The Tye family recently had a water leak in an investment proeprty, due to heavy rain back in the spring. Here in our region, most exterior doors open inward. Door that open inward fit inside the frame, rather than covering the outside of the frame. On this property, there is no porch cover or awning, to protect from rain. So with the heavy rain hitting at the perfect (or imperfect) angle and with enough pressure, water actually pushes through the door seal. This resulted in thousands of dollars in damage to our flooring, baseboards, etc.
We realized that we either needed to add a porch awning, or a storm door. The storm doors hinge outwards, and completely cover the opening, rather than fitting inside of it. We decided on the storm door, as it was less expensive, AND it’s enjoyable in two ways. One can leave the main door open and let light in through the storm door, or when the weather is nice they can actually pull down the screen (not all models have this feature. I would recommend hiring a professional (or handyman) to install these, as they can be very complex. I learned this the hard way on my own house 10 years ago! Another thing to point out, if you purchase one with a screen, make sure it’s a pull-down screen, rather than removeable glass. On the removeable glass models, you have to remove the ENTIRE piece of glass and store it somewhere. That would be very inconvenient. So to summarize, you should not need a storm door unless you have an exterior door with no porch cover or awning.
Here is a link to the door we purchased at Lowe’s!