We introduce HouseCrafter, a novel approach that can lift a 2D floorplan into a complete large 3D indoor scene (\eg, a house). Our key insight is to adapt a 2D diffusion model, which is trained on web-scale images, to generate consistent multi-view color (RGB) and depth (D) images across different locations of the scene. Specifically, the RGB-D images are generated autoregressively in batches along sampled locations derived from the floorplan. At each step, the diffusion model conditions on previously generated images to produce new images at nearby locations. The global floorplan and attention design in the diffusion model ensures the consistency of the generated images, from which a 3D scene can be reconstructed. Through extensive evaluation on the 3D-FRONT dataset, we demonstrate that HouseCrafter can generate high-quality house-scale 3D scenes. Ablation studies also validate the effectiveness of different design choices. We will release our code and model weights.