Shimming – How to Shim Sliding Patio Door Frame from One Side

Does the sheathing connect to the top plate securely? If not, because of the shims, you will need to run screws from below through the lower top plate. You could use long hurricane clips instead.

Photo courtesy HD Supply

I have seen long screws run through both plates from below, just like you have from the top, just run them in.

I'll make some assumptions in an initial answer and revise if needed.

• Your joists are sagging due to the weight of the brick wall.
• Your flooring (subfloor and possible finish floor) are warped into a channel as well.
• You are not trying to save hardwood or other finished flooring.

Here's what I'd do, in general terms:

1. First, decide what material you'll use to repair the subfloor. Its thickness is a critical dimension. 3/4" (18mm) tongue-and-groove OSB is a good option, as is a double layer of 1/2" (12mm) OSB.
2. Open the subfloor over the entire damaged area. Cut down the center of joists where possible to avoid the need for repair blocking. Snap chalk lines or use a straightedge carefully to create a straight, parallel, and square-cornered opening (for easier repair). Remove all fasteners and debris.
3. Pull carpenter's lines (drylines) across the gap at appropriate intervals and locations, pulled tight, and snug to the original floor. Any strong string or twine will do. Small nails set at a slight outward angle are a good idea.
4. Sister new two-by lumber to one side of each sagging joist, with their tops the thickness of your new subfloor below the drylines. This is much easier than cutting tapered shims of varying thicknesses, and will result in a flatter floor. This lumber may be higher than the original joists at the outside of the repair opening. We'll address that later. Fasten well with 3" gold construction screws and heavy-duty construction adhesive.
5. Shim up the joists at the edges of the repair opening to the same height as the new sistered lumber. This should be done with strips of uniform thickness. There's nothing to taper or straighten here. The intent, of course, is that the new subfloor comes flush with the old floor.
6. Do any unrelated work in the opening now, such a wiring, duct repair, etc. Clean up dust well with a shop vacuum.
7. Lay in your new subfloor. Orient the sheets so that the strength axis is perpendicular to the joists. Fasten with construction adhesive and screws of adequate length. (If the screws won't pull in flush to the surface without stripping, they're not long enough.) If using two layers, stagger joints so they don't stack. All edges must be supported. Use blocking if needed.
8. Install finish flooring. Be happy on your lovely flat floor.