Have you ever wondered why so many large chain stores have two sets of doors? No, it is not just to store shopping carts.
Where I live, any home that is around 100 years old (that hasn't seen any renovations) will very likely have two front doors. Putting it simply, you open one door, step into a small space, and there will be another door in front of you.
(Image Sources: Image 1 | Image 2)
The space goes by many names, including: arctic entry, mud room, breeze room, vestibule, airlock, foyer, and more. For sake of simplicity, I am going to call them "entry vestibules."
Entry vestibules create a buffer between the outside and the inside of the building, preventing drafts. This can help greatly with temperature regulation in both the winter cold and summer heat. I can't find number details on energy saving, but the fact that large chains still build them may hint of their importance for money-saving.
In homes, this space also typically serves as the mud room ( a place for shoes and jackets).
In the name of "first impressions," and open concept designs, vestibules are often the first thing to go during renovations, and I think that's a real shame.
I was going to ask what you call "the area traditionally called a porch" until I discovered.....calling the sitting area in front of a house a "porch" started in the southern US.
Porch predates America entirely, being a common structure on medieval churches and such.
Right! I didn't know that until I looked it up to include a picture and read the Wikipedia page. I've never heard it used in any other context than a front deck