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Vapour Resistance

Reference data and engineering information about vapour resistance for electrical applications.

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Overview

Engineering reference data for Vapour Resistance in electrical engineering.

Key Formulas

Ohm's Law

V=IRV = IR

Voltage = Current × Resistance.

Power

P=VI=I2R=V2/RP = VI = I^2R = V^2/R

Electrical power.

Energy

E=PtE = Pt

Energy = Power × Time.

Variables

Symbol Description Unit
VV Voltage V
II Current A
RR Resistance Ω
PP Power W

DataTable

Definitions

Vapor Resistance (Vr): The total resistance a material offers to the diffusion of water vapor, measured in N·s/kg. It is a property of the material layer as a whole.

Vapor Resistivity (νr): An intrinsic property of a material that describes its resistance to vapor diffusion per unit thickness, measured in N·s/(kg·m). It is a key parameter for calculating the total resistance of a layer.

Practical Insights

The vapor resistance of a building assembly is critical for managing condensation risk within walls, roofs, and floors. Materials with very high vapor resistivity (like aluminum foil) act as vapor barriers, while materials with low resistivity (like glass wool) are vapor-permeable.

The formula Vr=t⋅νrV_r = t \cdot \nu_r shows that total resistance increases linearly with material thickness. When analyzing moisture risk, the vapor resistance values of individual layers are summed to assess the overall assembly's resistance profile.

References