Creating a website directory for URL structure-- Does it help SEO?

url structure and search engine optimization

[charlienichols]

Our company is creating a series of similar-themed websites. A couple are up and running, and it's recently come to our attention that URL structure has all of the pages off of the main page (ex: www.mainpage.com/subpage2). What we want is a hierarchical URL structure like the following: www.mainpage.com/subpage1/subpage2

Our website developer has informed us that, in order to do this with our current sites, we would have to set up a directory, and it would take several weeks and a lot of effort to reassign pages to parts of the directory...frankly, I don't fully understand the technical details, just that it's going to require a lot of time and effort.

So, for future sites, we have to weigh the cost/benefits of the time involved for creating this URL structure. I know there are some usability benefits, but, can anyone tell me: would this help with search engine ranking at all?