The fiscal deduction provides a tax saving of the 36%, for a maximum expenses of 5000€. the deduction is applied for every single property, so whom has two houses, will get the Bonus for two times.
For example: if the spending is 10000€ (for two houses), the overall deduction will be an amount of 3600€. This amount will be spread over 10 years.
The payments have to be documented and traceable via bank transfer, already used for every general fiscal deduction.