The phrase "up to the rafters" typically means that a space or room is completely filled or overflowing with something. Antonyms for this phrase could include "empty," "bare," "sparse," "unfilled," or "desolate." When something is "up to the rafters," it may feel cramped or cluttered, so the opposite could be described as "roomy" or "spacious." Additionally, if a room is "up to the rafters" with noise or activity, antonyms could include "quiet," "still," or "tranquil." Similarly, if a person's emotions are "up to the rafters," antonyms could include "calm," "placid," or "at ease.