Confusing question on home equity...

[Buck Dabill]

I have purchased 6 properties in the last few years and held them as long term rentals. I purchase the properties and fix them up using a line of credit and then refinance them paying off the credit line. I bought a property for 45k and fixed it up for 100k, so i am into it for 145k. I have only worked with one bank on all of my deals. This Bank is saying I do not have enough equity left in the property to refinance a mortgage for 145K and get my 100k line of credit back to use on the next project. The property is worth 300k. They are saying because the property is a rental they only use a cap rate to define its worth not what it could sell for so they are only giving it a worth of 109k. Do all banks value single family properties this way? I should add it is currently renting at 1,550. I have 6 properties that have a total value of 960k if I were to sell them, but they are only saying they are worth 688k in their book. They will lend up to 75% of the 688k which is 516k. My most pressing issue is a property I just bought for 256k that I need 50k in order to fix up so I can turn it into my first STR. I would appreciate any advice you might be willing to give on my situation.