Aug 30, 2015

Floor framing and joist blocking- research and planning.

As I’m starting to research the next step, building the floor box and joist, I am once again learning that different builders do things differently, not necessarily right, but differently :) Since I’m not a builder or a structural engineer, I can only try and use my common sense and Google—a bad combo.

First, I’ve noticed there are many examples online of how a floor is built. They all look good, but I don’t think they’re all correct. I recently learned that there’s a wood standards company that publishes the numbers for how far a wood board can span. All that depends on the wood type, and wood size-- 2x4, 2x6, 2x8… and live/dead loads it needs to carry. Here’s a handy calculator:
http://www.awc.org/codes-standards/calculators-software/spancalc

SIDE NOTE: I conservatively thought that “wood span” referred to how far the whole solid piece of lumber can go. So say a 2x8x8 has one span value and 2x8x10 has a different one. Thanks to this site, I’ve learned that the meaning is different:
http://bct.eco.umass.edu/publications/by-title/understanding-loads-and-using-span-tables/

The “span” is the distance that a piece of 2xX lumber can span between two supports. So if you have say a 2x10x16 piece and it spans 3 beams which it rests on, then it actually has a 5.3’ span between each beam—not a 16’ span.

Knowing that, I now realize I set myself up to use 2x10s when I could have gotten away with 2x8 for my 6’ spans. A waste of about $50, but I already bought the lumber, so here’s to a solid floor :)

I have also noticed that some build their floor with double rim joists. After doing more research and talking with my city inspector, I have decided to go with the single rim joist. One final thing I’m struggling with is joist blocking. You see some images on Google and the joists are not blocked at all. Some show a “girder” down the middle to break a joist span. I don’t think I need one cuz my spans are short and wood is big—he he he. But as far as blocking, I see 2 options.

1. Block the 2 cavities closer to the perimeter of the floor

2. Block all the cavities (need extra wood)

Have not yet made that decision.

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