Tom helps homeowner Mark Andrews of Charleston, Massachusetts level an uneven concrete floor so that he can install hardwood flooring. Then Tom, Richard, Roger and Kevin ask, "What Is It?" in the Ask This Old House loft. Then, Richard shows homeowner Jenna Williams of Rex, Georgia a simple repair for a leaky water shut-off valve. Then, up in the loft, Tom teaches Kevin about air-compressors and how to select the right one for the job.