> 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/driving-rain.md).

# Driving Rain

<figure><img src="https://2129322768-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FfKJnzF2TwHA3APPbiCpF%2Fuploads%2F6Wi2DT4X8t4KnqP42ZNE%2Fimage.png?alt=media&amp;token=d1d6c079-cf3b-42f2-86cd-a01c0904703b" alt=""><figcaption></figcaption></figure>

## Water Sources

Deposit a moisture or air-infiltration source into cells of the construction

### Rain

Configure the fraction of rain deposited anywhere across the entire construction. Default 1% on the water control layer.

### Fixed Source

Configure a Fixed Source kg/(m² s) water deposit anywhere across the entire construction.&#x20;

### Air Infiltration

Configure a Air Permeability (q50) m³/(m² h) rate to assume air exfiltration anywhere across the entire construction.&#x20;

## Exterior Rain Exposure Factor

Configure the exterior rain exposure factor that measures how much wind-driven rain hits a building wall. It depends on local weather, surrounding terrain, and building shape. Default 0.5.

## Exterior Rain Deposition Factor

Configure the exterior rain deposition factor that defines the ratio of wind-driven rain hitting a specific building facade compared to the unobstructed free-wind rain. Default 1.0.

## Exterior Rain Adhering Fraction

Configure the exterior rain adhering fraction (also called the rain reduction factor or rain water absorption factor) is the percentage of wind-driven rain hitting a building surface that stays on the wall to be absorbed, rather than splashing or running off. Default 0.7.


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