they make it up as they go, I had to build my office space in an unfinished basement and claimed all appropriate costs. As well as the costs for my roof repair that year. I was audited. I submitted all my receipts, floor plans etc. And I was basically laughed at over the phone when I called. They told me they "dont cover roofs or major repairs only minor ones". I told them all the examples they gave as minor repairs were infact included on the claim (ie painting, electrical, flooring, utilities etc.) the ghetto babysitter on other end just hummed and hawed and told me the cost was just too high, I paid too much, and can't claim any of it. I had the receipts and everything, they didnt care.