Balcony 1975 Renovation (Thermal Bridge)

Hello,

I have taken on a new project on our house. This time it is a balcony from 1975 where the concrete slab is integrated into the ceiling beam of the 1st floor. Since there is a completely newly renovated room including underfloor heating and interior as well as exterior insulation under the balcony, the balcony now represents a real thermal bridge. Since I cannot assess whether mold problems could occur in the long term, I would like to refurbish the balcony above (sealing + insulation). On the underside, I would repair the cracks and broken spots with some concrete. I would coat the existing tiles with liquid plastic and wrap the balcony with EPS insulation followed by new tiles. What do you think would be the sensible solution for this? I would also like to do all of this myself under professional guidance/suggestions.

Hi,

a simple doubling of the insulation on top (i.e. on the slab plus new tiles) only addresses the actual problem – the thermal bridge caused by the cantilevered concrete slab – partially, because the thermal connection to the house remains. In case of doubt, the risk of mold inside can be reduced, but never completely ruled out; the main issue remains the connection at the joint to the wall and the transition to the interior.

A truly sustainable solution would be a continuous installation of a special insulation element (e.g. Isokorb or comparable thermal break), which is much more complex. Alternatively, a professionally done external, continuous insulation (also on the underside of the balcony!) could improve the situation, but you have to plan the building physics precisely, otherwise moisture will be trapped.

Are you sure regarding the sealing and insulation layer sequence (especially with liquid plastic on old tiles) that the construction remains diffusion-open and no moisture is drawn inside? Otherwise, there will quickly be more trouble than before.

Have you already talked to a building physicist to clarify the dew point behavior and the connection to the house?

Good luck!

In a similar project in my circle of acquaintances, I quickly removed myself from the subject at the time. It was too critical for me due to the influences to be considered from God knows which building physics corner.

What I did notice back then, however, was that in the end the entire balcony was separated and a separate balcony in timber frame construction was attached to the house. It is said to have been the cheapest option in the end...

As part of our renovation, we had to answer the same question. In the end, we separated the balcony; everything else seemed botched to us. It is certainly possible to do it differently, but by now I am glad that part is gone.