Engineered Lumber for Framers

Sawn lumber lets you get away with a lot. You can notch it, sister it, and patch a mistake with a scrap. Engineered lumber is stronger for its size because every part of it is doing a job. That is also why a cut that looks minor can take away most of what the piece can carry.

You know how to frame a floor with dimensional lumber. This guide is about what changes with engineered wood. The biggest change is that the rules come from the maker of the product in your hands. Figures below come from APA, the engineered wood trade association, and from one maker's published guide. They show how the rules work, but they do not replace the guide for your product. Each brand has its own tables, and they are not interchangeable. Sizes, spans and any field change belong to the designer of the system and the engineer of record.

What You Will Be Able to Do

• Tell I-joists, LVL, LSL, PSL, glulam and rim board apart.
• Store and handle them without hidden damage.
• Brace I-joists during installation.
• Apply web hole rules and check a hole by the numbers.
• Install bearing details: rim, blocking, squash blocks, web stiffeners.
• Know when to stop and get a written fix.

What You Are Holding

How an I-joist works. The flanges, the top and bottom pieces, resist bending, and the web holds them apart and carries shear. Cut a flange and you have cut the part that resists bending. That is why you can make a hole in the web, in the right place, but you cannot cut a flange.

Read the stamp on every piece. It tells you the maker, the series and the depth. A joist of the right depth from a different series may not carry the same load.

Storage and Handling

Damage from handling often does not show until the joist is in the floor.

• Store bundles upright on a flat, well-drained surface, on spacers, and off the ground.
• Keep them covered and dry. One maker says these products are for dry use only.
• Keep joists vertical when you move them, and avoid big bows.
• Do not put a load on a joist that is lying flat.
• With glulam, leave the wrap on until the beam is covered. Slit it on the bottom so water can drain, and seal any cut ends.
• Do not use a damaged I-joist, and do not repair one in the field unless the maker gives you a written repair.

Bracing I-Joists

An I-joist is tall and narrow, so it rolls over easily until it is held in place. The risk is highest before the sheathing goes on.

Warning: Do not let anyone walk on I-joists until they are fully installed and braced. A joist that is not braced can roll under one person. Install end blocking and bracing as you go, not at the end, and use fall protection where the floor is open.

The rules below come from one maker's guide, and they match common practice.

1. Install and nail all hangers, rim board and blocking at the supports as the joists go in.
2. Use at least 1x4 temporary bracing, at 8 feet on center, with two 8d nails into each joist.
3. Lap the ends of the bracing, and anchor it to sheathing already nailed to the first 4 feet of joists, or to a braced end wall.
4. Brace cantilever ends at both flanges.
5. Take bracing off only as the sheathing goes on.

Material stacks. Never stack sheathing or other material on unsheathed I-joists. Stack only over beams or walls. A bundle of OSB is a concentrated load the joists may not be able to take before they are braced. Do not overload the sheathed floor either.

Bearing and Load Details

Every I-joist has to be supported and held at its ends.

The plans may require more bearing than these minimums.

Why squash blocks matter. An I-joist's web can only take so much load straight down. When a bearing wall or a post sits above a joist, the load has to get past it without crushing the web. A rim board, a blocking panel, or a pair of squash blocks does that job. Cut squash blocks about 1/16 inch taller than the joist, so that the load goes into the block, not the joist.

Web stiffeners. Check your product guide for where they go. Common cases are high reactions at supports, some deep joists, and hangers whose sides do not hold the top flange. A stiffener is cut about 1/8 inch short of the clear space between the flanges, and it fits tight to one flange.

End cuts and nails. Do not bevel-cut a joist beyond the inside face of the wall. To avoid splitting a flange, start nails at least 1-1/2 inches from the end of an I-joist.

Holes in I-Joists

Trades will cut your floor if you let them. Holes are allowed in the web, by the rules. The list below is from APA's guide for Performance Rated I-joists. Your maker's table sets the distances for your joist.

1. Never cut, drill or notch a flange.
2. Center field-cut holes in the web when you can.
3. A round hole can be as big as the clear space between the flanges, less 1/4 inch. Keep at least 1/8 inch between the hole and the flange.
4. The side of a square hole, or the long side of a rectangular hole, can be no more than three-quarters of the largest round hole allowed at that spot.
5. Between two holes, the clear distance must be more than twice the size of the larger one.
6. No more than three maximum-size holes per span.
7. The distance from a support comes from a table, which depends on the joist, the span and the hole size. Bigger holes usually stay farther from the supports.
8. A 1-1/2-inch hole can go anywhere in the web, as long as it still meets the spacing rule.
9. Knockouts do not count as holes.
10. On a joist with more than one span, use the longest span to find the hole location.

