“Clerestory” seems to be yet another arcane bit of church-speak or architect-speak.
It’s actually pretty simple:
it’s just what it says when pronounced correctly – [KLEER] + [STAW] + [REE];
a clear “layer” in the wall
to let in the light .
The original church was built with no high level windows. These were added sometime in the 16th century. It is likely that this major piece of work was done at the same time as the church was extended to the east.
The original steep single-pitch roof was flattened out somewhat and the signs are that the walls above the arches that carry the roof beams were raised slightly to give better space to fit this row of windows. At the same time, the outer south aisle wall was lowered considerably, causing the existing south windows to be truncated. The window tracery has been modified, but the evidence of this work can be seen in the sides of the windows. Originally with a Gothic pointed top, they have been sliced off to accommodate stone lintels that support the new roof.
If you move outside the church and look up at the tower wall outside, you will see the moulding that marks this previous and steeper roof line.
We have, then, three major pieces of work, all of which are dated in the 16th century. The roof was made less steep; the South Aisle roof was lowered and the east end of the church was very significantly lengthened. In addition to this, the long-time owners of St Andrew’s, the Priory at Bolton Abbey, was dissolved by Henry VIII in 1540.
How do these all fit together? Was all of the work done as a single major project? Was the work done by the Priory before 1540? (If so, are there any Priory records to show it?) Was the work done after 1540, when the patronage of St Andrew’s passed to Christ Church, Oxford? (If so, are there any Christ Church records to show it?)
All these questions may provide rich research ground. But what we can tell is that these Tudor builders made a dramatic difference to a gloomy and dark interior with the introduction of our new clere-story windows.