Pusey, Lamont, and some parts of the Houghton stacks are problematic work and storage areas for winter time RH (December through February). This is when the RH is below 30% and the physical changes that can happen are irreversible.
Some vellum printed books have been stored temporarily in the Hofer space during these times. But the Manuscript section follows a different practice. Since it isn't always possible to avoid working on or storing material in the affected areas, all codex manuscripts with vellum pages are by default measured for phase boxes. While awaiting boxes, they are compressed upright with bricks, or flat with an appropriate amount of weight. Single leaves are foldered and stored in flat boxes in individual folders with a moderate amount of weight on top, in the form of archival boards, either on top or interleaved when necessary, though they could also be stored in phase boxes with a build-up. Boxed collections are slightly less at risk because they provide weight for each other. Take care to keep individual leaves weighted with at least a prefab, for example, until they are sent for end-processing.