Sistering joists that have wires in them
Anna Massi
5 years ago
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Quick question about sistering joists
Comments (4)coast2, I agree with dooer. Rule of thumb and code is usually up to 2'. Now you are mentioning an overall cantilever of 48" - thats questionable. I'd check with your local building department as to their recomendations. All the best, The PorchGuy Here is a link that might be useful: My Album...See Moresistering floor joists
Comments (16)The longer the better. You are making a composite beam with the wood and the metal strap. The holes for the screws in the metal need to be tightly matched to the screw shank diameter. A slight interference fit (a few thousandths of an inch) is actually better than a clearance fit. For the joist to sag the bottom surface must get longer as it flexes to a curve. The steel and screws prevents that from happening, but only if the slightest movement is transferred to the steel immediately. It is more effective than a plain flitch beam with metal attached to the side of the joist. Flitch beams have the same issue with hole clearance on the fasteners, and add buckling of the steel away from the joist to the issue. One of the reasons a classic flitch beam sandwiches the metal between two joists. The fasteners than go all the way though both joists and the steel between them, limiting chances of buckling even with relatively thin metal (and the double joist immediately adds more stiffness). The flitch can be a PITA for wiring and plumbing though. It is much harder to drill through the typically hardened steel plate often used for the metal. This post was edited by brickeyee on Sat, Apr 13, 13 at 14:39...See Moresister a joist with steel?
Comments (9)Flitch plates are normally used between wood members (and through bolted repeatedly) to provide the plate with buckling resistance. The metal is normally relatively thin compared to its height. By trapping it between wood members you prevent buckling, but it needs enough fasteners to not exceed the crush rating of the wood in two planes. The structural load is vertical (parallel to the height of the beam) and the buckling load horizontal (perpendicular to the face of the beam). You could use thicker metal but it would be far more effective to either use u-channel or angle iron across the damaged area. I would use either U or angle on both sides with though fasteners. The leg of the angle perpendicular to the side of the beam acts to prevent buckling and the metal on each side distributes the load across the face of the beam and prevents crushing under the fasteners....See MoreSistering joist questions
Comments (3)Trimming the sister shorter does not make much difference since sag is not a bearing area issue. The problem with any type of jacking is that the old joist may have a set that will not go away very quickly. If you want to try and straighten the old joist before sistering watch what is happening very carefully as you start to lift the middle. Some joist will give enough, but many will not and the end(s) can actually be lifted off their bearing location. Raising very gradually (1/8 inch per week type numbers) can give the old wood some time to move back into a straight line. Glue is not normally needed, and in most cases is assigned a zero strength since application is so variable. All you need is a slightly thicker glue line to render it useless, and correct glue line thickness is very thin (thousandths of an inch over the entire glue area). Clamping is required to even get close to a correct glue line. 16d nails are more than adequate. While bolts and lag screws may appear better if you use fewer of them tan you would nails you can easily exceed the compression limits of the wood. There are nailing rules for new work that can serve as a starting point, but older lumber may have been ungraded or just over spanned, making a more frequent nailing schedule needed....See Moreksc36
5 years agolast modified: 5 years agoAnna Massi
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