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The subfloors in my new construction home are pretty squeaky and there is a good amount of deflection. I am looking at some simple DIY things that I can do hopefuly reduce the bounce and squeaks. Most of my basement ceiling is drywalled, but there are a few places where it is open.

The first thing I plan to try is to look for gaps between subfloor and the support system to shim in some pieces.

I also read about adding metal bridging. When looking at this article, I noticed I have a different type of joist system - open web floor trusses so I wanted to see if the same fix applies since I do not see any existing bridging. The article mentioned something about approval: Don’t add bridging to manufactured lumber like I-joists or truss joists until you consult an engineer or building inspector. and I am not sure if this applies to me or not? I also see a few places where they sistered some wood and those cracked. I'm not 100% on all the terms, so I don't want to google and use the wrong techniques. There is also a lot of board separation above the subfloor - I mention this in case it is also relevant.

Here are some photos, I would like to know recommendations and other techniques that may be appropriate for this area. I have a few areas where pipes run along the support system.

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  • For squeaks, shimming and/or using squeek-stopping screws may be sufficient. Bounciness may be harmless.
    – keshlam
    Feb 18 at 4:13

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No, do not add bridging between open web floor trusses. @Jasen is exactly correct.

Bridging, blocking, etc. does not add much strength for bending anyway. It would be better to add a bearing wall or reduce the span if possible. However, you can’t just add a bearing wall without having the manufacturer verify where it will need to be installed. Then, of course , you’ll need a footing, etc.

Open web trusses are designed so that the top chord is in compression ONLY, the bottom chord is in tension ONLY and the diagonal chords are either in tension or compression ONLY.

When additional blocking, bridging, etc. is added, it allows forces to be transferred from truss to truss. This action is called “double bending”. That is to say one of the chords could be in tension and the additional bridging could cause the chord to be in bending...tension and compression. That additional tension could exceed the allowable stress of the member or the connector.

You have open web trusses not I-joists, but the effect is similar. The additional bridging, etc. could transfer additional loads that exceed the web strength, chord strength, or the glue strength between the web and chords.

You’ll need to consult the truss manufacturer to see where additional bridging, etc. can be added. (I doubt a structural engineer will assist you because they didn’t design the connectors. )

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  • Thanks. I'll try to find the manufacturer, would that be on the wood somewhere? Builder is never very responsive with any details like this. I also read this: openjoisttriforce.com/… I see very few boards going across - i think the one i see is a strongback - could I add more strongbacks on my own? Or is this another thing which needs to be calculated and added in specific ways?
    – HelpEric
    Aug 30, 2020 at 18:02
  • @HelpEric Strongbacks and perpendicular bracing is often required to keep the trusses exactly vertical. With heavy loads or long spans, the trusses will tend to layover on its side. I doubt if you have this condition. I’d ask the builder where they were purchased and then ask them if you can add another support wall...but remember, you’ll need a footing too. I’d make a quick sketch of the trusses with all the dimensions, including spacing between each diagonal connector. (Are all the spacings equal from end to end?)
    – Lee Sam
    Aug 30, 2020 at 19:17
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consult the engineer.

the bridging transfers loads on the top of the joist to the bottom of the adjacent joists. if the joists are solid lumber this is not a problem, but if they are wooden I beams, the loads could cause the bottom chord to separate from the web. and on trusses could cause the bottom rail to bend

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https://www.youtube.com/watch?v=y1UOV1xROn0

On open web trusses this is a good solution if you can get a good measure on the weight needing to be supported. If its simply a load deflection issue you can do a single truss and test the new deflection. By unloading a truss via jacking it up top and bottom cord simultaneously, gluing and screwing the steel bars to both sides of each unloaded cord and then letting the glue dry fully before letting the load back on you can easily strengthen open web trusses. I am doing this right now to fix a few of mine due to an overloaded truss. Just remember, this is a single attempt repair, so do the math or oversize the thickness of the steel. And make sure the glue is fully dry before loading the truss. I am using gorilla urethane glue on mine. For really heavy loads cold pressed A36 is better than hot rolled A36 but cold comes in shorter lengths which may increase the number of joints. Full heliarc or tig welding and scab plates on each joint, drill a screw hole every foot and start screwing from the center out when applying the steel to the truss. Unlike the video I also added steel on my uprights but only press fit and glue, no welding to further limit my deflection under the one heavy load wall. I used 3/8"x3" thick hot rolled A36 steel on that and 5/16"x2" on the other trusses.

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