> For the complete documentation index, see [llms.txt](https://docs.altum.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.altum.ai/english/property-valuation-and-market/avm+-api/house-numbers-letters-and-additions.md).

# House numbers, letters & additions

### How to provide input on house numbers & additions?

As a general rule of thumb:

* A house letter is always a letter and always only 1 character.
* House number addition (toevoeging) can be everything in letters or numbers, and can be more than one character. Special characters are not accepted!
* The house number must only be a number.

Correct examples of house addition input to the API:

1. house letter: A, house addition: 02, `houseaddition` input as string "A02"
2. house letter: "'', house addition: 02, `houseaddition` input as string "02"
3. house letter: A, house addition: "'', `houseaddition` input as string "A"
4. house letter: "'', house addition: "'', `houseaddition` input as string ""
5. house letter: "'', house addition: 2B, `houseaddition` input as string "2B"


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