Floor Joist Sister

Inspecting the crawl space I cam across some floor joist repairs.
I noticed that the repairs were made to 7 termite damaged joists by sistering 2x8 16’ boards to the existing joist.
However, I notice that the repairs were made by using 2 4" screws about 12 - 16 " apart, I thought 3 screws would have been better and there were no lag bolts used.
What was concerning to me is the screws were screwed in from the rotted wood to the new board, I would have thought the screws should be good wood to bad.
I wrote my report recommend that an engineer check this out. I’m curious about the repair, I haven’t run into this before and I’m asking my fellow members for their input on this type of repair.

In my experience, sistering a joist to repair a damaged one calls for copious amounts of 16-penny nails driven into healthy wood to effect a proper repair.

You were right to refer to a structural engineer.

Thanks William for your reply.
I was told that a type of “C” clamp are also good for added support.
Have you seen this type of clamp during your Inspection or heard of
Thus being used.

Can’t say I have. If it’s the kind of C-clamp I am thinking about - like you use in a workshop - then no, I can’t see that providing the kind of solid, slip-proof attachment one would desire.

When I was building homes, I seem to recall the standard for sistering being that the sister would extend at least 4 feet either direction from the sound portion of the compromised member with 2 or more nails (depending on the width of the member - essentially one for every 2 inches of width) placed every six inches along the length of the sister.

Machine bolts (not lag bolts) could also be used, though not as many would be required.

Someone with a better memory may be able to cite the proper standards. Essentially, there should be enough fasteners that the sister will fail before the fasteners do.

Thanks again William for your input - you memory serves you well…