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Many of the connections between various members (rafters, collar ties, joists, studs) in the attic of a newly constructed small barn (~1 car garage) have grown over the past year. In short, the nails are not keeping the members together.

How much separation is to be expected? At what separation is fixing them advisable? What method?

Context photos have been removed as they're detracting from the question I'm asking.

  • the picture does not show the extent of the problem ... it shows only one unknown connection ....... but, if they are all like that, then you need to fix now – jsotola May 22 '18 at 17:44
  • 1) I don't believe that's a load-bearing wall (at least at that point as neither member is adequate for such duty), and 2) most modern roofs are self-supporting at the ridge. Please post more photos showing context. – isherwood May 22 '18 at 18:10
  • @jsotola Seems as though NO separation is expected? Hammering back together is likely to re-open so what should be done? Screws? Adding nails at a different entry angle? (I've done some of this - but want to know what I should do - and if it is even needed.) – pathfinder May 22 '18 at 21:53
  • what happened to the picture? – jsotola May 23 '18 at 0:07
  • @jsotola I removed the photos in the question as I'm interested in the general situation - not the specifics and 'discussions' about load-bearing walls. But you made a definitive statement that was helpful - just need to fully understand the details of your comment. i.stack.imgur.com/ooHty.jpg i.stack.imgur.com/lrh1T.jpg i.stack.imgur.com/tb3dJ.jpg – pathfinder May 23 '18 at 14:50
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I don’t see any pictures, but fastening boards together is based on: 1) shear loading, and 2) withdrawal loading.

1) Shear loading is based on a.) thickness of fastener, b.) lumber species, and c.) support of fastener.

Obviously, a.) the larger the fastener and b.) the denser the wood species, the more secure the joint connection. ALSO, c.) if the fastener is cantilevered, it’s shear strength is greatly reduced and the bending capacity of the fastener becomes a factor. Generally we consider the fastener’s shear “fully developed” if it’s not cantilevered more than 1 1/2 times the fastener’s (nail, screw, or bolt) diameter. When it exceeds the 1 1/2 diameter it can reduce the strength of the connection by as much as one-half.

If it exceeds the magic 1 1/2 diameter we then worry about withdrawal.

So, if the fastener has too big of gap or if the fastener is not fully penetrating into the adjacent member, then it is not “fully developed”. However, seldom do we calculate the withdrawal of fasteners.

So, if you’re worried about boards separating and the joint is weakened for shear loading, you need to determine if the connection needs to be at or near “full developed” strength. I doubt it is, especially in residential construction, because residential construction is way over designed.

If this has occurred over a short period of time (less than a year) I’d recommend that it be “monitored “. When we monitor a structural condition we install control points, such as strips of Formica (that won’t shrink or grow) with marks that can be photographed and documented. Keep a journal on a REGULAR basis, like monthly. Document outside temperature, inside temperature, humidity, etc.

  • Based on what I've learned from your answer, others, and my own calculations - fixing it is imperative. Is there a preferred method to bring the members together again? – pathfinder May 26 '18 at 0:11
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    @pathfinder I’d use a clamp. I doubt if you’re moving more than 1/2”, (I don’t see a picture). Check around because some clamps are easier to use than others. When tight together, you could secure them together with wood screws. I’d use a #10 screw about 2 1/2” long, but length should penetrate at least 1”. That will give you about 140 lbs. of withdrawal each, depending on species and grade of wood. Make sure the wood doesn’t split. As an added help, you could over-drill the size of hole in the first board so it pulls the second board in tight. – Lee Sam May 26 '18 at 0:38

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