Blueprints include construction drawings, construction plans, building plans, housing plans, floor plans, and working drawings. The term "blueprint" comes from the fact that early drafts were printed on paper with only blue ink, to avoid contaminating the white space with black lines. The most common type of blueprint is a construction drawing. A construction drawing shows the exact details of a building or other structure as envisioned by the blueprint's author. The drawing may show the actual materials used in the project, such as wood for doors and windows, brick for walls, and steel for beams. It may also show the arrangement of rooms and amenities, such as bathrooms and kitchens. Last, but not least, it may indicate any changes to the original design made during the planning process. A construction plan is similar to a construction drawing, but it includes information about how the building will be constructed from the ground up. For example, a construction plan might show the layout of the foundation, the plumbing, and heating systems before any walls or ceilings are installed. Building professionals call this type of drawing a "floor-by-floor plan." A housing plan is designed to help builders construct homes that meet federal affordable housing requirements.