There are at least a dozen variants of stairs for residential properties. The most common are the straight staircase, where the steps are fastened in lateral stringers, the spiral or curved staircase, which turns helically at least once around its own axis, and the ladder staircase, where a beam supports the treads. In the living area, maple, beech, birch, oak, ash, cherry or walnut are popular because wood radiates warmth. Aluminum, concrete or galvanized stainless steel are especially suitable for modern buildings.