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Simpson Strong-Tie has a catalog entitled “The Well-Connected Structure”. Call at 800-999-5099. Visit at http://www.strongtie.com.
Page 61 of that catalog contains the different “twist straps” used. It is said that these straps are used for hurricane.
I was watching one of those shows about disasters, this one being about hurricanes, and they interviewed a guy who said…”and those straps snapped like rubber bands”…
In that situation, the winds were estimated at 180mph.
I have just used the LTS-20 twist straps for this remodel of a 1920 Colonial Craftsman home in Cleveland. I have used them often. I have used them on all rafters, at several points on the rafter.
When I heard that guy, I got worried because I thought that I had done enough. So, I thought about it, talked to Simpson engineers, and came up with some thoughts.
The weakness in the LTS type straps seem to be at the twist, after having attained full restriction of movement from the length of the tie. Because of this, I believe, it is important that each rafter is tied with a tie which fits around the top and both sides of the rafter, down the plates, and to both sides of the studs. The H-15 exemplifies this for a rafter. However, this type should be available in a longer version for trusses.
I do not believe in the idea of holding back the upload. Rather, I believe that movement should not be allowed to begin the weakening process of the bracket. Also, trusses, as I understand them, offer very little resistance to twisting. And that is what I believe is occurring with wind loads.
If I had trusses, I would glue and nail good sized 3/4″ ply over everyone of those connection plates in each truss. Then, I would be darn sure to put in blocking between each truss, at each part of the truss that is an individual piece. The idea being, to restrict movement.
Imagine that you have made a scaled down version of your house, and you are standing over it, take your hand and twist the house. It is rigidly connected to the foundation, so where does it move when you twist?
Address those points.
Any house should be made so that it can be made to be picked up and rolled down the street like dice on a crap table, then picked up with a crane and put back on the foundation.
Hope this helps.
Replies
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It would seem to me then that those of us who have never stopped cutting our own rafters are in the 'cat bird seat'; by the time you finish rebuilding your trusses I could have the roof framed right, the first time, although I'd be a titch leery about having you roll it down the street like a dice. . . just being cautious ya know.
never catty
Patrick
*I would strongly recommend using some sort of tie down anchor, rather than just toe nails. Wind design is one of the most overlooked area of modern house design. Properly nailed plywood on trusses makes a nice rigid structure, which can blow off in one piece like a big airplane wing. Watch one of those shows on the Discovery channel anout hurricanes - You'll see the roofs of houses flying off like a cap blowing off your head. Also, make sure the rest of your structure is tied together. Walls are often just nailed to the subfloor, and aren't tied down well. That baloney about putting plywood over the truss plates is ridiculous. I can't imagine that it would do a bit of good, and it would be very expensive. Best of luck with your house.........
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Great rebuttal patrick.... i agree...
eric
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I am going to support Ron's comments here.
I will retract, for now, my remarks about plywood over the perforated metal connectors, based upon my recollection of those Discovery Channel shows that the trusses did remain intact.
Yes, I have seen the roofs come up like a hat. But, more than that, I have seen what appears to me to be a peeling of the roof: whereas the wind picks up a corner and from that corner over the roof is lifted.
These are torsional forces which, I believe, are not compensated for in the truss type roof.
One thought is whether a full-length 2x4 could be set within the truss, and over the walls' top plates, so that such 2x4 could be through-bolts to the plates.
My aim is to make the roof more monolithic with the house. I hope to make a better connection with wood than seems possible to achieve with straps. I think the answer may lie in the old balloon type framing, where a simple 1x4 is used to hold up second floor joists.
Is my thinking clear? Am I focused, pointed in the right direction?
Hope this helps.
*RE: OTHER CONNECTORSRather than wood, the member could use tubular steel so that splices might be made. I guess a 2x2 is a good size for discussion herein...the Simpson Strong-Tie HD-2A is used at the foundation and to connect the floors, and then, is used at the top plate where a bolt connects the 2x2.Hope this helps.
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It seems to be common practice in my neck of the woods to affix trusses to the wall top plates with 16d nails toenailed. In my case, my carpenters used 3 nails per truss end. There are many nails not fully seated, some are barely hanging on to anything and several of the trusses are not resting on the plate at all, but hanging a heavy 1/8" above the plate. The engineering side of me says that there should be more holding my roof down than what we have. I live in St Louis, and we get occasional 70mph winds, but not much of a snow load. Comments? If the nails are sufficient thats great, but I can fix things now before we proceed further if it makes sense.
Thanks in advance.
*In most jurisdictions in the west, Simpsons H-anchors of some kind are becoming commonplace and often required. The particular anchor depends on the specific application. See their website at strongtie.com
*We're undergoing some major revisions in the building code here in Wisconsin and one of the new provisions is the requirement for rafter ties in addition to the standard use of spikes to hold trusses and rafters in place.
*Simpson Strong-Tie has a catalog entitled "The Well-Connected Structure". Call at 800-999-5099. Visit at http://www.strongtie.com.Page 61 of that catalog contains the different "twist straps" used. It is said that these straps are used for hurricane.I was watching one of those shows about disasters, this one being about hurricanes, and they interviewed a guy who said..."and those straps snapped like rubber bands"...In that situation, the winds were estimated at 180mph.I have just used the LTS-20 twist straps for this remodel of a 1920 Colonial Craftsman home in Cleveland. I have used them often. I have used them on all rafters, at several points on the rafter.When I heard that guy, I got worried because I thought that I had done enough. So, I thought about it, talked to Simpson engineers, and came up with some thoughts.The weakness in the LTS type straps seem to be at the twist, after having attained full restriction of movement from the length of the tie. Because of this, I believe, it is important that each rafter is tied with a tie which fits around the top and both sides of the rafter, down the plates, and to both sides of the studs. The H-15 exemplifies this for a rafter. However, this type should be available in a longer version for trusses.I do not believe in the idea of holding back the upload. Rather, I believe that movement should not be allowed to begin the weakening process of the bracket. Also, trusses, as I understand them, offer very little resistance to twisting. And that is what I believe is occurring with wind loads.If I had trusses, I would glue and nail good sized 3/4" ply over everyone of those connection plates in each truss. Then, I would be darn sure to put in blocking between each truss, at each part of the truss that is an individual piece. The idea being, to restrict movement.Imagine that you have made a scaled down version of your house, and you are standing over it, take your hand and twist the house. It is rigidly connected to the foundation, so where does it move when you twist? Address those points.Any house should be made so that it can be made to be picked up and rolled down the street like dice on a crap table, then picked up with a crane and put back on the foundation.Hope this helps.
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And you would have also created more usable space.
Hope this helps.
Grrr...