Balcony drainage detail
Hi everyone,
I’m looking for some professional advice on a detail involving a steel balustrade and drainage at a balcony with a projecting slab.
The main issue is that I would like to avoid using a conventional floor drain, mainly because the balcony has a relatively shallow depth. I’ve attached a schematic section showing the proposed assembly.
The balustrade needs to penetrate the final floor finish (stone or porcelain tiles), which is designed to project beyond the edge of the concrete slab and form a drip edge on the outside.
My initial idea is to use intermittent steel L-brackets anchored into the reinforced-concrete slab. These brackets would serve two purposes:
provide support for the floor build-up at the balcony edge, and
provide a vertical steel element to which the vertical balustrade profiles could be welded.
I’m intentionally using the vertical part of the L-profile so that I can achieve a longer weld between the balustrade and the support, while keeping the balustrade itself as visually minimal as possible and using the fewest steel profiles possible.
The concrete slab would be thermally insulated on all sides, which I believe is relatively straightforward.
The part I’m struggling with is the drainage and waterproofing of the balcony surface, particularly how to deal with the steel penetrations.
My current idea is to use a liquid-applied waterproofing membrane, such as Mapei Mapelastic or a similar system, applied over a cement screed and underneath the final stone/porcelain finish. This seems like a good solution because it should allow the waterproofing to be properly detailed around the points where the steel penetrates the floor.
There are quite a few similar examples online, for instance in projects by David Chipperfield, so I assume this type of detail is technically feasible. One thing I’ve noticed is that in many of those examples the balustrade is set slightly back from the edge of the slab, which probably makes the waterproofing detail somewhat easier.
Another complication is the dimensioning of the floor finish. Ideally, the width of each stone/tile would correspond to the centre-to-centre spacing of the balustrade profiles, meaning that the pieces would need to be notched around the vertical steel penetrations.
Has anyone here actually dealt with a detail like this, or would you recommend a completely different approach?
I’d be particularly interested in advice on waterproofing, drainage, and how to properly detail the penetrations through the finished floor, rather than just the structural aspect of the balustrade.
Thanks in advance!