Construction near power lines

[Marco Werner]

Hi all, 

I am looking to buy a property where I want to construct a 3-story ADU in the back of the property (replacing a garage).

The challenge I am running into is that there is a power line right behind the garage. How do I best figure out what is feasible in terms of clearance and its impact on the ADU construction? I have checked the maps of the department of power and water and the location of the power line is highly inaccurate. The maps show the power lines on top of the garage but I visited the site and they are behind the garage (although very close).

I won't go through with the deal if I cannot add at least 1000 sqft through the ADU construction.

Would love your thoughts on how I can best get clarity on this before making an offer or at least before closing.