I’m looking to build a 2-car detached garage that’s 24ft wide with a loft above for storage. I’ve been searching and I can’t seem to find any lumber that spans 24ft. If I had 2x6 (or 2x8 or 2x12) that are 20ft long (longest I can find) can I stagger them and attach two together? There would be 20ft of overlap that’s attached and 2ft on either side that’s just a single board. Is this safe? Or do I have to do more of a truss system to support the beams?
I suppose there must be a way you could splice dimensional lumber and make a longer span, but... why?
Have a look at wood I-joists. Boise Cascade (BCI), LP Building Products (SolidStart) and Weyerhaeuser (TJI) are three options widely available in the US. (photo below from lpcorp.com)
As a single point of reference, a BCI span table shows spans up to or exceeding 24 ft with joists 11-7/8, 14, or 16 inches deep with spacings of 12, 16, 19.2, or 24 inches on center. You'll have to consult the table yourself to see the effects of joist family, spacing, allowed deflection, and loading.