Douglas Fir carries the highest design values of the common framing species, which is why it shows up wherever a beam is working hard. Sizing one is four checks and four inputs. This page covers what those checks are, where sawn Douglas Fir beats a manufactured beam, and where it stops being worth the money.
Open the CalculatorBefore any beam can be sized, four things have to be settled. Everything after this is arithmetic.
One of these governs every beam. Knowing which one tells you whether to add depth, change grade, or change product.
Bending. The beam has to carry the moment from its tributary load without exceeding the adjusted bending stress for its grade. On solid sawn Douglas Fir beams this governs more often than it does on joists, because there is no repetitive member increase to lean on.
Deflection. Stiffness, not strength, is what people feel. Code minimum is L/360 under live load. For a beam carrying a floor above finished space, L/480 is the number worth paying for.
Shear. Short, heavily loaded beams and beams with large end reactions are where shear starts to control. It is checked every time, because short spans with heavy tributary loads are common in residential work.
Bearing. Compression perpendicular to grain at the supports sets the minimum bearing length. A correctly sized beam sitting on too little post or wall is still a failure.
A beam carrying floor joists that span 14 ft from each side, 40 psf live and 15 psf dead.
That 770 plf is the number every product option gets sized against. Run it at the span you actually have, then compare what each product needs to carry it: a solid sawn Douglas Fir timber, a Douglas Fir glulam, an LVL, a PSL, and steel. The beam comparison tool does that side by side.
Change nothing but the deflection limit, from L/360 to L/480, and the required depth usually moves one increment. That increment is the difference between a floor that passes and a floor nobody complains about.
A solid sawn Douglas Fir beam is the right call when the beam will be seen. Nothing manufactured looks like a real timber, and free of heart center stock keeps the checking under control as it dries.
A Douglas Fir glulam is the right call when the span is long, the load is heavy, or the member has to arrive dry and straight. Laminating puts the best material where bending stress is highest, so it does more with the same depth.
LVL and PSL are the right call when the beam is buried in the framing and the only question is capacity per dollar per inch of depth. Paying for a Douglas Fir timber inside a wall is a specification error.
There is no single answer without the load. Size comes from tributary width, live and dead load, span, and the deflection limit you are willing to accept. Run those four inputs through the checks below, or compare sawn Douglas Fir against glulam and LVL in the beam comparison tool.
No. A solid sawn timber is graded under the timber rules and carries the defects of one stick. A glulam is laminated from graded Douglas Fir lams with the best material placed where bending stress is highest, so it carries higher design values at the same depth and arrives dry and straight.
Different grade rules and different design values. Beams and stringers are graded under the timber tables, dimension lumber under the dimension tables, and the repetitive member increase that helps joists does not apply to a single beam.
It can. Large timbers ship surfaced green and season in place. Where the moisture content will stay high in service, the wet service factor reduces design values, and connection detailing has to allow for shrinkage as the timber dries.
No. This is preliminary sizing guidance for comparison and planning. Point loads, cantilevers, stacked walls, notches, and connection design need a licensed professional under your local code.
Results from this calculator are preliminary sizing guidance for comparison and planning. They are not engineering, not sealed drawings, and not a substitute for design by a licensed professional under your local code. Final member sizing, connections, and load paths must be confirmed for your specific project.
Bardowl Design produces structural layouts and material specifications that builders and lumberyards can actually work from. Clear scope, defined assumptions, documented output.
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