Bouncy floor support advice please.


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Old 03-13-23, 06:51 AM
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Bouncy floor support advice please.

Hi all,
We recently bought a fixer upper and although the inspector told us one room of the home should probably have a support/brace due to a bouncy floor, we noticed that the living room which is 34ft x 13ft bounces also, this has me worried so although i am not looking forward to the crawl space i feel i need to do something.
the current beams run the width, and they are 8x2's. there is no load above them, just the open living room. so i hope someone could help or advise on my plan.
1st would i be right in thinking i HAVE to dig 2x2x2 holes to add hardcore then concrete to put the cinder blocks on to support the new support beam? as i have to run the whole 34 ft, would 8x2's be ok? or should i screw 2 together? so 8x4? is this acceptable or overkill? i did plan on the cinder pillars being 6ft apart.
sorry if this is abit random or silly, my brain is currently fried from all the things we ( not the inspector ) have found.
thank you.
 

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03-13-23, 09:31 AM
Pilot Dane
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You probably will do solid wood blocking. Installing each bay's block offset allows you to nail straight into the end. It is important that the ends of the blocks are cut square and fit snug in the joist bay. They work by transferring the load to adjacent joists and can do a lot to limit flexing and bouncing.

 
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Old 03-13-23, 07:22 AM
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If your "2x8 floor joists" span 13 feet, the first thing I would check is whether or not you have solid blocking at mid span. Blocking is a tight fitting block, perpendicular to and fastened between your joists. It's best if the block would also be 2x8, but if you have bays with ductwork or something in the way, you can lay those flat under the obstruction.

Once that is installed, see if it is stiff enough. The blocking acts to help transfer weight from one joist to the adjacent ones by preventing deflection (lateral movement) of single joists. The floor acts more as a unit when blocking is installed, without it the joists bend more.
 
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Old 03-13-23, 07:25 AM
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Do you actually need a beam? You might be able to sister the existing joists. That would save the trouble of a beam & footers though it can sometimes be a difficult job depending on how many facilities (electrical, water, HVAC...) are running through the area blocking access.

If you need to add a beam that definetely puts you into the territory of a building permit and inspections. Your codes will specify what size and type of footers would be needed for a beam.
 
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Old 03-13-23, 07:31 AM
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There is no blocking midspan bar one area that had a wood burning stove that they build 2 pillars underneath. the bounce isnt huge but my wife and i were goofing around and noticed there was some flex.
there is very little in the way, only one outside faucet line and the Hvac electrical cable. ( all ducting is in the attic )

below is a photo, sorry it would not let me do it from my phone earlier.
 

Last edited by PJmax; 03-21-23 at 01:08 PM. Reason: resized/enhanced pic
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Old 03-13-23, 08:42 AM
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Add blocking down the middle, then reassess.
 
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Old 03-13-23, 08:54 AM
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Do you mean add block pillars and no wooden beam?
 
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Old 03-13-23, 09:04 AM
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Ive had floors with same bouncy feeling even with blocking.

I ended up installed small Glue/lam/LVL's perpendicular to the joists with adjustable posts right on the cement floor with excellent results.

That install does not require engineering or permits, it's not load bearing, it's just not allowing the joists to deflect.

Start with the easy first.
 
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Old 03-13-23, 09:05 AM
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I described what blocking is and what you should do in post 2.
 
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Old 03-13-23, 09:23 AM
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Sorry it took me several reads for it to sink in.

I have to go back under for plumbing woes later so I will have a look incase there is any blocking.
 
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Old 03-13-23, 09:31 AM
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You probably will do solid wood blocking. Installing each bay's block offset allows you to nail straight into the end. It is important that the ends of the blocks are cut square and fit snug in the joist bay. They work by transferring the load to adjacent joists and can do a lot to limit flexing and bouncing.

 
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Old 03-14-23, 07:53 AM
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Small update, upon actually going back in it seems the beams actual measurement is 9.5 inches x 1.75 inches ( only the very 1st beam was 8x2.... ) i measured 6 and they look to be all the same moving further along.
they also have what i only guess as a earlier kind of blocking, which is in the shape of a X. should i remove these, or more likely add as recommended above? or go direct to digging footings and a supporting beam?
 
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Old 03-14-23, 08:35 AM
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It sounds like you have 2x10 floor joists.

You already have blocking. Removing the cross bracing to replace with solid blocks will have little to no affect. If you sister the joists the bracing will need to be removed.

With a nice, clean crawlspace and few systems in the way, I'd sister the joists. If you want to keep the cost down you can start by doing every other joist in the problem areas. Then you can add more if needed.

You could also add a mid span beam but I'd consider it a distant second behind sistering the existing joists. Done properly this would require a permit and inspections since you'd pour concrete footers and install a properly sized beam. On the down low you might shovel a flat spot on the ground and use concrete paver blocks then posts up to your beams. The proper method is very reliable though a lot more work and expense. The cheap method can work well if done properly but if done improperly it could be useless so there is risk especially if you've never done it before.
 
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