A load of questions on home beams
BY TIM CARTER Tribune Media Services
DEAR TIM: Can you tell me a few things about the wood beam I uncovered while doing a plumbing repair? How is it possible for this beam to carry the load of everything above it? I’m worried it might not be large enough. How do I know if the beam is sized correctly? What’s involved in calculating the right size of a beam? It seems pretty complex. — Randy C., Montrose, Colo.
DEAR RANDY: Without seeing the plans for your home and being present to do a physical inspection of my own, there’s not too much I can tell you about that wood beam.
If your home has been lived in for some time, and if you’ve gone through several winters with heavy snow on your roof, you’re probably fine and there’s no imminent danger of collapse.
Wood beams are indeed complex.
Actually, any beam is fairly complex, whether it’s made from wood, steel, concrete or some combination of materials. Structural engineers specialize in beams like this. It takes years of schooling and additional years of practical day-to-day experience with beams to understand their limits and what goes into the calculations to size them properly.
Span is defined as the distance between two consecutive points of support, such as a column or a wall. As the span of a beam increases, the amount of weight it can carry is reduced. Engineers, architects and builders calculate the necessary size of a wood beam using span charts. There are computer programs that contain span tables that indicate the load capacity of different wood beams. Some lumber mills publish them in booklet form. These are not to be used by do-it-yourselfers, as many things can go wrong if you don’t put in the correct data when sizing a beam.
The beam in your house is successfully carrying the load because it was sized correctly, and it was made from material that can handle the loads above. You’d be shocked at how strong certain species of wood are, especially the highest grade of Douglas fir.
You can also get modern wood beams made from engineered lumber. Beams are made from lumber strands that are glued together. I used this type of beam material in the last home I built. They performed well.
You could even make a beam yourself by gluing together flat 2-by-4s and 2-by-6s of traditional framing lumber. I wouldn’t recommend doing this yourself, but I would tell you to purchase a beam made like this from a lumber company. They build the beams using the correct glue and lumber, and they make sure the beam is clamped the correct amount of time to get the maximum adhesive bond.
If you need beams sized for your home, don’t allow anyone to guess. Hire a structural engineer to do the calculations. It’s a job for professionals.
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