An apparatus and method for fabricating a three-dimensional object from a representation of the object stored in memory. The apparatus includes a build platform having a build gap defined therein. A base plate is initially supported along a lower surface of the build platform such that an edge of the base plate extends along and closes off the build gap. A powder delivery assembly is configured to supply powder to the build gap. At least one directed energy source is configured to apply directed energy to at least a portion of the build gap to form a layer of the three-dimensional structure. An advancement assembly configured to selectively engage with the base plate and/or the three-dimensional structure to hold the base plate and the three-dimensional structure in a fixed position during forming of a layer and to advance the base plate and the three-dimensional structure once the layer is formed.