The general upgrade of open halls to retrofit chimneys started approximately between 1550-70 and by the early 1600's building houses with a chimney was fairly standard practice but the statistics on this topic are still in the process of being researched and compiled following dates that are arising from the dendrodating of more houses / cottages. The date of inserted floors will most probably coincide with the date of the chimney build.
Early houses were sometimes built with smoke louvres which sat on top of the rafters creating a little elevated roof area. Almost none of these smoke louvres have survived but from time to time remnants are encountered in a smoke blackened attic.
Sometimes a long (6ft) clay chimney pot was clamped between a pair of rafter couples above the fire with this pot passing through the thatch.