In 1380 March 4, Gilbertus de Culwen, miles (Gilbert Curwen) was granted, by Richard II, (In year 3 of his reign) a Royal licence to crenellate Wirkyngton (Workington Hall)

"quandam domum per ipsum ut dicit apud manerium suum de Wirkyngton in Com. Cumb. juxta Marchiam Scotiae muro de petro et calce edificatam firmare et kernellare"

Granted at Westminster, by privy seal.

Original source is

• Calendar of Patent Rolls (1377-81) p447

(In fact, the original source given is usually a transcription/translation of what are precious medieval documents not readily availably. It should be noted that these transcription/translations often date to the nineteenth or early twentieth centuries and that unwitting bias of transcribers may affect the translation. Care should also be taken to avoid giving modern meaning to the medieval use of certain stock words and terms.)

Significant later source are;

• Emery, Anthony, 1996, Greater Medieval Houses Vol1 (Cambridge) p263
  King, D.J.C., 1983, Castellarium Anglicanum Vol1 (London: Kraus) p100n74
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p207-8, 418

More details about licences to crenellate can be found here.

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