What are Your Options to Address Member-to-Member Gaps?

A recent phone call has prompted me to address the issue of fixing gaps. There are some misunderstandings about what qualifies as a member-to-member gap, and the options to fix them are not always clear either.

ANSI/TPI 1 recommends that members in a truss to touch each other when possible. The tight contact helps transfer loads from one member to another without depending on the connector plate to translate the load through the truss and ultimately to the bearing. Sometimes, member-to-member gaps happen. Sometimes, it’s a mis-cut. Sometimes, it’s the pressing operations. Often, it is the degree of variation of web and chord members, because wood is a natural product and can vary due to properties and the manufacturing process.

The standard allows for repairs per 3.7.6.3 Correction Procedure by inserting a metal shim. The standard states:

“Corrections procedures for joints with gaps exceeding these tolerances shall require shimming, unless otherwise specified by the Truss Designer. Shims shall be of galvanized metal, or alternatives approved by a truss designer, to obtain firm bearing between members…”

Using a Metal Shim vs. Rebuilding the Component

The shim has specific requirements, as follows:

1. Must be metal
2. Must be coated to reduce rust potential.
3. Must be secured in place with a specific nail size or an approved fastener.
4. Must be at least ¾” wide.
5. Must have a folding tab that allows the shim to be secured or an approved alternate method of securing the shim as specified by the truss designer.

By now, if you’re a normal, competent truss manufacturer you might be asking, “why on earth would I not just pull the truss apart and fix the problem?” Well, this aspect might need some discussion.

Situations where pulling the truss apart is not reasonable include these examples:

1. Removing connectors and replacing a connector may not be possible due to ANSI/TPI 1 Section 3.9.3, because removing the connector requires a larger connector to make up for the 50% reduction requiring a larger connector. A good example of this might be a floor truss where large plates are already installed.
2. Potential damage to the lumber is too great to risk further damage to the truss.
3. The location of the truss, as installed in the customer’s structure, might dictate a non-aggressive repair like pulling out lumber and connector plates.
4. Sometimes speed is of the essence, and a shim is a quick operation.
5. Shimming can be done while the truss is still in the pack without unbanding.
6. Shimming does not require repressing.
7. Shimming on the job site is much easier to do to correct the gap problem.

Of course, the downside is the customer sees a repair more dramatically than a lumber/plate relocation.

Here is an application for installing a shim (photo used with permission – See PDF or View in Full Issue). What issues do you see?

• The shim is not coated or galvanized.
• The shim does not have a tab, however, this requirement may be determined by the truss designer if the shim can be secured.
• The shim is not secured to prevent removal. Gravity is not reasonable prevention as the shim can be dislodged during installation and use.

The Bottom Line

Don’t discount shimming as an appropriate fix. It does not replace proper assembly, but in certain situations, it can be exactly the solution you need to manage member-to-member gaps. Thanks go to my caller for recommending article topics – additional suggestions are always welcome!

An ANSI/TPI 1 3rd Party Quality Assurance Authorized Agent covering the Southeastern United States, Glenn Traylor is an independent consultant with almost four decades of experience in the structural building components industry. Glenn serves as a trainer-evaluator-auditor covering sales, design, PM, QA, customer service, and production elements of the truss industry. He also provides project management specifically pertaining to structural building components, including on-site inspections and ANSI/TPI 1 compliance assessments. Glenn provides new plant and retrofit designs, equipment evaluations, ROI, capacity analysis, and CPM analysis.