![]() ![]() In this case the rafter as a whole is actually stronger than it would have been because the splice is more than adequate and the plywood adds to the strength. Pictured at left is a 2圆 rafter spliced together using 3/4” plywood. Also contractors could not be sure their workers were experienced enough to do this properly and so opted for engineered wood for liability reasons. Plywood can be used to accomplish the same thing and for many years many carpenters made their own job built trusses using plywood as the gusset This practice fell by the wayside mostly because manufactured trusses came down in price. It is stamped into the wood at the factory with a hydrolic press. A gang-nail is basically a thin piece of metal stamped out so that many metal tangs stick out into the wood about a 1/2” or so. The truss companies use a “gang-nail” to splice wood together (pictured at left). ![]() The most common “mistakes” in this method would be not nailing the sisters together good enough, inadequate bearing on one side or another, If the new sister bears on wood at least 1.5” on each end then you're good to go. Essentially sliding a whole member beside it and nail the heck out of it from both sides with a lot of nails). The most common way joists are repaired is to “sister” it up. Most common causes is lack of proper nailing technique and splicing to compromised wood. Whatever the reason substandard repairs can be structurally deficient. Supervisors are often reluctant to review their employees work. Crawlspaces can be tight and uncomfortable to work in so the temptation for shortcuts and substandard workmanship is common. Comments to this blog is encouraged.Īt left is a diagram of some inappropriate repair techniques. Every project is different and has their own particular load bearing criteria which may necessitate different methods, additional support or even engineering analysis. This discussion is not intended to give credence to any particular splicing project and can not substitute for proper engineering analysis but is only intended to help guide carpenters as to the proper concepts and best practices for proper splicing procedures. The connection method has to be so good that the separate units will act as one unless a whole unit is substituted or “sistered up”. Whatever the reason the secret to a good splice is the connection method and good workmanship. Sometime we just need a longer piece of wood (like a hip king rafter). Of course we're talking about splicing a joist or rafter as part of a repair technique for a rotted, termite damaged or over spanned joist. The fact is that there are many things carpenters do that are allowed because we all know they work. Headers, jacks, sills, beams, girders rafters, are all spliced together in one way or another. It's one of the things carpenters do best but still there are those who say that this is the purvue of an engineer and no one else. We'll begin our discussion by reminding everyone that carpenters have been splicing wood together for thousands of years. ![]()
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