Mortgage insurance won't cover investment properties, so you need at least 20% down to secure traditional financing for them. If you can put down 25%, you may qualify for an even better interest rate, says Todd Huettner, a mortgage broker and president of Huettner Capital in Denver.If you don't have the down payment, you can try to obtain a second mortgage on the property, but it's likely to be an uphill battle.f you can put down 25%, you may qualify for an even better interest rate, says Todd Huettner, a mortgage broker and president of Huettner Capital in Denver. If you don't have the down payment, you can try to obtain a second mortgage on the property, but it's likely to be an uphill battle.