Understand the original logic
Before adding anything, map the proportions, circulation and daylight of the existing house. The strongest extensions tend to respond to what is already there rather than treating the old building as an obstacle.
New does not have to imitate old
A contemporary addition can sit comfortably beside a period house when scale, rhythm and material are considered carefully. Copying historic detail is only one option — and rarely the most interesting one.
Plan beyond the planning application
Permission is a milestone, not the finish line. Structure, drainage, thermal performance, lighting, joinery and construction sequencing all need space in the programme after consent.