[MargaretR]

I have been websearching again and found that navvies built 'sod huts'
Towards an archaeology of navvy huts and settlements of the industrial revolution | Antiquity | Find Articles at BNET

Little is known in detail about the construction, use and frequency of the sod hut. It seems to have been used when no other accomodation was available or where the individual navvy was particularly independent (Coleman 1981: 80-85; Sullivan 1983: 73-80). It was a small, self-built dwelling constructed of locally available materials such as turf, timber and tarpaulin.

and this amusing account of how they lived
http://www.victorianweb.org/history/...ullivan/4.html