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post #1 of 15 Old 12-14-2012, 05:17 PM - Thread Starter
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I have been reading several build over the last few months this is my first post. I have a large space in my basement that i am trying to plan a dedicated room in. I would love to make it a completely decoupled room by building a room in a room. But my big concern is my floor joist from the first floor will run the long side of the theater. My floor joist are 2 x 10 and span 15 ft onto a steal beem in the middle of the house. I think i can build the back and front walls and position the ceiling joist in between the above floor joist to keep my ceiling height minus maybe 1/4 of an inch. I want to extend past the center beam by 8 ft to 23 ft to get close the ceiling height x 1.6 x 2.6 golden rule. I am wondering if i can span 23 ft using 2 x10 and support the ceiling. I will have to notch over the beam what ever distance i stay away from the above floor so i don't touch that beam to stay decoupled. I am thinking i should be fine if my first floor can sit on a 15 ft span with the weight of everything about it that i could stretch the span with the only weight being the drywall. You expert framers please help me out. Can i do this ?
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post #2 of 15 Old 12-14-2012, 06:07 PM
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You should be able to span 23ft. without any problems. A 2x10 of most species will span over 26 feet.

There will be significant deflection, but within standards.

Tim
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post #3 of 15 Old 12-14-2012, 06:09 PM - Thread Starter
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Originally Posted by Mr.Tim View Post

You should be able to span 23ft. without any problems. A 2x10 of most species will span over 26 feet.
There will be significant deflection, but within standards.
Tim

deflection ?
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post #4 of 15 Old 12-14-2012, 06:17 PM
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Sag in the middle.

Somebody smarter than me could tell you how much (an inch.. two inches). Would depend on what species lumber you use.

Tim
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post #5 of 15 Old 12-14-2012, 06:22 PM - Thread Starter
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Originally Posted by Mr.Tim View Post

Sag in the middle.
Somebody smarter than me could tell you how much (an inch.. two inches). Would depend on what species lumber you use.
Tim
what if i used engineered joist instead of just 2 x 10
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post #6 of 15 Old 12-14-2012, 06:52 PM
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I'm not an expert, but I have a resource for you. The American Wood Council has an online calculator. http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

You'll need to know or approximate a number of variables for input into the calculator: the species and wood grade you can get from your supplier - I used No 2 Spruce, as that was readily available here in Atlanta; your spacing (presumably 16"); and the deflection limit. There are a few other inputs, which I think are self-explanatory.

The difficult ones (requires math) are the dead load (you won't need live load) and deflection limit. Dead load is the weight of the drywall and fixtures or other structures hanging form the joists. 5/8 drywall weighs about 2.2 pounds per square foot (psf). You can add up the total dead load you expect, though it's probably less than the minimum the calculator will allow, so it's building in some extra allowance for you. Deflection limit is given as a fraction (L/240 or L/480 etc). The larger the denominator, the smaller the deflection you are specifying. You may want to play with the calculator to get an idea for how much is too much deflection. The L component of that fraction is the designed span - 23ft in your case. 23ft/240 is just under 0.1 feet. If you were to build to that deflection, the center of the ceiling should be within that height of the edges - around 1 inch.

Plugging some numbers into the calculator, making some assumptions on your behalf, it looks to me like you can make it, depending on your tolerance for deflection. I'm a little surprised, to be honest. I had imagined a span that long would need an engineered support solution.

Naturally, I am not an engineer or architect, but I think I have a fair grasp on this topic. I used this same approach in my build, but haven't gotten to a point where I can check the validity of my calculations.

