Getting 4th 4 family financed.

[Jennifer McCurrach]

My husband and I live in a house (almost 4 years) on a 30 year mortgage. We have 2 four family buildings (purchased in '10 and '14), and we just entered a contract to buy a third 4 plex. We did 20% down on our primary residence, and 25% on all 3 rental buildings. This last purchase will eat up most of our cash reserves for the down payment. Just yesterday, I got an inside call about a building near one of ours that is going to sell, and I just cannot pass it up. It is also a 4 family. Now, for my question: How do I get the money for the down payment and have the reserves required for owning 4 properties? Can I do a HELOC on my primary? Do I dip into retirement? I've read conflicting info about the ability to borrow against IRA or 401k. Please help!