On Thursday, 14 March 2019 18:51:13 UTC, DerbyBorn wrote:
Why is the bit that usually has the kitchen and small back bedroom at a
lower level than the rest of the house? Was it just cost saving or was it
to so with roof construction

It's to do with natural daylight.
Terrace houses only have windows front and rear.
To illuminate them, windows had to be tall so ceilings also have to be high.
Less important in kitchens.
Even more so in "back to back" houses.

You also find this in buildings with very large rooms. Eg"Stately homes".

All to do with there being only very limited artificial lighting.