Since chances are that none of your property improvements are 100% business use, the safe harbor election is just not an option.
Now if the building is physically separate from the residence, you could be claiming that building all by itself at 100% business use. If this is the case, then safe harbor is an option as all property improvements to "THAT" specific building would also be 100% business use.
Property improvements are entered in the Business Assets section and will be depreciated over 39 years. Make sure you indicate the correct business use percentage of the asset too. Some examples.
Example 1: You have a room in your house designated as a home office. It occupies 5% of the floor space. Therefore the property is 5% business use.
You put a new roof on the house at a cost of $10,000. Enter that new roof as a business asset and indicate it's 5% business use.
You installed new windows throughout the entire house at a cost of $3000. Enter it in the business assets section and indicate 5% business use.
Example 2: You installed new windows throughout the house at a cost of $3000. With a total of 30 windows replaced that's $100 per window. Three of the 30 windows were installed in the home office. You'll enter two asset entries for this.
One asset entry will be for $2,700 for the 27 windows installed in the non-business portion of the house, and business use percentage is zero percent. Another asset entry will be for $300 for the three windows installed in the home office room, and business use percentage for those three windows only will be 100% (one hundred percent.)
In my personal opinion, things will be simpler for you in the long run if you enter the windows as a single asset with 5% business use.
