Toilet Flange Extension

O' Great Plumbing Sages:

I'm about to install a new floor in my Mom's bathroom. Removing the old sheet vinyl will be near impossible, so we are going to install new underlayment and Durastone tile; this will raise the new floor about 1/2" above the top surface of the existing cast iron toilet flange. My uncle tells me this could cause the toilet to leak (even if I use a wax ring with a flange).

Is there such a thing as a "toilet flange extender"? If so, can they be installed on top of an existing cast iron flange?

There is and you may. However if it's only 1/2" you can stack 2 rings and get the same effect. Don't use the ones with the plastic horn.

Do you have access below as in basement or crawl space?

Yes, Redwood, I can access from the basement.