Ledger Bolt Calculator

Through-bolts are stronger (380 lb vs 250 lb allowable per fastener — 50% higher) and significantly less likely to pull out under cyclic load (the failure mode that drops decks). They go all the way through ledger + house rim joist + a washer + nut on the inside. Trade-off: you need backside access to the rim joist (unfinished basement or crawl space). If your basement is finished or the rim is hidden behind drywall, through-bolts are impractical without major demo. In that case, ½″ lags or Simpson SDS structural screws are the right pick.

IRC R507.9.1.3 prescribes ½″ × 5½″ lag screws with washer + lock washer (the historic standard, 250 lb allowable per fastener). IRC R507.9.1.3.1 added an alternate fastener path in 2018 that allows Simpson SDS structural screws (Simpson's ICC-ESR rating gives them an engineered allowable load). The advantages of Simpson SDS: no predrill required (drives in faster), smaller hole (less rim splitting), heat-treated steel (higher per-fastener strength), and ICC-ES certified for IRC compliance. The historical advantage of lags is just availability and price ($2.20 vs $2.65 per fastener). For new construction we recommend Simpson SDS25500 — faster install + IRC-approved + less splitting.

Depends on ledger depth + joist span. IRC R507.9.1.3 implies single-row for 2×6 and 2×8 ledgers (insufficient height for 2 rows + edge distance compliance). 2×10 and 2×12 ledgers with joist span 12 ft+ require 2 rows of staggered fasteners — the row spacing is 1-5/8″ between rows, and bolts must alternate between rows (no two bolts in a vertical line). Two rows roughly DOUBLE the connection capacity and dramatically reduce the rotation-induced pullout failure mode that drops single-row ledgers.

Yes — required per IRC R703.4. A metal Z-flashing tucked under the wall siding above the ledger and lapped over the top edge of the ledger directs any water that runs down the wall AROUND the ledger instead of behind it. Skipping this is the #1 cause of rotting house framing behind deck ledgers — and it happens silently inside the wall cavity. Cost: about $4.20 per LF for 24-gauge stainless or galvanized Z-flashing. For a 16-ft ledger = $68. Cheapest insurance you can buy on a deck.

No — never directly. Brick veneer is not structural; it's hung from the house framing with metal ties, and it can't support deck loads. Three options: (1) remove brick in the ledger zone + lag through the sheathing into the rim joist (most common — but requires careful brick replacement after), (2) full freestanding deck design (no ledger, posts at house side), or (3) engineered ledger attachment with long bolts through the brick + structural rim + interior nut. Option 2 is by far the easiest and what we recommend — the Ground-Level Deck Calculator + Floating Deck Calculator both handle freestanding designs.

Most engineered rim joists can accept a standard ledger attachment, but with two caveats: (1) The fastener must penetrate solid material — either the LVL itself or a solid wood block installed inside an I-joist web (the web alone won't hold). (2) The I-joist manufacturer's installation guide governs — Boise Cascade, Weyerhaeuser, LP all publish ESR documents specifying acceptable fasteners. Always involve a structural engineer for engineered framing. Standard 2×10 dimensional rim is much simpler.

Significantly. At 12-ft joist span, the IRC table goes from 15″ OC (no snow) to 12″ OC (30+ psf snow) — that's 25% more fasteners. At 18-ft span, 10″ OC drops to 8″ OC — also 25% more. The reason: snow adds to the joist tributary load that ends up pulling the ledger away from the house. North-snow zones (Minnesota, Maine, upstate NY) commonly run 35-50 psf snow. Always design for your actual ASCE 7 snow PSF, not the IRC minimum.

For typical decks (residential, IRC-compliant, 50 psf design load), yes — the calculator IS the IRC R507.9.1.3 table. For non-typical decks (over 100 sqft per IRC R507.1 in some jurisdictions; hot tub on the deck; engineered I-joist house framing; brick veneer attachment; log home; seismic zones with lateral load requirements; multi-story decks), you need a stamped engineer letter regardless. Cost: $400-1,500 for the letter, $2,500-5,000 for full engineering. Always check with your local building department first — many jurisdictions accept the IRC table for typical decks but require an engineer for anything outside.

Rotation-induced pullout. As the deck takes load, the joists try to rotate at the ledger connection (top of joist pushes against the wall, bottom pulls away). Single-row fasteners only resist this rotation at one point — the bottom row of fasteners gets the highest pullout force, and a tight bolt spacing AT THE BOTTOM is what prevents collapse. Two-row attachment with 1-5/8″ row spacing creates a couple-resisting connection that handles rotation far better than single-row. This is why 2×10+ ledgers with 12 ft+ joist spans require two rows under IRC R507.9.1.3.