Worried about weight on 2x8 floor joists - AVS Forum
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post #1 of 17 Old 06-16-2014, 05:55 AM - Thread Starter
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Worried about weight on 2x8 floor joists

I'm about to do the subfloor above me with double drywall which is 12.5mm soundbloc type and green glue and also the ceiling with the same but i'm not sure the floor joist can take all that weight ?

The joists span is 11' 5" and are spaced 24".

This needs to be safe as i have a new born baby in the room below

Any advice would be great thanks

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post #2 of 17 Old 06-16-2014, 10:08 AM
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Is this framing just carrying a ceiling load or is there a room above?

If its just a ceiling that should be fine, if there is a room above you may want to consider beefing up the construction
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post #3 of 17 Old 06-16-2014, 11:28 AM - Thread Starter
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Originally Posted by bluewaves View Post
Is this framing just carrying a ceiling load or is there a room above?

If its just a ceiling that should be fine, if there is a room above you may want to consider beefing up the construction
Yes there is a room above,what about if i use less drywall ?
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post #4 of 17 Old 06-16-2014, 11:49 AM
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I know where I live 2x8's on 24" centers for a 12' or so span used to be allowed in the past but it not longer meets minimum code, The drywall isn't the issue, its going to be the active load on the floor above, the floor is going to be super bouncy and will end up sagging over time.

Me personally I would beef up the framing, adding additional joists and going to 12" center would be my choice, or sistering the existing joists.

Are you sure they are 2x8's and not 2x10's? or possibly some form of engineered joist?
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post #5 of 17 Old 06-16-2014, 12:08 PM - Thread Starter
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Quote:
Originally Posted by bluewaves View Post
I know where I live 2x8's on 24" centers for a 12' or so span used to be allowed in the past but it not longer meets minimum code, The drywall isn't the issue, its going to be the active load on the floor above, the floor is going to be super bouncy and will end up sagging over time.

Me personally I would beef up the framing, adding additional joists and going to 12" center would be my choice, or sistering the existing joists.



Are you sure they are 2x8's and not 2x10's? or possibly some form of engineered joist?
This was built in the 1930's i live in England by the way,i've check and yes they really are 2x8 joists.

Seems like i can't bloody win,it's one thing after another

Add to that upstairs don't even have subflooring down so i have no idea how i'm going to green glue with dd the underside as i've read from ted that it needs to be screwed in

Last edited by Antony1987; 06-16-2014 at 12:14 PM.
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post #6 of 17 Old 06-16-2014, 01:46 PM
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Can you double them up ? That should be easy to do and low cost.

If they are open and exposed but another one right next to each existing to strengthen them up. They are weakest at the center point so adding a second one would probably increase the total strength and give you more peace of mind. I'd use something like heavy duty construction adhesive and some framing spikes. Spread the adhesive well and apply it heavy. Once the adhesive dries it's all over, it's there forever. That's probably the easiest thing to do.

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post #7 of 17 Old 06-17-2014, 03:46 AM
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It's called sistering.


I would add a 2x8 (@ 1.5" x 7.5" to the 2x8 and some joist to joist blocking, to stiffen the floor.
Construction adhesive with a nailing pattern. You might get away with sistering every second joist.


Is that old floor level?
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post #8 of 17 Old 06-17-2014, 04:17 AM
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If the flooring is at all bowed, I'd sister with 2x10s.

Here's one article about options:
http://www.thisoldhouse.com/toh/arti...1111-2,00.html

You can find a bunch of articles about this. You can run into a lot of problems, though, such as if a lot of wiring runs through the joists.

By the way, can I get rid of "active topics" that showing up on the right side of the screen? It's annoying.

Bob
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post #9 of 17 Old 06-17-2014, 04:21 AM
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+1, sistering, if the floor is sagging you could consider jacking them up as you sister, but you need to determine if that will cause havoc with the 80+ year old structure above.
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post #10 of 17 Old 06-18-2014, 03:57 AM - Thread Starter
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I've made a mistake the joists are 3x6,i won't be putting anything on them and will now put a new lowered ceiling with new joists etc.

The room span is 11'5" would 2x6 be enough to safely take the weight of double 12.5mm soundbloc with green glue and 100mm of insulation ? Or could i get away with using 2x4 ?
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post #11 of 17 Old 06-18-2014, 04:57 AM
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You can play around with this calculator. depending on choice of wood for the 2x6s and spacing you can span your room. Dead load is the weight of the ceiling structure. I would not use 2x4s.

http://www.awc.org/calculators/span/...al+Span#answer
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post #12 of 17 Old 06-18-2014, 05:04 AM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post
You can play around with this calculator. depending on choice of wood for the 2x6s and spacing you can span your room. Dead load is the weight of the ceiling structure. I would not use 2x4s.

http://www.awc.org/calculators/span/...al+Span#answer
Thanks for that link,could i still use the green glue i bought to do the underside of the floor with a thin type plywood or would it not be worth it ?
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post #13 of 17 Old 06-18-2014, 05:08 AM
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Adding damped mass underneath your floor boards will take part of the edge off the foot fall sounds. Not sure I would use plywood. Drywall is the material of choice. You should have plenty of clearance to use drywall.

Last edited by BIGmouthinDC; 06-18-2014 at 05:23 AM.
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post #14 of 17 Old 06-18-2014, 05:40 AM - Thread Starter
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Originally Posted by BIGmouthinDC View Post
Adding damped mass underneath your floor boards will take part of the edge off the foot fall sounds. Not sure I would use plywood. Drywall is the material of choice. You should have plenty of clearance to use drywall.
So would i be ok with just one layer of 12.5mm soundbloc drywall which weighs around 70lb per 4x8 sheet with green glue on the underside of the flooring with 3x6 joists ? I'm just worried about it all failing
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post #15 of 17 Old 06-18-2014, 06:47 AM - Thread Starter
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The joists size are 75mm x 160mm,the room span is 11'5" what can i safely do ?

Any advice would be great ?
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post #16 of 17 Old 06-18-2014, 07:42 AM
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So you are talking about the equiv weight of 3 or so people standing in the room above.
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post #17 of 17 Old 06-18-2014, 12:44 PM - Thread Starter
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Originally Posted by BIGmouthinDC View Post
So you are talking about the equiv weight of 3 or so people standing in the room above.
Depends on the size of the people

I just want to know if it will fail or what ? I just want to get this green glue up and see what difference it makes,i'm sick of hearing stomping and talking from above,i know what everyone in this thread has said to do is the right thing but i've just lost my job and really need to get this up so what could i do with what i have and a very small budget
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