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Old 03-02-2010, 10:02 PM   #1
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Attic Joist Size


I have about 500 Square Feet of attic space that I would like to convert to an office. the joists are 2x8. Under the attic floor are the master bed room and the kitchen. I'm told that the joist should be 2x10 to support the load.
What should I do?

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Old 03-02-2010, 10:05 PM   #2
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Attic Joist Size


What is the span distance for the joists ?
Who told you they need to be 2x10 ?

What load is going up there ?
Just furniture.....desk..pc etc ?

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Old 03-02-2010, 10:34 PM   #3
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Attic Joist Size


I will have Just TV, furniture.....desk..pc etc
The distance for the joists between 14 and 15
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Old 03-02-2010, 10:44 PM   #4
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Attic Joist Size


Any idea
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Old 03-02-2010, 10:51 PM   #5
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Attic Joist Size


Between 14 & 15' ?
Measured from wall to wall ?
Are they 16" OC or 24" OC ?
For 15' wide the attic area is 33' long for approx 500 sq ft ?

2x10's would work 16" OC for up to about 16' depending upon wood species & grade

2x8's would probably not work...depends upon the wood species & grade & EXACT span distance

Who told you they need to be 2x10's ?
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Old 03-02-2010, 11:07 PM   #6
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Attic Joist Size


The attic area is about 24 feet by 28 feet= 672 SFt. The size of the joist is 2X8 inches I don't know the length of the joist as they are under the insulation. What does 16" OC or 24" OC mean? A friend who is a builder suggested the 2X10 joist for better support.
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Old 03-02-2010, 11:10 PM   #7
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Attic Joist Size


Te distance between the joists is about 14 inches and 15 inches.
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Old 03-02-2010, 11:11 PM   #8
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Attic Joist Size


The way you size a joist is based on the distance from one support (wall) to another support (wall)
Without knowing the distance its impossible to size a joist
16" OC - on center = joists 16" apart....or 24" OC = 24" apart
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Old 03-02-2010, 11:28 PM   #9
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Attic Joist Size


What I did is to measure from wall to wall and I found 28 feet for one side. Then from wall to wall and found 16 feet on the other side. Then I measured the eighth and the width of the joists and they are 2X8 inches. They are separated between 14 and 15 inches apart. I will find out more to make sure that I am correct. Thanks.
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Old 03-02-2010, 11:37 PM   #10
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Attic Joist Size


Is this measuring downstairs - between the support walls ?
You've given 3 different "measurements" now

Space to build ~500 sq ft
Space 672 sq ft = 24 x 28
and now 16x28 = 448 sq ft

To span 16' you really need 2x10's
Is there a basement below & will the floor joist support exist all the way down to the foundation/support of the house ?
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Old 03-02-2010, 11:57 PM   #11
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Attic Joist Size


The house is a split foyer with 2 car garage, a laundry room, a full abth, and two bed rooms all located in the basement. On top you have a dining room, a master bed room, two other bed rooms, and two baths. Then you have the attic with a lot of space. But I need to convert only the 672 sq ft to an office/tv room space.
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Old 03-03-2010, 12:30 AM   #12
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Attic Joist Size


The last I checked, Birmingham has a building code. Conversion of attic space to living space requires compliance with code for safety, including issues such as egress, wiring, floor loading, insulation, air circulation, windows etc. I am assuming you plan to build to code, before you start designing this job you need to check with the local code enforcement official to get the latest building code, and find out what the requirements are. The required joist size is only one of many issues you need to address.
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Old 03-03-2010, 09:51 PM   #13
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Attic Joist Size


Thanks. I will first check with the city.

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