Insulation and sealing of balcony on bay window

Hello everyone,

we have planned a balcony on a bay window. Can someone tell me how this is usually sealed and insulated?
On the upper floor, we have planned a floor construction of 15 cm. How high will the construction on the balcony be? Is 15 cm or less sufficient?

Thank you very much!

Unfortunately, there are too many unknown factors for a conclusive answer, but 15 cm from the top edge of the concrete slab including thermal insulation is generally too little for a balcony construction.

Thank you very much for the reply. Isn’t it the normal case that one has a floor construction of 15 cm and then has to seal and insulate the balcony on the bay window at the height? Or how else does one construct a balcony on a bay window?

I can't tell you how it is prescribed or generally required nowadays. When we built our house in 1990, we had a 15sqm roof terrace of the upper floor apartment directly above the dining room of the ground floor apartment, which we had done by a local service provider with an excellent reputation after the construction was completed. He first welded tar paper or similar onto the raw floor, attached a wooden frame at the edge, and then applied a leveling fill ("perlite" or similar), on top of that a tray made of so-called Elefantenhaus, which he pulled up at the sides and fixed with a corresponding aluminum rail. The roof terrace was then covered with 4 cm panels on pedestals. We never had any problems with the roof terrace, neither in the upper floor itself nor in the apartment below, neither with moisture nor with cold, and to my recollection the fill was at most 10 cm high, rather a few centimeters less. But as I said, possibly different guidelines are applied nowadays, so I can only tell you how we did it and that there were no problems.

Is it a new building? The insulation on the bay window ceiling largely determines the total construction height, depending on the requirements of the Energy Saving Ordinance. I would always recommend creating a slope. There is finished insulation available for purchase that already has a slope. The waterproofing membranes add hardly any height; usually, a waterproofing membrane is applied directly on the concrete, then the slope insulation (~8-16cm high), then the water-carrying balcony waterproofing (various options), then e.g. pedestal supports (at least 1cm) and a tiled covering (at least 2cm).

The general rules foresee a height difference of another 15cm from the top edge of the tiled covering to the door threshold. If you decide on a nice barrier-free design, a drainage channel should be placed directly at the window so that heavy rain cannot penetrate at the lower door frame, nor snow.

In new buildings, the simple solution is therefore regularly e.g. a step inside, or doubled-up door frames at the bottom. Both are naturally not particularly elegant but more fault-tolerant in execution and thus the developer’s favorite. If level exits are desired with good insulation, the bay window ceiling can be constructed with a height offset on the upper side during concreting. This just needs to be correctly planned in advance regarding the connection heights.

There is also especially flat vacuum insulation with significantly better insulation values – but correspondingly expensive and with other disadvantages.

I am currently facing a similar problem. However, everything is already in place.

I have about 13 cm from the door threshold to the raw concrete. On top of that should be as thick insulation as possible and, of course, the terrace flooring.

At the moment, I am planning to lay a 10 cm XPS or PUR board with a slope. The terrace does not get much moisture, but during a heavy thunderstorm it can get wet. So the XPS boards definitely need to be sealed.

As for the further structure, I am still unsure. Will tiles hold up in the long run? Pedestal supports would also be an alternative.

What worries me is the construction of the railing. The terrace was enclosed with Styrofoam retaining blocks. Therefore, the current terrace structure probably needs to be sheet metal clad.

How would you design the structure?