Syntegra Consulting took part on the 28th of November at a webinar organised by Building and RIW on “The essential guide to structural waterproofing”. The webinar explored the BS8102 specification and design principles for a successful waterproofing strategy, looked at different system choices and their application with case studies including Berkeley Home’s Royal Arsenal Riverside development. The webinar brought together a panel of expert speakers to debate these issues as Mark Anstee, Technical Adviser at RIW Ltd, Bob Treadwell, Technical Director at Waterman Transport & Development Ltd and Nick Simms, Project Manager at Byrne Brothers.
A successful waterproofing strategy is essential in today’s fast-track construction environment. Deep basements, complex foundations, different substrate materials and changes in levels can test the continuity of the waterproofing strategy. Guidance and design principles are available from Building Regulations, Waterproofing specialists or the code of practice BS8102 which states “the protection of structures against water from the ground”. Waterproofing systems and waterproofing specialists should be involved at an early stage of a development within the design team to provide the best option. Structural, weatherproofing and waterproofing design should be considered all together as they interact and a line of communication should be established and maintain between all designers, waterproofing specialists and contractors. This is a result as modifications on the design of the development decided by others could impact on the waterproofing strategy.
To develop a robust design to protect the structure from the water, the design team and client must agree on the intended use of structure and the acceptable level of water tightness. The design team should decide on the form and design of the structure and undertake a risk assessment on the external environmental conditions. There are four design principles to take into consideration as the basement usage site information, form of structure and waterproofing. The first criterion is particularly important as it sets the performance level of the basement depending of the usage as shown on the table below.
The second principle is to gather site information (BS5930) about the geology, topography of the site, soil type, pollution (gases) and the water table which is divided in three categories, low, variable and high.
Assessing the water table:
- permanently low
- permanently high
Drainage system may be also used to lower the water table:
The third and final principles are based on the form of the structure and the waterproofing (A, B and C).
External tanking: The membrane is supported on the wall and the structure remains dry. It also protects the structure from harmful chemicals/gases, however, this system requires land drainage and it is difficult to inspect due to the membrane located on the external wall basement. The type A external tanking can be use for basement grades 1, 2 and 3.
Internal tanking: With this system external excavation is not required as the waterproofing system is located inside the basement and controlled environment apply to membrane. However, it requires an internal loading skin, usually screed, which also reduces the internal space. Land drainage is needed and can be use for basement grades 1, 2 and 3.
Type B – Internal Protection
The type B has some limitations and to avoid cracking, poorly compacted and honeycombed concrete it requires a quality workmanship, a correct concrete placement, thorough joint preparation, curing.
Type C – Drained Protection
It is suitable for grades 2 and 3 with a high water table and requires a cavity drain with pump to collect and remove the water in order to minimises water ingress.
To provide a good waterproofing system it might be considered to combine forms of construction in order to get the best results.
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