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Old 05-27-2010, 04:40 PM   #1
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Doug Fir "checking"


Hello,

I am building a 10 x 14 room with storage space above it out of 2x4 joists and 2x6 headers. In addition to the 2x6 headers I have an additional 2x6 support joist (14 ft) that cuts down the maximum 2X4 joist span to 5'10" . The grade of wood is doug fir stud or btr. Using the AWC (american wood council ) joist calculator I have determined the design is solid.

However I have noticed in several of the beams a "checking" that is occuring in them. There is little to no deflection happening even with live loads ( i got on top to work on subfloor).

I have been reading that this is common to the species. However I can't find anything about how checking effects the structural integrity of the wood.

Does anyone know more about this subject?

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Old 05-27-2010, 04:49 PM   #2
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Doug Fir "checking"


All structural grade species of wood check, due to changes in moisture content. The allowable stress and modulus of elasticity in the tables assume normal checking, so there should be no structural concern on your part. This assumes normal checking, rather than severe damage due to defective lumber.

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Old 05-27-2010, 05:06 PM   #3
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Doug Fir "checking"


what is normal checking? Some of the checking I have is very long.



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Old 05-27-2010, 05:20 PM   #4
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Doug Fir "checking"


Post a picture of the checking, then we can all have a learned discussion about how normal your checking is.
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Old 05-27-2010, 05:39 PM   #5
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Doug Fir "checking"


Ah my pictures didn't come out? Thats funny they are displaying here. Here are a couple in html format.

http://i945.photobucket.com/albums/a...u/IMG_0414.jpg

http://i945.photobucket.com/albums/a...u/IMG_0416.jpg
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Old 05-27-2010, 06:03 PM   #6
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Doug Fir "checking"


When doesn't it happen. If you wax the ends while drying and it is free of heart wood you may have a chance but it usually does not effact the structural integrity. Kinda gives it character
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Old 05-27-2010, 11:31 PM   #7
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Doug Fir "checking"


I hope it’s light weight storage. Your 2x6x14’ will carry about 47# per lin.ft. Divided by 5’ of the 10’ span, that’s about 9# per sq.ft. Minus the 5/8” ply at 1.8# per sq.ft., leaves you with 7# per sq.ft. I don’t have the figures on how much the 2x4’s support themselves in the middle 5’ to increase the 2x6’s load, though…..



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Old 05-28-2010, 09:35 AM   #8
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Doug Fir "checking"


So once I add the 5/8 gypsum, mineral wool, and 1/2 " plywood then you are saying it won't even hold 2 lbs/ sq ft. Should I reinforce with one more 2x6 on top or just start over with 2x6s then? I should have found the joist calculator earlier.
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Old 05-28-2010, 09:44 AM   #9
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Doug Fir "checking"


What distance are the 2x4's spanning ?
You then added one 14' 2x6 across the middle ?
A 2x6 is rated to span around 12' depending upon grade & species 20/10psf L360
Since its above the 2x4's it doesn't really cut down on the span like a beam underneath does
Its acting as a strongback I believe, which helps

2x6's headers ? Or ledger boards on the sides ?

I would never have used 2x4's if you wanted storage above
I would have put 2x6's across the 10' span
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Old 05-28-2010, 11:07 AM   #10
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Doug Fir "checking"


looks like i am off to the lumber store. it pays to do research and it hurts when you don't .
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Old 05-28-2010, 08:14 PM   #11
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Doug Fir "checking"


And pick up a lot more lag screws, but don't weaken the shear connection by counter-sinking the heads and washers.

Dave-- "Since its above the 2x4's it doesn't really cut down on the span like a beam underneath does
Its acting as a strongback I believe, which helps" ----------- Sorry, wrong. This is exactly one of the purposes of his 2x6 (1/2 of a strong-back), to reduce the span of ceiling joists or support roof framing. If it is above or below the ceiling plane doesn't affect it's strength. You need to stagger the sides of real connectors and keep the 2x6 from over-turning at the ends, adding a 2x4 to the bottom to act as a beam or true strong-back, though.

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