?
Building Regulations and BS8102 require designers of waterproofing systems to consider contamination of sites by ground gases. Radon and other ground gases, such as methane, are now more recognised as contributors to health and safety in buildings – and especially basements. Those designing basement systems must consider the possibility of ground gases in any design, and this is now a requirement of Building Regulations and Codes of Practice.
A desk-based on-line search can be done to locate the risk of radon at your property. We automatically offer this for you as part of our design service for basements. The outcome of any radon search will categorise the ground around the property as requiring no action, or a basic radon barrier system, or a full positive ventilation radon control system. The latter two require the introduction of additional materials and installation techniques to create a system to provide the level of protection designated. The positive ventilation system requires additional components to force air to move behind membranes to extract ground gases, such as radon. These systems have additional costs over and above standard basement waterproofing, but the costs can be controlled by designing in ground gas control as an integral part of the waterproofing system. The UK maps identifying areas of high radon contamination can be seen at UKRadon.org website.
We believe that if a job needs doing, it needs doing right, first time. To achieve this it is important that the products we use meet and advance beyond our high expectations. Therefore, we only buy from industry leading manufacturers. But it doesn’t end there, our relationship with our suppliers is great! We talk to each other, we support each others and we understand each others needs. This allows us to provide our customers with the best products and advice from the product designers, manufacturers and experts direct to your property.