Thermal Transmittance in Membrane Structures: Fundamentals and the Physical Limits of the Single-Layer Membrane

Technical Note TN01 establishes the thermal-physics basis for the assessment of single-layer membrane envelopes. It examines thermal transmittance using the resistance framework of EN ISO 6946:2017, with particular attention to the unusually high influence of internal and external surface resistances in very thin membrane constructions.

The study separates conductive resistance of the membrane from convective and long-wave radiative surface heat transfer and examines the effect of surface emissivity under defined steady-state boundary conditions. The internal surface resistance is explicitly resolved using the relations of Annex C of EN ISO 6946, while the conventional external surface resistance is retained for the numerical reference cases.

A parameter study compares a conventional-emissivity surface with representative low-emissivity cases for roof and wall configurations under winter and summer conditions. The results show that reducing the internal surface emissivity can substantially reduce calculated thermal transmittance, while also demonstrating the physical limits of improving a single-layer membrane without adding an insulating layer.

The note is intended as a transparent engineering reference for membrane structures and as a foundation for subsequent Technical Notes addressing low-emissivity surfaces and multilayer membrane envelopes.