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Old 06-13-2013, 05:45 PM   #1
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Remodeling attic: ceiling joists -> floor joists


Hi all,

I'm in the daydreaming stage of building a home theater. Each day I go up in the attic and pretend to place things and try to get a better understanding of how my house is built, etc. I believe I'm fortunate in that I have a huge attic that seems to be mostly wide open. My house is approx 2500 sq feet, it's one story. Attic access is from the garage (would change pull down stairs to a real staircase.) House constructed in 2006-2007.

So, the first part that I want to tackle is building a large empty floor. I am a bit troubled on the best way to build a floor in my attic space. I've attached two photos to this post. The first is an unadulterated view of the attic, the second has some highlighted points of interest.

Down the middle of this area is a massive laminated support beam. It's like 12" tall, 4" (nominal) wide, and it runs the length of the "main room" in the house. It is supported on one end by a wall that is part of the kitchen, and on the other end by a bedroom wall. It also is where 4 roof supports attach (#'ed in the picture.) Also, this beam splits this big space up because it's 6-10 inches higher than the rest of the floor in this area.

(Also in this picture is the "floor" on either side of the beam, which is 2x6s which are supported on one side by a wall, and on the other side nailed into the beam. They span about 10 feet (which is about max for a 2x6 as a ceiling joist), which makes this whole area about 20 feet wide or so. The AC compressor line is also highlighted just to note that it would be covered up. Also, there is an AC duct to the living room pictured, because that would need to be dealt with. The rest of the AC ducts I could reroute through the "rafters" around the room and have them get to their destination without issue. The chimney exhaust frame dictates the back of the room.)

So, my question is what is the best way to build a floor out of this space? The obvious big problem is the 12" tall beam that sticks up in the middle of the room, so the rest of the floor has to be "brought up" to that level. I've thought of two way to do this.

1. I would install a header board on the left side of the picture, right where the "E" in "Existing floor profile" is, and then a header along the side of the support beam, and then span that area with 2x8s 16" on center. I would then do the same on the opposite side of the support beam. This would give me a giant level floor supported by three load bearing structures (the wall on the left side of the picture, the support beam in the middle, and a wall on the right side of the picture (not highlighted, but it's an exterior wall.) Being 2x8's 16" on center, with spans of about 10 feet, this should be plenty strong enough. Although I could do 2x10s just to be safe.

The potential problem with this is that it would mean I'd have to reroute some of the AC ducts, which means patching the ceiling in my living room and trying to match textures, etc.

Or,

2. I could sister 2x8s to the existing "ceiling beam/joist" 2x6s, which would make them strong enough to be considered floor joists. I still would need to raise the floor high enough to make it all level with the support beam in the middle. So I was thinking I could then take some 2x6s and run them perpendicular to the sistered 2x6/2x8s, and the new 2x6s would add just enough height to be slightly above the center support beam. I don't know how close the 2x6s would be because they wouldn't really be spanning anything, so probably 24" on center would be plenty enough.

The problem with this method is that it adds a lot of weight onto those sistered 2x6s/2x8s. The good thing is that since the top layer of 2x6s is running perpendicular to the original joists, I could then route my AC ducts perfectly fine and not have to start patching things and creating new troubles.

Anyway, I was hoping to get some input from some of you experts out there. Thank you kindly.
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Old 06-13-2013, 05:53 PM   #2
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Remodeling attic: ceiling joists -> floor joists


Going to need an engineer on this one to redesign the roof and flooring supports.
2 X 6's are undersize for floor joist.
It would be a big help to go back and add your location to your profile.
Just go to quick links to edit.
Looks like just 2 X 6's for roof rafters, that's not going to be enough room for baffles and insulation in most areas. Going to have to pad them ouT.
Also going to need a ridge vent and plenty of soffit vents.
No clue how your going to reroute those ducts unless you changed them to rectanguler solid insulated lines and ran them under the floors.

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Last edited by joecaption; 06-13-2013 at 05:56 PM.
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Old 06-13-2013, 06:16 PM   #3
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Remodeling attic: ceiling joists -> floor joists


I agree, you will need some design help---architect,designer or engineer--and a good HVAC company----even an experienced GC will no touch that without a set of plans---

So start your dream with a set of plans---Mike---
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Old 06-13-2013, 08:00 PM   #4
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Remodeling attic: ceiling joists -> floor joists


Hi there!

Thank you for the advice. I definitely will be consulting with a struct engineer. Do you have any idea what I should expect to pay for that?
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Old 06-13-2013, 08:11 PM   #5
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Remodeling attic: ceiling joists -> floor joists


Quote:
Originally Posted by chamino View Post
Hi all,

I'm in the daydreaming stage of building a home theater.

The first is an unadulterated view of the attic, the second has some highlighted points of interest.
.
I happen to be in total agreement with Joe and Mike.... BUT I'm just interested in what kind of movies you're going to be showing up there..
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Old 06-13-2013, 08:12 PM   #6
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Remodeling attic: ceiling joists -> floor joists


That's one taboo question on any DIY site.
Make some local calls and find out.
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Old 06-13-2013, 10:26 PM   #7
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Remodeling attic: ceiling joists -> floor joists


Joe, what is taboo---asking what kind of movies he's going to watch,or the cost of an architect?

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