Fred
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post #7 of 15 Old 12-14-2012, 07:34 PM - Thread Starter
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Quote:
Originally Posted by HopefulFred View Post

I'm not an expert, but I have a resource for you. The American Wood Council has an online calculator. http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
You'll need to know or approximate a number of variables for input into the calculator: the species and wood grade you can get from your supplier - I used No 2 Spruce, as that was readily available here in Atlanta; your spacing (presumably 16"); and the deflection limit. There are a few other inputs, which I think are self-explanatory.
The difficult ones (requires math) are the dead load (you won't need live load) and deflection limit. Dead load is the weight of the drywall and fixtures or other structures hanging form the joists. 5/8 drywall weighs about 2.2 pounds per square foot (psf). You can add up the total dead load you expect, though it's probably less than the minimum the calculator will allow, so it's building in some extra allowance for you. Deflection limit is given as a fraction (L/240 or L/480 etc). The larger the denominator, the smaller the deflection you are specifying. You may want to play with the calculator to get an idea for how much is too much deflection. The L component of that fraction is the designed span - 23ft in your case. 23ft/240 is just under 0.1 feet. If you were to build to that deflection, the center of the ceiling should be within that height of the edges - around 1 inch.
Plugging some numbers into the calculator, making some assumptions on your behalf, it looks to me like you can make it, depending on your tolerance for deflection. I'm a little surprised, to be honest. I had imagined a span that long would need an engineered support solution.
Naturally, I am not an engineer or architect, but I think I have a fair grasp on this topic. I used this same approach in my build, but haven't gotten to a point where I can check the validity of my calculations.
Fred[/quot"

thanks i will have a look
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post #8 of 15 Old 12-15-2012, 01:52 AM
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Originally Posted by scottn83 View Post

I will have to notch over the beam what ever distance i stay away from the above floor so i don't touch that beam to stay decoupled.

Be careful then when looking at the span tables, notching reduces the effective size. You could sister additional material to the sides of the the notched ceiling joist to improve the situation but I couldn't tell you how much is needed.
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post #9 of 15 Old 12-15-2012, 07:11 AM
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Seems that i-joists would be the best way to go. I'd suggest finding a supplier that can get design calculations for ceiling joists. The published span tables usually only cover floor and roof applications.

I found a document that has the equations to calculate deflection. Look at page four of this pdf.

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post #10 of 15 Old 12-15-2012, 07:31 AM
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Depends on how important deflection is to you. A 2x10 will be fine and the deflection will be less than an inch at 23 feet with a dead load <5psf.

When I did my theater ceiling there was noticeable deflection when I was framing the soffits. THat is, I could notice it when I was framing. You could never tell just from looking at it.

Engineered lumber will give you less deflection and is lighter to work with. They have their own span charts that are available from the manufacturer.

Tim
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post #11 of 15 Old 12-15-2012, 12:39 PM - Thread Starter
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thanks everyone i think i will try the engineered joist direction that way a i can get a pro to tell me what i can use
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post #12 of 15 Old 12-19-2012, 03:27 PM - Thread Starter
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Just had another idea after looking and studing and measuring and on an on. I think I could sandwitch 3 2 x 12 x 18 build a beam and set on post inside the side walls. Then hang 2 x 8 x 15 between the beam and the 2 x4 wall. Then there would only be an inch notch to go around a water pipe. then a shorter span on the other side of the beam. here is a drawing not to scale let me know if you think that is an option ]
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post #13 of 15 Old 12-22-2012, 08:55 AM
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That looks like it would work.

Why are you doing room in room rather than using clips and channel?

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post #14 of 15 Old 12-22-2012, 10:03 AM - Thread Starter
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i thought that having the ceiling completely separated from the rest of the house it would make it easier to frame around some duct work and beams in the exciting space
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post #15 of 15 Old 12-22-2012, 01:28 PM
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Quote:
Originally Posted by petew View Post

That looks like it would work.
Why are you doing room in room rather than using clips and channel?

+1 of I had my time again I'd do this - takes less space and to be frank is easier (now having seen it in action)

We have things called hyJoists in Australia (an engineered joist which is ply with 2x4 to make an I joist sort of thing), I've seen them heavily notched but with little horizontal "braces" under/and or over the notch

When I put mine in I'lll need to cut some pretty large notches due to some plumbing issues. I'll brace around it with ply and then the first layer of sheeting will be structural (19mm) ply which will further spread the load.

.....but as I said, just do clips

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