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Building a Castle: Flooring

The size of a Great Hall was limited by the length of beams the carpenters could get from available trees, for the roof and the floor. Some great towers were built with in internal crosswall which enabled each side to be roofed and floored independently. Upper floors were supported by pillars in the rooms beneath.

Joist holes Chepstow Castle

Masons and carpenters worked closely together. In ruined castles today you can see the joist sockets in the walls for the supporting beams. The walls were built to the right height and the joists put in place. Then the walls were continued, building them around the joists. In some cases there was also a spine beam running at right angles.

Joist holes Nunney Castle

Another problem was the weight of such huge beams. Without modern machinery, how did the builders lift them into place? The floor of the Great Hall at Guédelon is supported by six oak purlins each 7 m (23 ft) long. Each beam weighed about 600 kg (1,300 lbs), had a cross section of 35 cm sq (3.5 in sq) and needed to be raised 4.5 m (15 ft) above the ground to be fitted in place.

Treadmill winch

The normal device for lifting was the treadmill winch, but it was feared these joists would be too heavy and the winch would not allow for accurate placing. They came up with a different method. The ground floor walls were raised with a sloping top, the western end at first floor level and the eastern end at ground level, allowing the joists to be rolled up to first floor height by a team of men. All the joists were raised to first floor level at the western end and the walls were completed to first floor level so the joists could be rolled into place before the build continued.

Floor joists Guédelon Castle

After installing the joists, the carpenters laid oak laths between them and covered them with 20 cm (8 in) of earth, tamped down and level. On top of this 5 cm (2 in) of mortar was laid and then the tiles. At Guédelon, 4,000 kiln-fired tiles were needed to make a beautifully level, tiled floor.

[adapted from The Medieval Castle Haynes Manual by Charles Phillips]

Ann Marie Thomas is the author of four medieval history books, a surprisingly cheerful poetry collection about her 2010 stroke, and the science fiction series Flight of the Kestrel. Book one, Intruders, and book two Alien Secrets, are out now. Follow her at