Hygrothermal comfort is the state of well-being achieved when air temperature, surface temperature, relative humidity and air movement remain balanced indoors. It does not depend on a single declared technical value, but on the overall behaviour of the building envelope over time.
What is meant by hygrothermal comfort?
An insulation material cannot be assessed solely on the basis of its declared thermal conductivity. Indoor comfort also depends on the envelope’s ability to attenuate temperature variations and manage the moisture generated indoors every day. In hemp-lime biocomposites, such as TecnoCanapa systems, the material’s porosity influences this behaviour together with the continuous processes of water-vapour absorption and release, which can contribute to stabilising the indoor microclimate.
Parameters that influence indoor comfort
To assess a hemp-lime envelope correctly, several parameters must be considered together rather than in isolation:
- thermal conductivity;
- heat capacity and mass;
- thermal attenuation and phase shift;
- water-vapour permeability;
- hygroscopic capacity;
- wall surface temperature;
- continuity of the layer build-up;
- thermal bridges and construction details.
Walls with a similar U-value can behave differently if their heat capacity, mass, material structure and moisture management differ. A project assessment must therefore consider the entire construction system, not only the nominal value of an individual component.
The role of humidity: hygroscopicity and breathability
Indoors, breathing, cooking, use of bathrooms and drying fabrics produce water vapour every day. This vapour moves according to pressure differences and interacts with surfaces and materials. Porous materials such as hemp and lime temporarily absorb part of this vapour and release it when conditions change. This behaviour, known as hygroscopicity, does not replace air exchange, but it can reduce the speed and intensity of humidity peaks.
- Hygroscopicity: the ability to absorb and release vapour in response to changes in environmental conditions.
- Vapour diffusion: the passage of vapour through the material’s porous matrix.
- Breathability: the ease with which vapour passes through a layer or layer build-up.
Hemp and lime have a structure that favours vapour diffusion. To preserve this characteristic, plasters, skim coats and paints must also be selected consistently: a finish that is too impermeable restricts the behaviour of the entire wall build-up.
Condensation and critical points to avoid at the design stage
Condensation forms more readily on cold surfaces, at thermal bridges, in poorly ventilated cavities and in shaded areas. Design must therefore control continuity of insulation, surface temperatures, vapour diffusion and indoor ventilation. No material on its own can eliminate problems caused by design errors or incorrect use conditions. This is why TecnoCanapa supports designers and contractors in assessing the most critical construction details.
Dynamic performance: beyond steady-state U-values
Steady-state thermal transmittance describes heat flow under simplified conditions, but real buildings experience daily and seasonal variations in temperature, humidity, solar radiation and ventilation. It is therefore advisable to supplement steady-state values with dynamic parameters and verification under actual operating conditions, in order to understand how the system behaves throughout the year rather than only on paper.
TecnoCanapa solutions for hygrothermal comfort
TecnoCanapa Bioedilizia® offers different solutions for building and upgrading with the hygrothermal comfort of the complete envelope in mind. Biomattone® infill walls complete load-bearing structures with lightweight, vapour-permeable perimeter walls, while Canafiber Cappotto provides external insulation for existing façades. For roofs and attics, the reference solution is described in the guide to hemp-lime roof and attic insulation. Each project must in any case be assessed with the TecnoCanapa technical department according to its structure, climate and required performance.
Frequently asked questions about hygrothermal comfort
Does hygrothermal comfort depend only on thermal insulation?
No. It also depends on heat capacity, thermal phase shift, water-vapour permeability and wall surface temperature: parameters that must always be considered together.
Does hemp and lime eliminate the risk of condensation?
No. No material on its own eliminates risks arising from design errors. Correct management of the layer build-up, ventilation and thermal bridges remains essential.
What is the difference between steady-state U-value and dynamic behaviour?
Thermal transmittance describes simplified conditions; dynamic behaviour considers actual variations in temperature, humidity and solar radiation throughout the year, in accordance with technical criteria also referenced by the CTI – Italian Thermotechnical Committee.
To explore the complete range of hemp-lime systems, see the complete guide to hemp-lime thermal insulation or request the updated technical data sheets. For an assessment of your project, contact the TecnoCanapa technical department.
