You only have to claim depreciation if you choose to use the regular method for your home office. If you choose the simplified option, you don't.
If you want to use the regular method, you would only take 50% of the adjusted basis of the house, since that is all you own. You would then prorate the square footage of the space of the home office vs the square footage of what you own.
Simplified Option
For taxable years starting on, or after, January 1, 2013 (filed beginning in 2014), you now have a simplified option for computing the home office deduction (IRS Revenue Procedure 2013-13, January 15, 2013). The standard method has some calculation, allocation, and substantiation requirements that are complex and burdensome for small business owners.
This new simplified option can significantly reduce the burden of recordkeeping by allowing a qualified taxpayer to multiply a prescribed rate by the allowable square footage of the office in lieu of determining actual expenses.
Regular Method
Taxpayers using the regular method (required for tax years 2012 and prior), instead of the optional method, must determine the actual expenses of their home office. These expenses may include mortgage interest, insurance, utilities, repairs, and depreciation.
Generally, when using the regular method, deductions for a home office are based on the percentage of your home devoted to business use. So, if you use a whole room or part of a room for conducting your business, you need to figure out the percentage of your home devoted to your business activities.
