> 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

<figure><img src="/files/uMoEc4RhCBuIlbnwhNfC" alt=""><figcaption></figcaption></figure>

## 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).&#x20;

## 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.&#x20;

### 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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