I do not remember my childhood home without the addition. I have clear memories of that addition being built. One: in basement, mom doing laundry, I was playing with older brother's mini-cement block maker ~ I thought those mini-blocks the coolest things. Mother scalded me, telling me not to play with it "might break it". The washer and dryer were on concrete floor, but I was sitting inside the doorway on a dirt floor.
The other: I was in the unfinished dining room looking through open floor boards to the basement. I vaguely recall being scared. I may have that memory mixed up with another. I would say "brother Richard snuck me into the room to show me", but it could have been brother, Robert. I remember riding tricycles around in the empty dinning room, with Richard.
My younger sister was born when I was 2-years, 9-months old. The house addition was built when she was born. She was born in June, so likely the new construction started spring that year. Or my earliest memories are from before I was three.