What is the minimum number of straight lines required to make the given image?

Let's count the lines systematically by tracking their direction:
1. Vertical/Main Central Lines: There is $1$ main vertical line in the structure.
2. Horizontal Lines: There are $2$ clear horizontal boundary line steps.
3. Slanting/Diagonal Lines: * Left side slanting lines going downwards and upwards forming triangles = $5$
* Right side slanting lines forming matching intersections = $5$

Summing them up: $1+2+5+5=13$ straight lines.