Floor insulation of a warm winter garden on an unheated garage?

Hello, We are planning to renovate the old conservatory. It is built on an unheated garage. The base (24cm) was constructed with bricks, the floor is currently undamped floorboards. My idea would be: - Level the floor with leveling compound - Glue Styrodur or XPS inside to the base. - Approximately 20cm Styrodur/ XPS boards as insulation on the floor. - 22mm OSB boards floated on top On the finished floor, a floor heating system with 18mm installation height is to be installed (Fermacell-like boards with grooved channels for the pipes, then "filled in"). We have had these for years in the house on the old floorboards. Thanks for your tips and tricks

Hello Commocruiser,

your plan for the new winter garden sounds well thought out!
We also spent a long time thinking about the right floor structure for our winter garden in Munich, so here are a few tips from experience:

[*]Floor insulation: 20 cm Styrodur or XPS is a very good choice – especially indispensable for a winter garden above an unheated garage. Make sure to use pressure-resistant material (at least XPS 300) so that the floor remains stable.
[*]Base and edge insulation: Great idea to also cover the base with XPS. Additionally, an edge insulation strip is recommended to avoid sound and thermal bridges.
[*]Vapor barrier: Since your winter garden is on a garage, a vapor barrier under the insulation makes sense so that no moisture can rise.
[*]Pay attention to construction height: With insulation, OSB boards, and underfloor heating (e.g. Fermacell system), a considerable construction height adds up – therefore check the connection heights at doors and thresholds.
[*]Underfloor heating on OSB: Make sure that the construction boards are suitable for wooden substrates and are well fixed so that nothing creaks or works later on.

By the way, we planned a subsequent shading for our winter garden in Munich back then – otherwise it gets quite hot, especially in summer.

All in all, your concept is very well thought out! I wish you much success with your project – a cozy winter garden is really an enrichment for the whole home.

The construction sounds solid overall, but you should still consider a few things:

[*]XPS with sufficient compressive strength (at least 300 kPa) is mandatory, otherwise the underfloor heating will cause dents later on.
[*]Vapor barrier or vapor retarder under the insulation to prevent moisture from rising up from the garage – especially important with wood and OSB.
[*]20 cm XPS + underfloor heating + OSB = a lot of build-up height – check door connections and possibly also the railing height.
[*]And if the Fermacell boards are not explicitly approved for wooden substrates, clarify beforehand – there are variants for different substrates.

Otherwise: good plan, should work like that!