November, 2008
Feature
Inspection News and Views from the American Society of Home Inspectors



Code Corner: Engineered Lumber

BILL SUTTON

Engineered lumber can support greater loads and longer spans than the more conventional dimensional lumber, but good performance requires proper handling and detailing. 

LVL (laminated veneer lumber):
On many newer homes today, laminated veneer lumber (LVL) has displaced both steel- and glue-laminated timbers for ‘large span’ applications. 

The advantages: You don’t need a crane or a welder.  The most common LVLs come in l-½" or l-¾" wide plies that are relatively lightweight and easy to handle. The clips, hangers and other connectors are readily available and behave much like conventional lumber hardware.

Therefore, as demand increases, we as home inspectors can expect to see more of these LVLs on both newer houses and additions.  Although LVLs may handle a lot like conventional lumber, you should be aware it’s not the same “stuff.” And one of the more important connections we should look for, that’s often done insufficiently in the field, is the connection between the plies. Manufacturers are very specific about both nailing and bolting schedules for fastening plies.

Nailed and bolted connections:
For laminating l-¾"-wide LVLs up to three 12-inch-deep plies, look for two rows of 16d nails spaced 12 inches on center.  The rows should be nailed from both sides with the spacing staggered.  For three plies over 12 inches deep, look for three rows of 16d nails, again 12 inches on center, both sides with a staggered pattern.  For laminating four or more plies (generally, it is not recommended to exceed four plies), look for two rows, three inches from the top and bottom of ½"-diameter through-bolts with fender washers on both faces, every two feet on center, with a staggered pattern, in addition to the regular nailing schedule specified above.  Other details we should look for include proper post caps, splices and beam pockets.

Post Caps:
Load-carrying beams must have a minimum bearing length at each support. For this reason, most manufacturers of engineered lumber recommend steel post caps for wood posts or a steel-bearing saddle for steel posts — both with side plates on both faces — to prevent the beam from twisting or rotating at these supports.

Splices: Splices between piles should be staggered and should fall within the  supported bearing length of a post.  If this isn’t possible, the splice should fall in the middle between supports if the manufacturer concurs.  Too often, the splice is placed just slightly off bearing where it can shift, causing the beam to sag.

Beam Pockets:
Codes require protection of untreated foundation beams from concrete.  They usually specify a ½" separation (gap) from all concrete surfaces.  Some municipal building inspectors allow or require some type of vapor retarder between the wood and concrete (e.g., 6 mil poly-vapor barrier, foam sill-seal or a pressure-treated (p.t.) set block in the beam pocket).  Non-p.t. wood should not be grouted tight into the pocket because of the possibility of rot.

Truss Joists:
The truss joists (LPI joists) may have Gang-Lam, LVL flanges and solid, oriented stand board webs. They’re manufactured with no camber, eliminating possible upside-down installation. Some of the common “red flag” areas we should look for include the following conditions, which are NOT permitted.

Red Flags


Don’t use dimensional lumber for fastening to truss joists such as band joists. Dimensional lumber, unless it’s kiln-dried, often has a higher moisture content. Therefore, when the shrinkage occurs as it dries, connection problems often result.

Don’t put holes too close to supports. Use only manufactured knock-out areas or stay within the limits of the manufacturer’s web-hole specifications.

Don’t overcut holes and damage flanges. (If the web hole size and location is in conformance to the specs, but is overcut and damages or penetrates the flange, it’s defective.)

Don’t cut or notch or drill any section of the flange.
Don’t use oversized nails or hammer on flange and damage the joint. Usually, two 8d nails, l-½" minimum from end of joist to nail, are required for proper connection.

Don’t cut beyond the inside edge of the bearing (don’t scarf-cut ends).

Don’t support joists on web.

Another common deficiency to look for is a loose bottom flange pulling away from the web. This condition may occur during erection when framers might be hitting the top of joists and/or inappropriate loads are fastened to the bottom flange.

In conclusion, it is impossible for us to know or even carry the manufacturer’s specs (span charts, installation details, etc.) for all the different engineered lumber out there. Therefore, if you see any of these ‘red flag’ areas or other deficiencies and have concerns or questions, it would be prudent to advise your client accordingly.  
Most manufacturers of engineered products provide technical support and are usually glad to help you if follow-up is necessary.  However, you must know the manufacturer or distributor (which we often don’t) to be able to solicit their assistance.  Finally, we should have sufficient knowledge for inspecting engineered lumber or should recommend a qualified structural engineer to follow up with our clients if questions or possible defects are apparent.


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Would you Like to Read More About Structural Considerations?

There’s a wealth of information available here.

July 2007: “Inspecting Wood Trusses,” by Garet Denise, P.E.

August 2003: “Structural Considerations of Floor Framing and Load  Distribution,” and “For Want of a Squash Block,” by JD Grewell.

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