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erick | Dec 12, 2005 11:08pm | #9. Ditto, with a properly sized beam down the middle doubled 2X6's should be fine. However , instead of sistering and worrying about properly connecting, they seem to still be adequate @ 8" o.c. (HF #2), basically dropping one in between, given 3/4" glued & screwed plywood.
But the 2015 IRC included a new one (Table R507.5) that will make it easy for deck builders to spec a joist size for a given span and joist spacing. The table includes spans for common lumber species used for deck framing like southern pine, Douglas fir, hem-fir, redwood, western cedar and other species. The table accounts for wet service ...
The sag could be reduced or eliminated by installing king posts, or Leom could sister 2x8s to the 2×6 joists to “roughly triple” the load-bearing capacity of the ceiling. “Since this isn’t a floor, then the allowable deflection tables don’t really apply,” adds Jigs-n-fixtures.
This revealed that the attic was built on 2×6’s with occasional 2x4s sistered to help level the floor above. The 2×6’s are old and is true 2″ x 6″ lumber. The bedroom underneath with the exposed ceiling is 14ft x 13-16ft. My question. I’m concerned that the attic is supported by 2×6’s every 16″ on center.
Sistering two new 2x10's produces a beam 3" wide, while a new 4x10 is actually 3 1/2" wide. Sistering a new 2x10 to an old one (full 2"), which is what I'm doing in my bathroom, does produce a beam 3 1/2" wide, identical to a modern 4x10. But that's just identical for size. In my case, the sisters are select structural, and the original joists ...
For example, a double 2×8 beam can span 8-ft.-9 in. when the deck joists are 6 ft. long. When the deck joists are 8 ft. long, the beam can span 7-7. When building a deck with 7-ft. joists, you know the beam can span somewhere between 7-7 and 8-0, but you don’t know exactly where. Check with your local code official, or simply drop back to ...
Begin with the difference in span for a given header configuration between the building width on each side of the actual building width. At 20 ft., a single 2×8 can span 3 ft. 11 in. At 28 ft., it can span 3 ft. 5 in., so the header span difference is 6 in. over 8 ft. To find the difference per foot, divide 6 in. by 8 ft.:
ENGINEER10 | Oct 27, 2010 06:03pm | #22. Both 2x6 and 2x8 are undersized. For a 16' span, No. 2 SP wood, a 2x6 can carry 10 psf and a 2x8 carries 20 psf. Sistered together they can carry 30 psf. This is based on bending strength only not deflection, therefore a load larger than that will cause collapse.
In conventional deck framing, half the joist-span load bears on the ledger and half on the beam. When a joist cantilevers the full 1:4 ratio, the load on the beam increases by 50%. For example, the load on a beam from a 10-ft. joist span with a 2-ft. 6-in. cantilever is the same load as a 15-ft. joist span with no cantilever.
Example: A deck with a beam located 12 ft. 6 in. from the ledger, framed with 2×10 joists at 16 in. on center. Check 1: The allowable overhang/maximum cantilever is 3 ft 5 in. per the DCA 6 table and 3 ft. 6 in. per the 2018 IRC table. Check 2: 12 ft. 6 in. / 4 = 3 ft. 1 in.