If you are building a basement for accommodation or recreation You will need to achieve a Grade 3 Habitable basement to comply with BS8102 the British Standard for earth retaining structures and you will want basement waterproofing guarantees.
The standard says you should involve a waterproofing expert from the start of the design process and seek there advice throughout, It is critical that the designer is the installer. If you engage an independent designer or manufacturer you will be opening yourself or your client to split responsibility.
You probably need a 10 year basement waterproofing guarantee to satisfy mortgage companies if you come to sell the property. The only meaningful guarantees are Products Insurance backed guarantees and GPI insurance to give some cover in the event that the installers cease trading.
These guarantees are not available through manufacturers or suppliers of waterproofing materials.
Most manufacturer’s do offer a guarantee of sorts but the terms and small print are always very clear ( if you look into the detail) They only guarantee the materials. In the event of a leak or a failure you the client will be arguing with the manufacturer and the installer about liability. This normally ends in an unsatisfactory outcome for the client. it can lead to years of dispute and in some cases financial ruin for clients.
The genuine basement waterproofing guarantee has to come from the installer and must cover design, supply of materials and installation.
Guarantees have to be covered by products insurance and PI insurance or they are of no value whatsoever.
The safest form of basement construction is always reinforced concrete with correct joint detailing. Attention to detailing and well installed concrete will ensure a reasonably water tight structure. This can then be guaranteed with a internal waterproofing system installed.
Other methods of construction will always require an external waterproofing system. External waterproofing is logistically difficult to achieve to necessary standards.
External membranes are affected by weather and so are often not achievable in the winter months.