How to Widen a Staircase?

[Alison M.]

Hi all, I looked at a rehab candidate yesterday, an old rowhouse in NE DC. I like the property and will make an offer but I am stumped about how to estimate widening the staircase to the basement. First to clarify: by "wide," I mean the distance hip to hip as you start to go down the stairs, not the depth of each stair tread. This staircase was the narrowest I've ever seen - I am roughly 20" across at the hips and I was having trouble wedging myself down the stairs.

Any idea what is involved in widening a staircase like that? It hugged the party wall of the rowhouse on the right, and opened onto the basement on the left, as I went down.

Thanks! Alison