What is the main feature of platform frame construction?

The main feature of platform frame construction is that each floor is built as a separate platform. This method involves constructing the framing for each floor independently, using horizontal framing elements that rest on the walls of the lower level. This creates a strong, stable structure and allows for easier modifications or repairs over time, since changes can often be made on one floor without affecting the others.

Platform framing offers significant benefits in terms of construction time and cost efficiency, as builders can work on multiple levels simultaneously. The separate platforms help to provide lateral stability to the building, which can be advantageous in terms of structural integrity, especially in regions prone to seismic activity or high winds.

The other options describe characteristics that are not inherent to platform framing. While insulation might be a consideration in wall construction, it does not define platform framing. Continuous walls extending to the roof are more associated with balloon framing, and the use of steel beams for support is typical of different construction methods such as commercial or industrial buildings where larger spans are needed. Thus, the distinguishing feature of each floor being a separate platform defines this construction style.