This depends on the size and scope of the project. Generally speaking, the dust and dirt will be the worst in the initial demolition phase. Once we've got things stripped down to the frame, things will be fairly clean. Drywall installation and sanding will create a lot of very fine dust for a few days. We do our very best to seal off the rest of the house, but a little dust will always get through. It's a good idea to throw a plastic sheet over nearby sensitive items like electronics or fine furniture during this phase.