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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??enter image description here

  • What is your finish layer going to be? Carpet? Hardwood? Laminate? – Chris Cudmore Jun 10 '16 at 15:44
  • Also, what is the exact measurement? and what is it to the abutting subfloor? Or is it to the top of the finish layer? – Chris Cudmore Jun 10 '16 at 15:46
  • Is the subfloor securely attached? That's a lot of value in OSB and I'd reuse it if possible. It's also a lot of useless weight if you bury it. – isherwood Jun 10 '16 at 15:54
  • The room will be carpeted when finished. The hallway leading into the bonus room is a hardwood. The measurement from the top of the bonus room subfloor to the top of the abutting subfloor is 2 1/4" inches. Whoever build the house secured that subfloor down pretty good. It's nailed down, but also glued. I was concerned about the weight if I added another layer and consulted with an engineer. He didn't come look at it, but I sent pictures to him and explained what was going on. He seemed to think I would have a weight issue, but I certainly agree that's a big waste to cover it. – Howard Jun 10 '16 at 17:37
  • I meant the engineers seemed to think I wouldn't have a weight issue. – Howard Jun 10 '16 at 17:44
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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.

  • That's what I was hoping the answer was going to be. I thought I could do something like that, but wanted to make sure there wasn't any other hidden things I needed to know about when doing that. Thanks A lot!!! – Howard Jun 14 '16 at 18:31

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