ᐅ Insulating the Balcony Slab from Below in a Conservatory

Created on: 8 Apr 2026 21:11
D
Denner
D
Denner
8 Apr 2026 21:11
Hello house building community, I live in a semi-detached house (built in 1975), where a wooden conservatory was added to the living area in the 1990s. The balcony slab is therefore part of the ceiling of the conservatory. Cable ducts run there as well, leading to the shading system. Pictures attached.

For aesthetic reasons, I would like to cover the underside of the balcony with wooden paneling. This raises the question of whether I should install insulation material underneath at the same time, so that in winter the cold does not pass through the slab from the outside of the balcony into the conservatory. If the sun does not warm the conservatory enough in winter, it is rarely used and heated to about 12°C (54°F).

I have the following questions regarding insulation:

1) What is the best way to build this insulation to reduce cold entering the living space while also preventing mold growth underneath? I have about 13 cm (5 inches) of installation height.

2) What should I do about the gap between the conservatory and the concrete slab? The end of the gap closes again at the wood of the conservatory. A short section was previously filled with expanding foam.

I would be very grateful for expert advice.