A dormer is a window that sticks out from a sloped roof, creating a small room or extra space in an attic. If you've seen a house with windows poking through the roof instead of sitting flat in a wall, you've seen dormers.

Dormers serve two purposes: they let light and fresh air into attic spaces that would otherwise be dark and stuffy, and they create more headroom so people can actually stand up and move around. Without dormers, many attics would be too cramped and dim to use as bedrooms or playrooms.

You'll see them on cottages, farmhouses, and older homes where families wanted to squeeze extra living space out of their houses without building an entire new floor.

Architects design dormers in different styles: some have peaked roofs that match the main house, while others have flat tops or curved shapes. A dormer creates its own little roof within the bigger roof, which is why it can look like a miniature house perched on top of the main building.