Yes, you are correct that the land is 28.5% and that out of the $125,000 purchase price, 28.5% of that is allocated towards the land.
The $2,150 settlement charges are also prorated in the same way.
However, the $10,739 for the improvement is solely added to the home. Your basis for depreciation is 71.5% of the house cost and closing costs plus the amount of the improvement.
This is what TurboTax is actually doing:
$30,000 Land Value / $105,100 Total Value = 28.54424%.
Your total value is cost, plus closing costs plus addition.
