Hanger Sizing Mistakes
Hangers not only need to have enough load capacity — they also must be sized to fit the framing members they carry. This hanger is too wide for the I-joist, which could allow the joist to move side-to-side and lead to callbacks for a squeaky floor. The bad fit could also cause the hanger to deform, because it’s designed for the joist to bear across the entire width of the seat. Sometimes you can shim the carried member to fit the hanger — but never shim it off-center, because that loads the hanger unevenly.
Sometimes cracks appear where partition walls meet trusses. This could be due to differential shrinkage or settling of framing members, improper drywall installation, or truss uplift. An effective way to allow for vertical movement at this location — while laterally supporting the wall — is to use slotted truss clips. These clips must be correctly installed, with the nail in the center of the slot, or they will restrict truss movement. A few of the common errors I see are nailing too high in the slot, driving the nails in the slot all the way home, and toenailing the truss to the partition.
Most hangers are designed so that the gap between the end of the joist (or truss) and the back of the hanger is no greater than 1/8 inch. An oversized gap — like the one at the back of this truss — places the downward force further from the supporting header, increasing the rotational force on the hanger and reducing its load rating. Luckily, there are ways to deal with oversized gaps. For starters, a number of joist and truss hangers have been tested with gaps of up to 3/8 inch and the reduced loads published. When oversize gaps occur, the designer should compare the design load to the published load and determine whether there is a problem.
It may also be possible to shim or build out the header, though such field repairs should be approved by the building or truss designer. A third option is to use a hanger that has a deep seat and added nailing capacity, and can handle gaps up to 1/2 inch.
Poorly Installed Top-Flange Hangers
Because of their flexibility, top-flange hangers are often installed with the sides splayed open. This lifts the seat, which puts bumps in the floor and creates the potential for squeaks. A similar problem occurs when the bottom of a top-flange hanger is not tight against the header. Not only does this put a lump in the floor — it also reduces load capacity. When the framers dropped the I-joist into this hanger, they should have pushed it back against the header.
Improper Attachment of Top-Flange Hangers
Top-flange hangers frequently hang from sills or plates attached to foundations and steel I-beams. Keep in mind that the edge of the nailer should be flush to the edge of the supporting concrete or beam, or overhang it by no more than 1/4 inch. If the plate overhangs too far, it may split. It’s also important to select a hanger rated for use with a wood nailer and to install it with the right fastener. The installation instructions for the hardware include a table identifying the suitable nails, depending on whether the nailer is a single or double 2-by or a 4-by. Here, the hanger on the foundation wall is correctly installed, but there are several problems with the hanger on the I-beam. The nailer projects too far beyond the beam, and the empty holes in the flange indicate that an inappropriate hanger was used. There should be 16-penny nails in those holes.
Penetrations Through Wall Plates
Well-intentioned trade contractors usually try to repair top plates at mechanical and plumbing penetrations, but they don’t always do it correctly. Under IRC section R602.6.1, when more than 50 percent of the width of a top plate is drilled or notched out, the plate must be reinforced on both sides with a 16-gauge metal strap attached with eight 16-penny nails on both sides of the hole or notch. IRC section P2603.2.1 specifies that any pipes that aren’t cast iron or steel within 1 1/2 inches of the edge of the framing must be protected by a 16-gauge steel plate that extends 2 inches past the top and bottom plates. The small nail stoppers on this wall meet neither requirement and should be replaced with a protecting shield plate like the one shown.
Unique and unexpected framing connections always seem to come up at just the wrong moment. While it may be tempting to save time and trouble by modifying a connector that is already on site, don’t do it. Bending can cause fractures, changes the geometry of the connector, and may reposition fasteners into weaker areas of the lumber. The side flange of the hanger supporting this glulam beam was hammered flat, and someone cut this hurricane tie in half to make it fit a double truss. Both pieces of hardware will have to be replaced, because no manufacturer will warrant or guarantee the performance of modified connectors unless they’re specifically engineered for field sloping or skewing.
Jim Mattison is a senior territory representative for Simpson Strong-Tie in the Northwest and Alaska.