Deck Ledger Connection Checker

Five things, reported line by line rather than as one verdict. What the ledger lands on: whether the band joist is conforming and bears fully on the structure, whether the ledger is on veneer, whether a beam bears on it, the ledger member itself, the fastener material and the flashing. Vertical support: the on-centre fastener spacing required at the joist span you enter, for the fastener and sheathing thickness you select, compared with the spacing as built. Placement: the number of rows, the spacing between rows, and the distances from the top edge, the bottom edge and the ends. Lag screw preparation, where lag screws are selected: the clearance hole through the ledger, the smaller pilot hole into the band joist, whether the tip fully extends past the inside face, and whether the screws are full-body diameter. And the lateral connection, which is a separate requirement the fastener schedule does not satisfy.

Because three conditions void the fastener table entirely, and a spacing number produced in spite of them would be worse than no number at all. A ledger may not be supported on stone or masonry veneer. The band joist has to be 2-inch nominal solid-sawn lumber or an approved engineered rim board and has to bear fully on the primary structure, which a cantilevered floor or an overhang does not. And the ledger may not carry a concentrated load from a beam or girder, because the table is derived for the uniformly distributed load of joists bearing along its length. Where any of those is true the tool withholds the lookup and says which condition failed, because the connection has stopped being a table lookup and become a design question.

Because the spacing is a function of three inputs at once: the span of the joists bearing on the ledger, whether the fastener is a half-inch lag screw or a half-inch through bolt, and the thickness of the sheathing between the ledger and the band joist. For half-inch lag screws the tabulated spacing runs from 30 inches on centre at a joist span of 6 feet or less down to 10 inches at a 16-to-18-foot span. Through bolts carry more and are tabulated further apart, and they are tabulated separately for sheathing up to half an inch and sheathing up to one inch. A single remembered number is correct for exactly one row of the table. The tool takes the span and derives the requirement rather than asking you which figure you had in mind.

They resist different forces, and this is the distinction the tool exists to make visible. The fastener schedule resists the deck's vertical load — everything on the deck pressing down through the joists into the ledger and into the house framing. The lateral connection resists the deck moving away from the building. The code gives two paths: devices rated at not less than 1,500 pounds at not fewer than two locations per deck, within 24 inches of each end, or devices rated at not less than 750 pounds at not fewer than four locations. These are rated hardware items with their own load path back into the floor framing, not additional lag screws. When the tool finds a fully compliant fastener schedule and no lateral devices at all, it says so by name, because that combination is a compliant-looking ledger that is not a compliant ledger.

Because the code asks for two, and they do opposite jobs. The hole through the ledger and through any sheathing is the full half inch, so the shank passes through freely and the head can draw the ledger tight against the wall. The hole continuing into the band joist is between 5/16 and 3/8 of an inch, so the threads have wood to cut into and can develop withdrawal resistance. Drilling one half-inch hole straight through is faster and removes most of what holds the deck on, and it is invisible once the screw is in. The tool asks for both diameters as separate numbers for the same reason it asks for the well depth in two parts elsewhere: one field called 'hole size' invites a single answer to a two-part question.

Because the table does. The tabulated on-centre spacings run to a 16-foot-1-inch to 18-foot joist span and then end. Beyond that the prescriptive path has no answer, and extrapolating the trend would produce a plausible number with nothing behind it. The tool reports that the span is beyond the tabulated range and withholds the lookup, which is the same behaviour it applies to the three disqualifying conditions. A deck with joists spanning more than 18 feet onto a ledger is an engineered connection.

No. It is a preparation aid that performs lookups and arithmetic on figures you supply and answers you give. It asserts no product specifications and makes no finding about a specific deck. The thresholds are those of the model residential code for deck ledger connections to a band joist; the edition your jurisdiction has adopted is the one that governs, and this section has been renumbered between editions as well as amended at state and local level, so the section number you find in an older document may describe the same requirement at a different address. The table also carries load assumptions of its own. A blank measurement is reported as not measured and excluded rather than filled with an assumption. The determination belongs to the building official, and the scope belongs to the permit.