32 Frederick Street

The graphic on the left shows the upper floor construction (to some extent this is an informed guess). In summary:

• The joists are probably at 400mm centres (16 inches)
• Joists are built-in to the party walls - this may present problems in terms of fire protection and sound insulation but it does ensure the joists don't get wet. In better quality construction the joists were sometimes supported on wrought-iron brackets.
• Joists are also supported on internal loadbearing walls. 
• The joists normally run the shortest distance across a room.
• The joists are not built-in to hearths but trimmed around them.
• Strutting stops the joists from twisting.
• Most Victorian floors were originally covered with square edged boards.
• Ceilings were usually timber lath and plaster (right-hand photo).

To stop the joists from twisting or warping (and possibly damaging the ceiling finish) it's usual to find a line of strutting fixed at right angles to the joists.  Strutting also helps to ‘tighten up’ a floor, thus reducing ‘bounce’. The struts can form a herringbone pattern or can be  ‘off-cuts’ of timber;  usually staggered so that they can be easily nailed to the joists. 

The most complex part of the upper floor is the trimming around the openings. At Frederick Street the floor is trimmed around the stairs and around both chimney breasts. The construction around the chimney is design to prevent timbers catching fire. You can see from the left-hand graphic and the floor plan (top left) that there is a trimmer joist running parallel to the front of the hearth. This supports the trimmed joists, the trimmer itself is supported by the trimming joists. The hearth is usually supported by a half-barrel vault or brick infill. The photo on the right shows a similar detail on another late Victorian property (looking from below).