Thermowood for Balconies: Cladding Walls, Ceiling and Floor

The balcony of an apartment is usually the smallest and least used part of the home, but with the right cladding it can become a pleasant corner. Thermowood is a common choice because it is more stable than ordinary timber when moisture and temperature change. This article covers what to watch for on balcony walls, ceilings and floors.

Why thermowood suits a balcony

Thermowood is timber heat-treated at high temperature without chemicals; the process lowers the equilibrium moisture content of the wood and improves dimensional stability. For a balcony that faces sun, wind-blown rain and day-night temperature swings, that stability is the main advantage. The light weight of the boards is also a plus in apartment buildings, where every kilogram on the structure counts.

On a balcony, ventilation behind the timber matters more than the species.

Cladding the balcony wall

Thermowood boards should not be glued straight onto a wall. A substructure of battens (timber or corrosion-resistant metal) is fixed to the wall first and the boards sit on it, so that air can move behind the wood. If the wall is damp, the cause must be fixed before installation, or the timber will suffer too. In our article on the ventilated timber facade we explain the ventilation gap in more detail.

Cladding the balcony ceiling

A balcony ceiling is often exposed to damp from above or leaks from the floor overhead. Before installation the ceiling must be dry and waterproofed. Thermowood boards are fixed with hidden clips or stainless screws so that they can move freely with seasonal expansion and shrinkage. When cutting, always treat the cut ends with oil made for thermowood, since a cut surface takes up moisture faster.

The balcony floor: slope and drainage

A balcony floor should have a slight fall toward the drain. Thermowood boards are laid on a raised substructure so that water does not collect under the timber and has a way out. If the floor is a covered balcony rather than an open terrace, the gap between boards can be slightly smaller, but boards are never laid without gaps. More on floors is in our article on thermowood terrace flooring.

Sunlight and thermowood colour

Ultraviolet light gradually turns the brown of thermowood into a silvery grey. This is natural and does not harm the structure of the wood. If you want to keep the original brown, apply a UV-protective oil or coating once or twice a year. On south-facing balconies the change appears faster. The upkeep method is explained in our thermowood oiling guide.

Check these before you order

• Make sure the building management allows a change to the balcony facade.
• Have an engineer check the load capacity of the balcony and ceiling.
• Ask the supplier about the species, the heat-treatment grade, and the screws and clips.
• Decide the drain plan and the water outlet before installation.

With the right substructure, enough ventilation and yearly upkeep, a thermowood balcony can stay attractive and durable for years without adding extra load to the structure.

Sources

• International ThermoWood Association — ThermoWood Handbook