A penthouse.

Pentise, Penthouse] Lean-to building or covered passage or gallery. (Wood, Margaret. The English Medieval House, 413) A covered way with open sides to enable people to walk between separate buildings in the dry when it is raining. (Beresford, Maurice and Hurst, John. Wharram Percy: Deserted Medieval Village, 138) Related terms: Pent Roof

a passage way along the side of a building formed by a single-pitch roof supported on corbels