Ceiling Joist Span

[pioneergal]

Once again we need help from people in the know!  

We have an area .....kitchen / dining room that clear spans from inside wall to outside wall  19 feet.

A few people have told us that we need to use 2 x 12's for that area to prevent any future problems in the roof system but then 1 or 2 others said we would be okay with 2x10's.

We have little or no snow or ice in this part of Texas and this area of the attic will not be used for storage if that information will aid someone in answering our question.

DH was checking the AWC Span Chart  plus another lumber span table for a 2x10  span and they both gave the span of that size joist as 20 ft 9 inches.

Even tho the chart  gives this span for a 2x10 are we making a gamble by not going with the 2x12's ?

Money is an issue but we would rather spend it once and do it right rather than have repairs later.

On the other hand, if there is a way we can save but be safe we would like to do so.

I hope that this all makes sense.........

We're not trying to cut corners and be cheap but only trying to be smart in spending and making decisions.

Jackie

[glenn kangiser]

John posted a span calculator in the free stuff that is not as generous as the one you are using unless I'm not setting it right for your situation.

Using douglas Fir #2  - 19'1" on 24" centers -  Using 2x10 on 16" centers shows 20'2"

http://simurl.com/kahzuf

The 20  wide uses 2x12's but has a loft above.

[harry51]

Here are a couple of things to consider:

In order to get an accurate answer on joist sizing, the live and dead loads involved should be known, as well as the length of span. If the calculator doesn't require that input, I would consider the answer just an approximation. So the weight of all the material above the joists, the weight of the joists themselves, the weight of the ceiling material below must be determined, and the live load requirement for the building added to that, and that number must be applied proportionally to the area in question to arrive at the proper joist size.

It's possible that either 2x10 or 2x12 lumber would be strong enough; the problem is bending, or deflection. Deflection in finished areas is usually limited to 1/360th of the span in order to prevent cracking and sagging of ceilings, etc. For instance, a Douglas fir #2 2x10 is rated to support an evenly distributed load of up to 1053lbs across a 19' span, but will only support 820lbs and still remain within the deflection limit. So it may be money well spent to buy the 2x12's for that reason.

Don't forget about X braces or blocking between the joists to keep them vertical, very important on deep joists with long spans.  Another thing is that depending on the kind of roofing, another layer (or more!) may be added on top of the first in the future, and that could be enough weight to move the framing around if it's marginal in the first place. So, you get a new roof in 20 years, and suddenly ceiling nails and joints start popping!

Around here, a 2x10x20' costs $19.93, a 2x12x20' costs $25.70. So depending on how many you need, it may not add up to a lot more money to go 2x12.

BTW, I got those prices using Home Depot's Contractor CD. It's a freebie that catalogs all their merchandise, and updates the prices at your local store via the 'net when you ask it to. It also has some labor estimating tools and a way to set up a costing database for different projects. I've found it to be pretty handy, and the price was right!

Hope this helps!

[PEG688]

 Jackie  I'd go with the 2x12's , or a "I" joist ( eng. lumber/ joist) if your not using truss's in this area.


    Use collar ties( 2x6's) on your rafters  ,and you could / should do a "Rat Run " down the center with a strong back . A "L" 2x4 flat nailed to a 2x4 on edge , pull your 1st  joist  streight, and pull O.C. layout from it ,( so all your joist's are 16" or 24" OC from one another , down the center of the room ) nail the strong back to the top of your joist's w/ 16d sinkers .  You did say the attic will not be used as floor space so the strong back won't be in the way of anything if I understand you correctly .

 Good luck , PEG