Raising Second Floor Sunken Floor

Old 04-14-21, 11:12 AM
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Question Raising Second Floor Sunken Floor

Beams supporting sunken floor

sunken floor (plywood sheets are covering an opening)

I have a sunken living room on a second floor
The room is approximately 15'X12'
The current floor is 3/4 plywood lain over 16'X4'X8' beams spaced 16" apart.
The beams are open and visible from the first floor. See photo
I want to raise the floor to the height of the floor on the rest of the second floor by building on top of the existing sunken floor.

Are those beams large enough to support the joists and decking of another floor?
If so, is there a preferred direction the new floor joists should run i.e. on top of and parallel to beams or perpendicular?
In light of weight distribution should there also be consideration for the spacing of the blocking to aid in weight distribution?

Old 04-14-21, 03:18 PM
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When you think about it your not adding all that much weight per sq ft.

No more than say a nice big pool table or set of heavy furniture.

I would go across the existing joists!
Old 04-14-21, 06:31 PM
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Yes, you can add the new floor on top of the old. I would put down felt paper first, just to help cut down any noise if anything would rub due to deflection. I would also put the new joists parallel to and directly on top of the existing joists, so that the weight is being put on the same load bearing walls as the existing joists. The 3/4" subfloor goes perpendicular to the joists and should be tongue and groove... and should be glued (PL 375 or PL400) and screwed down with 2" deck screws.

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