Given the following context:

Another major influence in his work was the rise of interest in vernacular architecture. By the time Douglas moved to Chester, the black-and-white revival using half-timbering was well under way, and Douglas came to incorporate this style in his buildings in Chester and elsewhere. The black-and-white revival did not start in Chester, but it did become Chester's speciality. The first Chester architect involved in the revival had been Thomas Mainwaring Penson, whose first work in this genre was the restoration of a shop in Eastgate Street in the early 1850s. Other early Chester architects involved in the revival were T. A. Richardson and James Harrison and it came to be developed mainly by T. M. Lockwood and by Douglas. Part of Douglas's earliest work for the Grosvenor family, the entrance lodge to Grosvenor Park, used half-timbering in its upper storey; this is the first known use by Douglas of black-and-white. Other vernacular motifs were taken from earlier styles of English architecture, in particular, the Tudor style. These include tile-hanging, pargetting and massive brick ribbed chimney stacks. In this style, Douglas was influenced by the architects Nesfield and Shaw. Douglas also used vernacular elements from the continent, especially the late medieval brickwork of Germany and the Low Countries.A characteristic of Douglas's work is his attention to both external and internal detailing. Such detailing was not derived from any particular style and Douglas chose elements from whichever style suited his purpose for each specific project. His detailing applied particularly to his joinery, perhaps inspired by his experience in his father's workshop, and was applied both to wooden fittings and to the furniture he designed. A further Continental influence was his use of a Dutch gable. The most important and consistently used element in Douglas's vernacular buildings was his use of half-timbering, which was usually used for parts of the building. However, in the cases of Rowden Abbey and St Michael and All Angels...

answer the following question:

Half-timbering is a component of what type of architecture? 

vernacular