Aspects are provided relating to additive manufacturing. In one aspect, an apparatus for producing a three-dimensional (3D) structure is described that includes a build chamber having a top portion with windows through which radiative energy from one or more sources is provided to the build chamber to produce the 3D structure, and one or more manifolds disposed within the build chamber. The manifolds are configured to perform a gas exchange within the build chamber, and each manifold is positioned above a region where envelopes of radiative energy from the one or more sources overlap. In another aspect, the manifolds are moved to a first position adjacent to the top portion of the build chamber during a first mode of operation and moved to a second position away from the top portion of the build chamber during a second mode of operation.