@RaifH Take a look at pub 936 page 9 top of 3rd column, 2nd paragraph
The cost of building or substantially improv-
ing a qualified home includes the costs to ac-
quire real property and building materials, fees
for architects and design plans, and required
building permits.
Since the property is adjacent to the main home, would this not qualify as acquisition debt secured by the main home since the property becomes "a part of" the main home and the property the main home is built on? Or is this a grey area open for interpretation?
