> For the complete documentation index, see [llms.txt](https://docs.betterbuilding.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.betterbuilding.io/user-guide/workflows/moisture/internal-surfaces.md).
# Internal Surfaces
## Convection Method
Configure the Convection Method to determine fixed or dynamic inputs.
### Fixed value
Configure a Convection Coefficient W/(m² K). Wall Default 2.5 W/(m² K).
## Vapour Method
Configure the Vapour Method to determine fixed or dynamic inputs.
### Fixed value
Configure a constant Vapour Transfer Coefficient kg/(m² s Pa). Wall default 2.57e-8 kg/(m² s Pa).
## Coating Method
A vapour-retarding coating is a liquid-applied material used to slow down or limit the movement of water vapour through building surfaces like concrete slabs, walls, or thermal insulation. It prevents moisture from entering structural cavities and causing condensation, mould, or material decay.
### None
Configure a vapour-retarding coating on the exterior surface. Default = no coating.
### Fixed sd
Configure a vapour-retarding coating on the exterior surface. Select from dropdown or specify specific value.
## Solar Absorptivity
Configure the Short-wave (solar) absorptivity of the exterior finish. Solar absorptivity (or solar absorptance) is the fraction of total incident solar radiation absorbed by a material, expressed as a decimal value between 0 and 1. Default 0.5, representing a mid coloured wall.
## Long-Wave Emissivity
Configure the Long-wave emissivity, a measure of how efficiently a surface emits thermal or infrared radiation compared to an ideal blackbody, typically ranging from 0 to 1. Default 0.90.
---
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