"Robert11" wrote

House is about 30 yrs old, original roof, and the foundation is 28' x 48'
Tri level (split type)
a. It's the original roof. Is it normal to place a second layer right
over
the first, or must
the original layer be removed first ? Why ? Cons ?

For a re-roof (second layer) application, the proper installation method is
called _nesting_, this is so your new shingles don't bridge the old.

Problem with re-roofing the design of structure like yours is being a
tri-level. Obviously it has side wall junctures where the lower roofs meet
the side of the main structure. In these areas you have what is called
_step flashing_, usually a 5"x7" aluminum or galvanized piece of material
bent at 2" to interweave with each shingle and 3" against the wall behind
the siding. You can't step flash properly putting the second layer on when
using the nesting method. Roofers will do what they call a double seal at
the juncture when they can't flash the area correctly. This in my opinion
is a poor way to install a roof.

It's normal to install a second layer on a tri-level, if you want
substandard workmanship.

Have the old roof torn off and done correctly.