Where I'm from houses or house entrances next to each other would be numbered either 9+11 or 9A+9B. 9+9a looks so asymmetrical.

by moschtert

19 comments

  1. the house was probably split in two seperate houses at some point and they had to give the new house the “a” at the end of the number

  2. Not uncommon in Germany to have 9a next to 9 (rather than 9a + 9b).

  3. To go for 9+11 or 9A+9B, you need to know in advance that the house will be split.

    If you don’t know that in advance, 9+9A is the only thing you can do if you want to avoid renumbering original house 9.

  4. If it was planned like this from the beginning, numbers would have been 9 + 11.

    If it would have been redeveloped and house no. 9 was replaced by two new houses, those two would become 9a + 9b.

    However, if house no. 9 stays as it is and a new one is built e.g. in its backyard, that one becomes 9a and 9 stays as it is.

    Renumbering existing houses is usually avoided since that means quite some inconvenience for the people living there as they would have to change their address everywhere as if they had moved.

  5. Happens when old houses have huge yards, so they split the plot to build another house, so that house is 9a because all other numbers on the street are taken.

  6. In the beginning, there were house 9 and 10. Then another house was built in between, that is 9a.

    EDIT: in most German cities, the new house will have been built between houses 9 and 11 with number ten on the opposite side of the street, but you get the gist.

  7. This is quite common in Germany. Normally it goes like: House number nine had been there already, so did numbers seven and eleven. (The numbers on one side of the street are normally all odd or all even) Then they build a new house (probably in the backyard of nine) and needed a number for it. 7,9,11 already were given. Renaming 9 to 9a would cause confusion from people still using the old address. So number 9 stayed number nine and the new house became number 9a.

    If new houses are built and letters shall be used (semi detached houses sometimes have that although most houses use numbers only) they typically are named 9a, 9b,… Without having a separate number nine.

  8. Usually, the story behind it is that first there were the houses 7,9 and 11. Then a new house was built between 9 and 11 or somewhere in the number9 plot, but they did not want to change 9, so the new house is called 9a. Or house 9 got an additional apartment.

    If it is a building complex where the houses are all built at the same time, they get called 9a, 9b, 9c from the beginning.

  9. Normally:

    One side of the street gets odd, the other even numbers.

    The letters are used, if you hat the houses: 5, 7, 9, 11, 13 and then build a new house between 9 and 11. So you can number the new house without renumbering all the other houses.

    Another reason can be, that you have the numbers 5, 7, 9, 11, 13 directly at the street and behind house 9 is another house build, then this house gets number 9a.

  11. Linear equation. You just need to find a solution for

    9a + 9 = 0

    9a = -9

    a = -1

    So, here it is: the actual house number is -1

    If we’re talking about Complex numbers, which makes a lot of sense in areas, you could also interpret -1 as i².

    So take the Imaginary Lane and turn 90° to the left, which is pretty much the geometric meaning of multiplying i*i

  12. This means the numbers have historically grown. At one point in the past there where all nice numbers 9,10,11 etc.

    Then houses got added and removed.

    If you need an additional number between 9 and 10 you would use 9a. In this case 9 and 9a seem to be two houses with a shared small accessway, probably build on the side of the former number 9 and the sign makes you aware of that accessway. 9+11 is similarly a shared access for number 9 and number 11 (number 10 is probably on the other side of the street)

    Sometimes houses are merged and keep multiple numbers.

  13. This derives from the numeration of the building ground. In this case, there was once a house with the number 9 which sat on a quite large piece of property. To the left and to the right of it were numbers 7 and 11. Then, this property was split into two and a second house was build. This new house then becomes the number 9a, since the other numbers were already taken.

    Especially in the outskirts of cities and smaller towns, houses had quite large lots since people used to grow food and sometimes even held a small number of animals there. Later these were split into smaller lots.

    A friend of mine once live in an area where a large former industrial size was split into numerous lots. His house-number ended on “t”.

  14. It’s a Math Problem. You have to Solve it to get the House Number.

  16. You wouldn’t change all numbers when on a lot a second house is built… Or what would you name a additional built house on a reliably long and high number street like Venloer or Aachener in Cologne (house numbers up to the hundreds and thousands) when hypotetically you built a 2nd house on the 55 lot would you give it 1055 for example… or would you renumber all houses?1

  19. I live in a 32a address, no wonder the mail can’t find me.

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