110m squared for a house design does this mean just internal walls not external?
This is the question:
Produce plans, sections, elevations for a terraced dwelling, to fit inlcuding private open space on a site 20m long and 5.7m wide. your design should be about of 110m2 which will include a garden

You have to watch your terminology.
110 meter squared is NOT the same as 110 square meters or 110 m²
110 meter squared is a box 110 m by 110 m or an area of 12100 square meters.
A house of area 110 m² includes just the internal area in that number.
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The question clearly talks about the whole area covered. This means external walls
it means the external, plus the garden