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Old 04-10-2019, 09:41 PM   #1
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joist sister question


I need help, please. I want to add a bedroom in my attic. It currently has what appear to be 100 year old yellow pine 6" ceiling joists 16" oc.

The house has a center hall that runs gable end to gable end. The joists span 14 feet from each side and rest on either side of the hall. (Have I said that clearly?)

Would an 8" #2 common sister be adequate? New place, new inspector, don't want him to think I'm stupid too soon.
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Old 04-10-2019, 10:07 PM   #2
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Re: joist sister question


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Originally Posted by Debbie Doright View Post
I need help, please. I want to add a bedroom in my attic. It currently has what appear to be 100 year old yellow pine 6" ceiling joists 16" oc.

The house has a center hall that runs gable end to gable end. The joists span 14 feet from each side and rest on either side of the hall. (Have I said that clearly?)

Would an 8" #2 common sister be adequate? New place, new inspector, don't want him to think I'm stupid too soon.

Where I live a floor joist is 2x10 so I will let others comment on the 2x8.


Usually only one outlet is a bearing wall with support right down to the ground, so would that make the span on one side greater than 14 ft?
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Old 04-10-2019, 11:13 PM   #3
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I think the deal is that a 2X8 glued and nailed to the existing 2X6 gives you something approaching a 2X10.

. And oddly, both sides of the hall sit on footers. So I think the span is right.

It's almost like they expected someone might add an upstairs addition. The hall is about the only place you could put stairs.
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Old 04-10-2019, 11:19 PM   #4
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Re: joist sister question


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Originally Posted by Debbie Doright View Post
I think the deal is that a 2X8 glued and nailed to the existing 2X6 gives you something approaching a 2X10.

. And oddly, both sides of the hall sit on footers. So I think the span is right.

It's almost like they expected someone might add an upstairs addition. The hall is about the only place you could put stairs.

Sounds good but stairs tend to block a hallway, can you make that work.
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Old 04-11-2019, 12:09 AM   #5
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Lol yeah, they do. If I can figure it all out and do it, the only room that would be blocked is a bedroom that I'll make a closet and en suite.

It will be accessed through the master. And under the stairs will make a tidy spot for an air handler.
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Old 04-11-2019, 12:49 AM   #6
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Re: joist sister question


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Originally Posted by Debbie Doright View Post
Lol yeah, they do. If I can figure it all out and do it, the only room that would be blocked is a bedroom that I'll make a closet and en suite.

It will be accessed through the master. And under the stairs will make a tidy spot for an air handler.

I would say you have a plan under way, after you have done the joist work add 2x4 blocking between the joists at the 7 foot mark.
If you are building a nee wall at on the edge of the floor you want solid 2x8 blocks under the far edge of the floor and seal around those blocks.
No air leaks from warm house to insulated space. While you are at it keep an I out for any gaps from down stairs into insulated space, they need to be air sealed.
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Old 04-11-2019, 04:53 AM   #7
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Great points, thanks.
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Old 04-11-2019, 08:37 AM   #8
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Re: joist sister question


There's always the option of retracting stairs.

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