> 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/carbon/in-use-b4.md).
# In-Use (B4)
The In-Use Stages (B4) relate to the replacement of building components during the use phase of a building.
**B4 - Replacement**: This stage includes the energy and emissions associated with the replacement of building components during the use phase of a building. Building elements and systems may need replacement over the life of a building due to wear and tear, obsolescence, or damage.
The replacement of building components includes the production of new components (which would have associated 'upstream' emissions as outlined in stages A1-A3), as well as any emissions related to the removal and disposal of the old component and the installation of the new one.
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