How can I raise a bonus room subfloor level with the adjacent floor?

Question

We recently bought a house and closed off upstairs was a bonus room which is over the family room on the main level below. The bonus room has a sub floor already in it, but it wasn't opened. So I cut the wall open at the end of the hall and put a door in. I now want to finish the room, but my question is, how is the best way to build up a floor.

When you go from the hallway into the unfinished room, there is about a 2" drop to the subfloor. I want to bring that floor up to level with the hallway.

Can I just cut 2 x 4s down and place them on top of the plywood subfloor and then put a new subfloor on top, or do I need to rip the old subfloor out and put some ripped down strips on the joists??

Answer 1

2 1/4 inches height difference could be made up with 2 x 4's on their side screwed in and glued over the existing joists and 3/4 OSB sub-floor on top. That will be 1/32 lower than the abutting sub floor when you take into account the actual thickness of the lumber.

You could use 2x2's, but often they're more expensive than 2x4s

Glue and screw everything to prevent squeaking.

The tricky bit will be the hardwood - carpet transition. From your photo, which gets pretty pixelated at high zooms, it looks like you have 3/4 inch hardwood. If there is still a tongue on it, you can buy a reducer piece that will drop the height down 3/4 of an inch smoothly. If it's a groove, you can buy a double tongue, which converts a groove to a tongue.

Otherwise, you may wish to have a threshold specially made for this purpose.