St Agatha's walls are almost entirely Norman, from the early 12th century as shown by a small window in the south wall of the nave which has its round head carved out of a single stone. The 13th century alterations consisted mainly of improving the light by inserting lancet windows. Two lancets were punched through the east wall of the chancel instead of the more usual three, a feature of other churches in the area such as Barlavington. 
The ceilings have been plastered but retain many of the original beams. The middle beam in the nave supports a queen post with wiggly braces.Another unusual feature is the porch, which is to the north, probably for the convenience of the residents of the manor house.
The only significant damage was caused by a restoration in 1906 when the belfry was enlarged (though a tall spirelet was later removed and replaced by a cap closer to the shape of the original). The architect also repointed the walls with harsh cement that clashes horribly with the earlier work.
