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Why does Simpson Strong Tie require 2-1/2" nails for the H2.5A connector when the rafter is only 1-1/2 inches thick? The nails into the rafter protrude 1".

The requirement is listed in the table on page 271 of the Simpson Strong Tie 2019-2020 catalogue. I am nailing the H2.5A connector into the double top plate and the rafter.

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  • My best guess is that if the house shifts an inch then the nails will still be in the wood rather than having a complete failure. It's interesting that embed.widencdn.net/svg/ssttoolbox/qmwdmbbor9/… shows nails that do not go all the way through. – MonkeyZeus Dec 22 '20 at 17:46
  • There are columns for use with 1-1/2" nails. Presumably if those columns are blank then it is not an option, but if they are blank then "OK". – manassehkatz-Moving 2 Codidact Dec 22 '20 at 17:51
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    It is telling you the spec fir nailing into the top plate. Common sense is used on the rafter nailing ie don’t use a nail longer than the rafter thickness. – Kris Dec 22 '20 at 17:52
  • I'm not sure "common sense" applies here since there are situations where nail protrusion is required for adequate pullout resistance, such as with asphalt shingles. – isherwood Dec 22 '20 at 17:53
  • @isherwood apples and oranges – Kris Dec 22 '20 at 17:54
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They don't.

The table lists rated uplift loads for particular installation scenarios, presumably with the largest nails that offer practical benefit. It doesn't list installation requirements. See footnote #13 for some clarification. It describes loading for alternative fasteners:

Allowable DF/SP/SPF uplift load for the H .2.5A fastened to a 2x4 truss bottom chord and double top plates using (5) 0.131" x 1-1/2" nails in the top plates and (3) 0.131" x 1-1/2" nails in the lowest three flange holes into the truss bottom chord is 260 lb. (160).

There's also a column toward the right side of the table that mentions 1½" nails. You can see that uplift load is substantially less (540) for short nails than it is for long nails (700).

2½" nails are mentioned for those (rare) cases where you have more depth to nail into. In those cases uplift data is important, so it's listed. It may also reflect the highest load rating achievable with that particular part.

You should use 1½" ("teco") nails into the truss chords (or rafters) and longer nails into the wall plates. This is standard practice. I've done so many times myself under inspection situations.

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  • Ok, but it is a vaulted ceiling with a rafter not a truss, I have read note 13. now and thank you very much. – jrueter Dec 22 '20 at 17:55
  • I'm not sure how that changes anything. :) – isherwood Dec 22 '20 at 17:56
  • For whatever reason (see my comment above), Simpson says the longer nails into the rafter member provides greater resistance to uplift. If your installation says the lower uplift resistance of the shorter nails is sufficient, than you're OK with the shorter nails, as isherwood alluded to. – SteveSh Dec 22 '20 at 18:13
  • No, they don't say that. You've made the assumption that such a nail would be used in a flat 2x4. It wouldn't. It may be for a doubled truss (girder), or for engineered framing where a wider board is used. Those situations are rare, but Simpson opts to provide load data for them anyway. – isherwood Dec 22 '20 at 19:00
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    I'm not disagreeing with your assessment. It has more to do with the way Simpson specifies these products. Since the more common use IMM would be with 2x rafter, I would have thought Simpson would have put that data up in the main table, with the footnote being for the longer nails in 3x or double 2x lumber. Also, while the catalog doesn't say so explicitly, all of the illustrations seem to imply 2x for the rafters. – SteveSh Dec 23 '20 at 1:11

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