Building extensions taken to extend much more than an inch? (4)

I believe the answer is:

ells

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'building extensions' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for ells that I've seen before include "Former length measures" , "Cloth measures" , "Lengths of cloth" , "Old English lengths" , "Extensions at right angles to the main building" .)

I've seen this clue in The Times.

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