You can also deduct proportional utilities and other related expenses. I have never had a problem, but my accountant suggested that I take dated photos of the office, which clearly shows that it is solely a workspace. Don't know if that would help, but so far no problems, so I haven't had to find out. One downside is that when you sell your house, you will be liable for the deductions that you have taken for depreciation, which makes it less desireable to take the deductions in the first place, but if you are renting, it is much "cleaner".
Jessie