You will be able to tell if the walls are built on top of the original boards by a simple bit of detective work - which way the boards run and wether they stop short of the wall for a start.
I'm fairly sure most floors layed are layed over the existing subfloor with new skirts and undercutting the door frames - it helps if you lay the new boards in the opposite direction to the original boards.
Portanailers are very popular, simple to use and reliable when you get near the edges and theres no room to swing the hammer drill pilot holes and hammer by hand at an angle through the tounge and when thats not possible pilot and top fix again using a single portanail.
A jigsaw and portanailer are the main tools you will need although a chopsaw will speed things up.
If you lay on the joists you will have more cuts/waste and will also lose the tounge and groove joint on the ends i would put plenty of pva wood glue under the butt joints else the may squeek move etc.
Glueing the tounge and grooves is not required if you are porta nailing.
I'm fairly sure most floors layed are layed over the existing subfloor with new skirts and undercutting the door frames - it helps if you lay the new boards in the opposite direction to the original boards.
Portanailers are very popular, simple to use and reliable when you get near the edges and theres no room to swing the hammer drill pilot holes and hammer by hand at an angle through the tounge and when thats not possible pilot and top fix again using a single portanail.
A jigsaw and portanailer are the main tools you will need although a chopsaw will speed things up.
If you lay on the joists you will have more cuts/waste and will also lose the tounge and groove joint on the ends i would put plenty of pva wood glue under the butt joints else the may squeek move etc.
Glueing the tounge and grooves is not required if you are porta nailing.