also: とうおく
noun
rooftop structure; penthouse; elevator machine room
Refers to a small structure on a building's roof, such as an elevator machine room, stairwell housing, or a decorative tower.
ビルの塔屋にエレベーターの機械室がある。
The elevator machine room is in the rooftop structure of the building.
あのマンションの塔屋はちょっとした塔のように見える。
The penthouse on that apartment building looks like a small tower.
ペントハウス usually refers to a luxury apartment on the top floor, while 塔屋 is a structural rooftop enclosure, not necessarily living space.
Compound of 塔 (tower) and 屋 (roof/house), literally 'tower house'. The reading とうや is a standard on'yomi combination; とうおく is a less common variant.