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 DIY Chatroom Home Improvement Forum Remodeling Attic Space
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09-21-2009, 12:34 PM   #1
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## Remodeling Attic Space

I have a one story home which used to have a somewhat finished attic room. The attic was poorly built so we took it all out. Now that I have a big empty space I want to be able to build a new bedroom making sure that existing structure will support it.

Attic space is 25 x 30
Bedroom dimensions will be centered at 15 x 24
Existing floor joists are 2x6 16" oc and roughly span 12 feet on both sides with supporting wall below.
I will have knee walls all the way around the room approximately 5 feet away from exterior walls.

I already know my floor joists are not strong enough so I was thinking about sistering a 2x8 next to each existing joist. According to a floor joist span calculator. 2x8 Spruce #2 joist at 16"OC with a deflection of L/360 have a maximum span of 13.5'.

My question is, considering the knee walls being in the middle of the joists, will 2x8's be enough?

Thank you.

09-21-2009, 04:47 PM   #2
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1. A spruce 2x8, 16"o.c. will carry 40# live load and 10# dead load and span max. 11'7"

2. Spruce 2x6, 16"o.c' span 12.5' will carry 403# Spruce 2x8, 16"o.c. span 12.5' will carry 702#
403 + 702 = 1105# / 12.5= 88.4# per lin. ft. / 16" = 66.5# per square foot if no holes in middle 1/3 of joists.
3 How much headroom do you have to the collar ties?
4. Where are the collar ties located from the peak outwards horizontally?
Be safe, Gary

 09-21-2009, 05:39 PM #3 Newbie   Join Date: Sep 2009 Posts: 3 Rewards Points: 10 Thanks for your reply Gary. I have just over 7.5 feet to the collar ties. They are 22" below the peak of the roof and measure 6 feet long. So are you saying that 2x8's should be enough?

 09-21-2009, 07:06 PM #5 Newbie   Join Date: Sep 2009 Posts: 3 Rewards Points: 10 Good info, thanks again.

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