Can I elect 100% of new home office as 179 expense?

[Coleen3]

No. Your expenses are not eligible and real property isn't either. If you have a computer or other assets, do not include them in the home office. You can take a separate 179 deduction on those assets.

[DBinSD]

I classified the office as "Qualified improvement property" because my home office was added in the basement after the house was constructed. Then TurboTax gave me the option of "I'll deduct the full value of the item this year". There's nothing in the Help that explains when this would not be allowed. Why would TurboTax allow this?

[Coleen3]

There is an improvements election. It is usually associated with rental property.
Improvements Election
This election is an option you can take each year that lets you write off some building improvements as expenses instead of assets. Here are the rules you need to meet to take this election:
• Your gross receipts, including all your other income, are $10,000,000 or less.
• Your eligible building has an unadjusted basis of $1,000,000 or less.
• The cost of all repairs, maintenance and improvements is less than or equal to the smallest of these limits: 

• 2% of the unadjusted basis of your building or
• $10,000
This election for building improvements is called the Safe Harbor Election for Small Taxpayers. If you decide to take this option, a form called Safe Harbor Election for Small Taxpayers will show up in your tax return. This election will apply to all your businesses, rental properties or farms.

[DBinSD]

The total cost for building my office was $9,590. Can I claim that entire amount as an expense in 2018?

[Coleen3]

Upon further consideration and consultation, this does not apply to you. First, the improvement is to your main home. An improvement to your home is not deductible. It does not become your home office until after the improvement has been done.

In addition:  Although you cannot deduct any depreciation or section 179 expense for the portion of your home used for a qualified business use, you may still claim depreciation or the section 179 expense deduction on other assets used in the business (for example, furniture and equipment) <a rel="nofollow" target="_blank" href="https://www.irs.gov/publications/p587">https://www.irs.gov/publications/p587</a>