It’s not clear what you mean by cold storage. Like for food perishables? If the area under your porch is open and consistently cold, how do you plan to secure your food from critters, but still have it easily accessible?

Please define.. in my case, I built in a cold room under my house (root cellar)

I live in New England. The room, which did involve annoying zoning, did ultimately work. I made sure it was north/northeast in my basement. It will store vegetation I intend to grow/store for the foreseeable future.

To give you a better answer... where are you planning to build? (Growing zone wise...)

I have had such a room before and it is great for potatoes, onions and any canning you may do. I do recommend insulation, and ours had a couple small vents to the outside with screening to discourage “critters”. I am assuming this is a concrete basement space capped with a slab porch?

Our builder was originally going to fill in the "hole" for the poured foundation part of the front porch (that was going to have flagstone set in mortar and a concrete bed), so as said to put in a door into the basement, add some steel bridge decking and give us a room. We ended up putting out HVAC system in there and it's pretty good for wine too! (almost) FREE SPACE - how often does that happen?

We had a small section of front porch foundation made into a room accessible through the basement that we'll turn into a hidden storage room. The entire back porch foundation was opened for a storage room accessible through an exterior door that we'll use for unconditioned storage of outside stuff (patio furniture, small water craft).

I would and I did : ) , but I do a lot of canning and also have garden potatoes, carrots, and beets to store through the winter.

The foundation walls on ours are 10" thick under our front porch, Our builder installs ventilation pipes, then we will have a safe door into the room. This will create a huge safe for us and safe room too.

We are doing this too, but it’s not cheap. We had a structural engineer make a recommendation of which span deck (I can’t think of the technical term) we should use, and he also sized the steel beams required in the wrap around porch area. The materials are expensive, and we will need to frame and insulate the areas above grade to keep the area dry.