Identifying Issues in a Basement Waterproofing Project

My top three issues are: 300mm secant piles seem inadequate to get meaningful overlap. If the piles do not overlap, especially with groundwater above basement level, the piled wall is likely to leak. Assuming 75mm concrete cover for in-ground structures your pile cage is only 150mm in diameter - how do you install concrete? How do you place shotcrete below top of basement slab (and why is shotcrete optional)? The water proof membrane between the piled wall/ basement seems to be inadequate...

Question is, did you fix it?

Follow Type C waterproofing detail?

Nice detail, but from a BS 8102:2022 perspective there are gaps. A single membrane against piles is risky for Grade 3 use – dowel penetrations, 75 mm shotcrete, and no maintainable drainage mean high water-ingress risk. BS 8102 stresses combined protection, typically a Type C drained system with pumps/alarms plus either a robust Type A or B structure. The wall–slab joint, uplift resistance, and continuity to DPC level also need attention. And critically, the land drain should be positioned outside the basement wall to manage groundwater properly.

Hacène Baleh, I know the OP is about waterproofing. The waterproofing issues already been highlighted by others, I'd raise the issue of condensation. The retaining wall will be keyed to the thermal mass of the earth, which if one is not careful with how the habitable space is conditioned, is likely to encounter condensation. Starting recommendations: (1) Insulate the retaining wall (2) create a wall cavity or service corridor with 24/7 dehum between retaining wall and internal wall (3) ensure the internal wall lining limits air ingress to that cavity (4) regulate permeability of the line marked 'Plasterboard', no higher than Class 3 VP classification to AS4200.1.

Rather than over complicate things I’ll add my two main points only. Penetrating dowels for obvious reasons 300mm secant piles only allow for a small overlap.

Poor detail. Very briefly....Secant piles can be a Type B form of waterproofing if designed correctly by engineer. Would prob need to be bigger dia here for male and female to provide continuity. Slab is tied into piles to resist uplift, but theres a massive hole which some commenters are assuming is either a land drain or a type C system. Both wrong and ridiculous. Structure should be capable of resisting heads of water pressure and should be water tight to tightness classes in BSEN1992 part 3 or old BS8007. Inside of a watertight structure a CSSW qualified designer may use further Type A and min 250mm RC liner wall cast in situ and may use an internal Type C system draining any seepage to sumps formed within base slab- no holes in slab! An SIR needs to be provided ( for water, radon, ground gas/contamination and flooding and a specialist should be involved in design AND installation. Someone who thoroughy understands all sections of BS8102:2022. This will get you to grade 2. An M&E consultant will then take it to grade 3 with appropriate air systems. Get in touch with me or ASF if you need more in depth solutuons.

“The least initial deviation from the truth is multiplied later a thousandfold.” – Aristotle In structural waterproofing, this rings painfully true. A bad design detail — even if made with good intentions — is not a small mistake. It is the seed of failure, and its consequences multiply throughout the project. What we see far too often in our industry is not just a missed line on a drawing, but a fundamental misunderstanding of BS 8102:2022. In fact, more than 50% of the proposed waterproofing designs we review are either completely opposite to the intent of BS 8102:2022 or fail to even consider it. Waterproofing is not a matter of patching isolated walls or adding products as an afterthought. It is about designing a holistic, integrated system that meets the principle of the standard from the start. Anything less is simply a bad design — and in this field, bad design always costs far more to correct than to get right the first time.

For me, if a waterproofing membrane is supposed to be used, it should have been installed on the positive side (outside wall). If in case this is not possible (constraints like existing building at the perimeter etc.) then the proper waterproofing material to be used on the negative side of the wall should be cementitious crystalline waterproofing. This is so it can resist water penetrating the wall. As addition for the slab, we can recommend using HDPE and bitumen joint fillers prior to pouring of cement floor.