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Hurricane ties are the metal connectors that hold rafters and trusses down on their walls when wind lifts the roof. IRC R802.11.1 requires each truss to be attached for the uplift on its design drawings and each rafter for the uplift in Table R802.11; only at 200 lb or less with framing 24 in on centre or closer may plain toe-nailing do the job. The Hurricane Tie Calculator counts the rafters or trusses (length ÷ spacing + 1), puts a tie at every end on each bearing wall, checks your uplift against the allowable uplift of the tie from ICC-ES report ESR-2613 Table 1 — H3 400 lb, H1 470 lb, H1A 545 lb, H2.5A 700 lb, H7Z 830 lb, H10A 1,040 lb for Douglas fir-larch or southern pine — and counts the listed nails. A 40 ft roof with trusses at 24 in has 21 trusses and 42 ends; at 450 lb uplift that is 42 H2.5A ties and 420 nails.
IRC R802.11.1 requires every truss to be attached to its wall for the uplift on its design drawings and every rafter for the uplift in Table R802.11 or from engineering; where the uplift is 200 lb or less and the framing is 24 in on centre or closer, the toe-nailing in Table R602.3(1) is allowed. Allowable loads below are from ICC-ES evaluation report ESR-2613 Table 1 for Douglas fir-larch or southern pine (specific gravity 0.50 or more), wind or seismic load duration.
| Model | Uplift | Lateral F1 / F2 | Nails to rafter | Nails to plates |
|---|---|---|---|---|
| H2.5A | 700 lb | 110 lb / 110 lb | 5 | 5 |
| H1 | 470 lb | 510 lb / 190 lb | 6 | 4 |
| H1A | 545 lb | 420 lb / 265 lb | 4 | 4 |
| H3 | 400 lb | 210 lb / 170 lb | 4 | 4 |
| H7Z | 830 lb | 410 lb / — | 4 | 2 + 8 to stud |
| H10A | 1,040 lb | 565 lb / 285 lb | 9 | 9 |
The IRC (R802.11.1) requires every rafter and truss to be connected to the wall for its uplift force: trusses for the uplift on their design drawings, rafters for the uplift in Table R802.11 or from engineering. Only where the uplift is 200 lb or less and the framing is at most 24 in on centre may plain toe-nailing from Table R602.3(1) be used. In practice most wind areas need a metal connector at every rafter or truss end.
One per rafter or truss end on each bearing wall, more where one tie is not strong enough. A 40 ft roof with trusses at 24 in has 21 trusses and 42 ends; at 450 lb uplift one H2.5A (700 lb) per end is enough, so 42 ties and 420 nails.
700 lb of uplift with five 0.131 × 2 1/2 in nails into the rafter and five into the plates, per ICC-ES report ESR-2613 Table 1, for Douglas fir-larch or southern pine (specific gravity 0.50 or more) under wind or seismic load. Its lateral capacity is only 110 lb each way, so it is not a substitute for blocking.
Match the allowable uplift to the uplift you have to resist: from ESR-2613 Table 1, H3 400 lb, H1 470 lb, H1A 545 lb, H2.5A 700 lb, H7Z 830 lb and H10A 1,040 lb. If one tie is not enough, pick a stronger model rather than doubling up — two ties on one rafter need a rafter at least 2 1/2 in thick when they sit on both sides.
The nails the evaluation report lists — for the H2.5A, 0.131 × 2 1/2 in (8d common); for the H1A and H1 rafter leg, 0.131 × 1 1/2 in; for the H10A, 0.148 × 1 1/2 in. Use every hole the table calls for; roofing nails and drywall screws are not substitutes.
Sizing the joists that sit on the same wall? The ceiling joist span chart gives the IRC spans.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.