> 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/2d-building/drawing/horizontal-ceiling-tbc.md). # Horizontal Ceiling - TBC Projecting a roof is useful when a building’s thermal envelope extends beyond the ceiling line, either up to the roof line or into another zone above. This allows you to model more realistic volumes, especially in spaces like lofts, atriums or vaulted ceilings. ## Project a Roof To project a roof, first navigate to the zone you want to modify. This can be done for one or several zones, offering flexibility depending on your design. In the drawing space, select the zone and open the zone panel. Click on 'Using Envelope Settings' in the left panel and then navigate to the tab 'Ceiling'. Under ‘Ceiling Method’, choose the appropriate method for how ceilings are assigned. Select ‘Projected’ to extend the zone volume up to the external roof line. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.betterbuilding.io/user-guide/2d-building/drawing/horizontal-ceiling-tbc.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.