Need help understanding HELOC guidelines

[Clayton Warren]

Hi!  I have a home worth around 500k and debt on it of 275k. I am looking to purchase a second primary and would like to take a HELOC. 

I also have a renovation project that has debt of 205k.  My RE agent thinks there's no way I can get a HELOC since the balance of debt for both properties leaves me under 80 percent LTV (when you combine debts for both properties). 

I was unaware that they add debt you have in multiple properties.  I thought instead they look at DTI.  My current DTI is 28%.  Any advice would be greatly appreciated!!!