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cibula11 12-09-2006 06:18 AM

Floor Joists in Attic
I am in the beginning stages of remodeling my unfinished attic for a nursery and small office. After starting to insulate I realized my floor joists we true 2x6's that spanned 20 feet at their widest point. The majority of the room, the span is 15 feet. The room is obviously a bit bouncy. Should I stop and fix this, or am I okay to continue? Suggestions. I have considered sistering the joists but I have heard this is pretty complicated. Also could add a beam below, but it would not be able to be in the middle of the 20 foot span, and of course the living room below is finished.

Daryl in Nanoose 12-09-2006 11:37 AM

So what would be the span if you put that beam in downstairs and what is the spacing of your 2x6 now? A few pics and or drawing would help us out here.

glennjanie 12-09-2006 11:54 AM

Welcome Cibula:
I would not recommend using the portion of the attic which spans 20' for anything but storage for Christmas decorations or empty boxes we save to send electronics back in (in case they fail in our lifetime). In portions of the attic where the span is not so long I would consider tying the joists to the rafters and perhaps even some sort of truss configuration from the attic wall line to outer perimeter of the house. Also, I would not drive any nails in the developing space; consider screws as fasteners instead, because the pounding of nails might cause ceiling cracks and nails to pop below. The spongey joists are going to make it hard enough on the celings below. The sistered joists are hardly ever a workable solution because they must rest on the outside walls to be effective; again screws would be in order rather than nails. I would not use the 20' span even if it were sistered with 2" X 12" joists; wood is just not that strong. The span should be broken up with ties to the rafters just to support the ceiling.
I do admire your effort to use space that already exists; some attics seem to be such a waste of enclosed space. I just think this job requires more engineering. Please post back and let us know how it turns out.

cibula11 12-09-2006 02:34 PM

The 2x6's are 16 o.c. If I were to put a beam in below. There would be one span of about 8 feet and another at 12. The house was once a one room school house that has been added on to. So, if I were to sister with 2x12, those joists would go from exterior to exterior (the old exterior, which is now the wall that seperates the new addition to the old).

Square Eye 12-10-2006 12:55 AM

My humble opinion..

The beam would be more effective and less trouble than sistering 2x12s in. When you start trying to sister in the joists, you will find that you will have to remove a portion of the roof and slide them in from outside. It is physically impossible to get a ceiling joist in the space from inside. You will get one end in a space, then the other end will hit the rafters and joists and will not make the turn to drop into place. Trust me on that :)LOL
Even at 12' span, the beam would be effective. The 2x6's though would be marginal for a 12' span in a living area.
But, houses built before 1970 often have true 2x6 floor/ceiling joists. It's been done before..:)
Make sure you provide adequate support under the ends of the beam. You will need at least 3 studs under each end and make sure the studs are sitting on a framing member under the floor. Bridging from the exterior wall to the next joist, or center it over a floor joist.

Anyway.. good luck!
Welcome to the forum!

Daryl in Nanoose 12-10-2006 06:38 AM

I agree with with tom 100%. Going with a beam below is going to be a lot less hastle.

cibula11 12-10-2006 11:39 AM

What should I use for the beam. In the past I have used 2 2x8's together. Would this be sufficient? If I could get away with something smaller that would be great. I just would rather not have a 12" beam breaking up my living room ceiling. Also, the distance of the beam would have to be around 15' (I haven't measured exactly). Can I buy lumber that long? So, to make sure this is what I am hearing from all of you, let me paraphrase. If I ran a beam from the gable end exterior wall to a wall in the middle of the room, I would give myself enough support? Thanks for the feedback, it all helps.

glennjanie 12-10-2006 11:53 AM

It is possible to strengthen a beam with steel plate sandwiched in between 2 wooden members with a bolt every foot staggered from top to bottom. You can visit a steel supplier and ask for the engineering department to tell you what to use. I'm betting it will take at least a 2 X 10 to bear the load; that is, a 9-1/4" X 3/8" steel plate between two 2 X 10s with the bolts and firm support on each end like Square Eye mentioned. Then, with the shorter spans in the attic, you can tie the 2 X 6s to the rafters above to help bear the load and make it pretty well.

Square Eye 12-10-2006 04:07 PM

You also might consider a steel I beam.
You can get more span, more load bearing capacity in a shorter, more narrow beam.
Wrap it/box it in, with 1x whatevers and forget it..
Be sure you have about 10 people who can help you set it though.
Steel gets very heavy very quickly!

Daryl in Nanoose 12-10-2006 06:44 PM

Alwright Tom, stop reading my mind.
ibula11 you may want to call a truss company and see if there is a Laminated beam they can make for this of course it would be thicker but maybe not as wide. Just a thought...

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