Is it illegal to install aluminum alloy doors in the owner's garage?

There are illegal buildings and illegal buildings in the legal sense, and there are differences between buildings and structures. Installing aluminum alloy doors is definitely not an illegal building in the legal sense.

However, the scope of illegal buildings in our daily spoken language is much wider, such as building kennels, digging swimming pools, changing the external walls of buildings and adding billboards. We all call it illegal building.

As far as the case you mentioned is concerned, the key depends on whether the property management agreement of the community has made relevant provisions on the change of the external wall and appearance of the community. Generally speaking, many old residential areas do not have the regulations of installing iron gates, closing balconies and security window, so from the outside, the whole residential area is uneven and colorful. However, in order to avoid this kind of chaos and maintain the high-end appearance image of the community, new commercial housing often has relevant restrictions. I suggest you consult the property company that manages the community on this matter.