Walking a deck rough-in: 2x10 joists in LUS28 hangers, the hangers are nailed with 1-1/2 inch galvanized roofing nails in the face holes and the diagonal joist holes are empty, and the joists are sitting about 3/4 inch above the hanger seat because the hanger was nailed up first.

No, this is not safe and does not meet code.

Key Issues:

1. Hanger Seat Gap: The 3/4" gap between the joist and the hanger seat is a critical failure. The joist must bear fully on the seat per IRC R577.3 and the hanger manufacturer's installation instructions (e.g., Simpson Strong-Tie). This gap means the joist is suspended by the face nails only, which are not designed for this load path.

1. Incorrect Fasteners: 1-1/2" roofing nails are wrong. IRC R577.3 requires #10 (0.148" shank) x 1-1/2" (min) common nails or the specific fasteners listed for the hanger. Roofing nails often have different shank diameters and head types, compromising the connection.

1. Missing Diagonal Nailing: The empty diagonal holes are required by IRC R577.3 and the hanger's listing. These nails resist uplift and lateral forces.

1. Installation Order: Nailing the hanger first, then placing the joist, led to the gap. Hangers must be installed with the joist properly seated.

Immediate Action Required: Remove the joists, correct the hanger placement (or replace if damaged), install the correct fasteners in all holes, and ensure full bearing on the seat. Do not load the deck until corrected. This requires a permit and inspection in most jurisdictions.

No, it is not solid. This is a critical structural failure requiring immediate correction.

Three code violations (IRC R507 / Manufacturer Instructions):

1. Wrong Fasteners: LUS28 hangers require 10d common (3") or 16d common (3-1/2") nails for face nailing into the ledger/beam. 1-1/2" roofing nails have ~1/3 the shear capacity and zero withdrawal resistance in this application. They will pull through the hanger flange under load.
2. Missing Joist Nails: The diagonal/obround holes in the joist must be filled (typically 10d x 1-1/2" joist hanger nails). Empty holes = zero download/uplift transfer into the joist. The joist is sitting loose in the stirrup.
3. Improper Installation Sequence / Gap: Hangers must be installed after the joist is cut to length and seated. A 3/4" gap at the seat eliminates bearing capacity. The hanger side flanges are now acting as cantilevered brackets, a condition they are not rated for.

Required Fix:

1. Remove all roofing nails.
2. Remove hangers.
3. Cut joists to bear fully on hanger seats (max 1/16" gap per mfr).
4. Install hangers with correct nails: Face: (4) 10d/16d common into ledger. Joist: (6) 10d x 1-1/2" hanger nails into diagonal holes.

Do not cover this. It will fail under design load (people/snow). Owner's "feel" is irrelevant; this lacks the engineered load path.