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I live in a 1950's cape house with a finished attic. The rafters are nominally 2x6. I want to refinish the attic with better insulation and called in a structural engineer to make sure the roof is up to holding the additional weight of insulation and snow load. The verdict was it should be good with some reinforcement. The engineer advised me to a) reinforce each collar tie to rafter connection with a 5/8 in bolt and b) nail 2x's across the rafters along the top plates in the attic and attach the bottoms of the rafters to the 2x's with twist straps. The idea being to have the straps tie the rafters to the joists and do more to keep them from sliding out and my roof pancaking.

I toyed around with a 12 in simpson strong-tie twist strap to see how it fits and I should be able to make it work if I run 2x6's along the top plate. What's giving me pause is that the rafters are toe-nailed to the top plate and the nail heads are are right where the strap would go. Strap placement Nails in the way of strap

Is it safe to grind the nail heads flush with the surface? Is it safe to drive more nails that close to the end of a 70 year old what I think is douglas fir rafter? I would pre-drill and only nail through the top 4 holes on the strap but I'm cautious because I've worked with similar lumber elsewhere in the house and it's petrified. Am I misunderstanding what the structural engineer suggested and have this backwards somehow?

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  • You paid your money - ask the engineer for clarification if it's not clear...
    – Ecnerwal
    May 5, 2020 at 1:45
  • @Ecnerwal: Money payed was for a structural assessment visit. Testing, deeper analysis, drawings and parts specifics would be an additional service. That he recommended this at all was a bonus, as I understand it, so when I asked for follow-up he was reluctant to give more specifics for scope and liability reasons and I don't want to push him.
    – user116817
    May 5, 2020 at 15:02

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Just tap the toenails in deeper. Use a finer tipped chisel if you need to. Then attach it as the engineer has specified.

Even if the wood is rather old, the direction of the force that the nails and bolts are acting in shouldn't rip it apart. It'd be noticable if it was dangerous from your photo and that's not the case.

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  • Thanks for the response. Is tapping them in just less trouble than grinding the part of the nail head that's sticking out or does grinding the head compromise the nail?
    – user116817
    May 5, 2020 at 14:51
  • I agree that grinding them would compromise the nail. You want that to be there and entirely intact.
    – represton
    May 5, 2020 at 14:55
  • Is it best not to nail through the bottom row of holes, even with pre-drilling? They're only a bit over 1/2 in from the end of the rafter.
    – user116817
    May 6, 2020 at 14:40
  • Do you mean have the nails on the bottom row penetrate to the other side of the rafter?
    – represton
    May 6, 2020 at 14:44
  • In the 1st photo, you can see there are 4 holes along top edge of the strap and 3 holes along the bottom. I was going to only use the top 4 holes. 4 nails seems sufficient. The 3 bottom holes are very close to the edge that sits on the top plate and are in line with the top holes along the grain of the rafter. I am concerned that if I use the bottom row of holes, cracks will form and the end of the rafter will degrade. Just being very cautious in making sure I don't make things worse. Am I wrong?
    – user116817
    May 6, 2020 at 14:51

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