How to use this calculator
- Enter tributary width. Use the deck width carried by the ledger, often half the joist span for a simple ledger-to-beam deck bay.
- Enter area loads. Use live and dead loads from your design basis, not just a generic default.
- Enter fastener data. Use the allowable per fastener and the number of fasteners sharing each spacing interval.
- Set spacing cap and candidate. Enter any maximum spacing cap you need to enforce and the spacing you want to check.
- Review utilization. Use the governing spacing and utilization to decide whether the layout needs tighter spacing or engineering review.
How it works
This deck ledger fastener spacing calculator starts with the load carried by the ledger. Area load is multiplied by the tributary deck width:
w = (q_L + q_D) * b_t
The entered demand factor is then applied:
w_d = w * K_d
The capacity available at one repeated spacing interval is:
F_interval = n * F_allow
Maximum spacing from the entered fastener allowable is:
s_F = F_interval / w_d
The reported governing spacing is the smaller of that spacing and the entered maximum spacing cap:
s_max = min(s_F, s_cap)
At the checked spacing, utilization is the checked interval load divided by the entered interval capacity.
Worked example
Verified against the live calculator
A deck ledger carrying 6 ft tributary width at
40 psf live load plus 10 psf dead load sees about
300 lb/ft of ledger line load. With two entered
300 lbf fasteners per spacing interval, the capacity-based
spacing is about 24 in. A 16 in checked spacing
uses about two-thirds of that entered fastener capacity before any other
code or manufacturer limit.
Frequently asked questions
Is this a deck ledger code table?
No. This is an explicit-input load and spacing screen. It does not replace adopted IRC/AWC deck ledger tables, product installation instructions, engineer review or local inspection.
How does tributary deck width affect ledger fastener spacing?
The ledger line load is the deck area load multiplied by the tributary deck width carried by the ledger. A larger tributary width increases line load and reduces allowable fastener spacing for the same entered fastener allowable.
What should I enter for allowable per fastener?
Use the allowable load for the actual screw, bolt or connector from the relevant code, manufacturer data or engineered design, including substrate, edge distance, spacing, corrosion and load direction.
What does fasteners per interval mean?
It is the count of fasteners assumed to share load at each repeated spacing location, such as two staggered rows at the same spacing interval.
Does this check lateral tension or uplift connectors?
No. It screens load per repeated ledger fastener interval only. Lateral-load connectors, uplift, withdrawal, masonry anchorage, flashing, decay and inspection requirements are separate checks.
Method & assumptions
- Uniform deck area load and uniform tributary width to the ledger.
- Fasteners at each spacing interval are assumed to share the checked load direction equally.
- The entered allowable per fastener and spacing cap are user inputs, not embedded code or product-table values.
- Does not check prescriptive ledger tables, lateral-load connector rules, withdrawal, uplift, bolt/screw group effects, edge distance, stagger patterns, rim/band joist capacity, sheathing between members, flashing, decay, corrosion, masonry/concrete anchorage, guards, stairs, hot tubs, concentrated loads, inspection or permit approval.
- Use deck joist span, deck beam span, deck board takeoff and deck footing concrete for adjacent deck planning checks.