Capital taxes on sales of house hack homes

[Michinori Kaneko]

Hi I wasn't planning on a house hack but I have a house that I'm considering renting out portion of it. It's not a multi family, it's a SFH. The question is on capital gains tax treatment when I sell the house down the line. I understand that when you sell your primary resident that you lived 2/5 past years you can get $500k deduction on your capital gains. I plan to rent it for few years then use the entire house as my resident when my kids get older and I need the additional space. My tax accountant told me that once I rent out a portion of the house that part becomes forever business property and while I can continue to take depreciation post rental period I will not be entitled to the capital gains treatment for that portion. Is this accurate? Is everyone that's house hacking paying capital gains taxes on portion they are not living in? Thank you for your help in advance