Worked example. A joist is 11-7/8 inches deep, with 1-1/2-inch flanges. One trade wants a 6-inch round hole, and the HVAC installer wants an 8-by-6-inch rectangular hole nearby.

1. Clear web: 11.875 - 3 = 8.875 inches.
2. Largest round hole: 8.875 - 0.25 = 8.625 inches. The 6-inch hole fits the depth.
3. Largest side of a rectangular hole, if the table allows that full round hole at this spot: 0.75 x 8.625 = 6.47 inches. The 8-inch side does not pass.
4. If the rectangle changes to 6 by 6 inches, its side is under the limit.
5. Spacing between the holes: more than 2 x 6 = 12 inches of solid web, edge to edge.
6. Both holes still need to meet the table's distance from the support.

Cut rectangular holes with care. Drill the corners, or round them slightly, and do not overcut. An overcut corner starts a crack.

Walk the trades through this before they start. It is much cheaper than a repair letter.

LVL and Other Beams

LVL is usually a beam, so a hole or notch hits a part that is working hard. One maker's guide allows these field actions: cutting to length, ripping or trimming only as the guide shows, and drilling holes as the guide shows. No other cuts, notches or drilling.

Its hole rules show how tight this can be:

• Round holes only, in the middle third of the depth, away from the supports.
• A maximum of 2 inches in beams 9-1/2 to 24 inches deep.
• No more than three holes in any 4-foot section.
• These apply only to uniformly loaded beams. A beam with a point load or a cantilever is outside the detail.

Multi-ply beams. Two or three LVLs side by side have to act as one beam. If one ply carries all the load from one side, the nails or bolts must pass that load across. The schedule depends on the number of plies, how they are loaded, and whether the load comes from one side or both. A beam carrying joists on one side often needs more fasteners than one loaded from above. Use the schedule on the plans or in the product guide. Do not "just add a few nails."

Bearing. A beam's end load can crush a stud stack if the stack is too small. The plans show the number of studs under each end, so build what is shown. A beam moved a foot may change the point load on what is underneath.

Glulam

• Top. Some glulam beams are unbalanced, with stronger wood on one side. These are stamped TOP. If you put one in upside down, it has less strength than the design assumed.
• Camber. Many glulams are built with a slight arch, so they flatten out under load. Install the camber up, unless the plans say otherwise.
• Cuts. Treat any notch or big hole as a design question, not a field call.

Rim Board

Rim board closes off the ends of the joists, carries wall loads down, and ties the floor to the wall. Holes in it have their own limits, and one rule is to keep them away from openings and heavy loads below. Do not let a dryer vent or a pipe chew through it without checking your guide.

What You Can Decide, and What You Cannot

Get any field fix in writing, and keep it for the inspector. A verbal okay from the lumberyard does not hold up. When a repair letter comes, follow it exactly.

Check Your Understanding

1. A joist is 9-1/2 inches deep with 1-3/8-inch flanges. What is the largest round hole by the depth rule?

9.5 - 2.75 = 6.75 inches clear. 6.75 - 0.25 = 6.5 inches.

2. A trade saws an opening in a web that fits the chart, but the saw kerfs run past the corners. Is it fine?

Not yet. An overcut corner can start a crack, even when the size is right. Get a written answer from the maker or engineer.

3. An electrician wants to notch a top flange 1/2 inch to clear a box. What do you say?

No. Flanges are never cut or notched. Move the box, or use a web hole.

4. A pallet of sheathing is going to land on the middle of a just-set I-joist bay. Where should it go?

Over a beam or a wall, and only after bracing is on. Never on unsheathed I-joists.

5. A glulam stamped TOP shows up with its stamp facing the floor after it is set. What do you do?

Stop before it is loaded. Turn it over, or call the engineer if that cannot be done.

Key Takeaways

• Rules come from the maker. Keep the guide for your product on site.
• Never cut or notch an I-joist flange. Holes go in the web, by the chart.
• Nobody walks on I-joists until they are braced.
• Stack material over beams or walls, not on unsheathed joists.
• Loads from above must get past the joist through rim, blocking or squash blocks.
• Fasten multi-ply beams to the schedule, and install glulam top up.
• Get every field fix in writing.