Metal Bridging vs. Wood Blocking
Is there an opinion about about metal bridging vs. wood blocking for floor joists? I have a near 10′ run of 2×8 floor joists that I intend to insulate between with mineral wool. Would the metal bridging be better for getting the batts closer to each other or is it inferior for some other performance reason? I do not plan on running, wires, duct, or pipe in the joist bays.
From what I can tell, metal bridging is about 30% cheaper for materials than blocking.
I’ve read where the metal bridging becomes tighter as the wood dries out but that wood blocking becomes loose in the cavity as things dry out and can cause squeaks.
Is 10′ too short to be using ridging/blocking? Are the benefits worth installing it?
Peter
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Replies
Peter,
If your insulation is carefully installed to minimize voids, I don't think you'll see a significant performance difference between floor assemblies that use bridging and floor assemblies that use blocking.
You may be interested in a Q&A from Fine Homebuilding. Here is the link: "Bridging options."
Here's the answer from that column:
"Chris DeBlois, a structural engineer with Palmer Engineering of Chamblee, Georgia, replies: ... I don’t know of any research that has drawn hard and fast conclusions on the various methods of bridging and blocking. But even if such research has been done, I doubt the results would make the headlines because I don’t think there is much difference between the types of bridging. From a structural perspective, you are correct: Solid blocking and metal (or wood) X-type bridging do accomplish the same task.
"The blocking or bridging between joists (or rafters) also contributes to this phenomenon. For example, with bridging installed between joists, a piano leg sitting over one 2×10 is actually supported by several. The weight of the piano is centered over a single joist, but the bridging transfers some of the weight to the adjacent joists. So the floor deflection under the piano leg is much less if four or five joists are bridged together to share the load than if bridging has been left out and one joist has to carry the whole load.
"But what’s the best bridging system? If properly installed, solid blocking, any style of metal X-type bridging and wood X-type bridging again are equivalent in my book. The choice comes down to the details you described: which system is easiest to install, squeaks the least and holds up the longest.
"I think 1×4 X-type bridging is the best option for a number of reasons. First, it’s a little less demanding to install this bridging adequately. If a piece is slightly short, it can be attached a little higher up from the bottom of the joist and still do its job just fine. On the other hand, solid blocking should be cut precisely to length and is less effective if the nails have to bridge a gap between the bridging and the joist.
"Another drawback to using solid blocking is that it sometimes creates a hump in the floor if the blocking and the joists shrink at different rates. X-type bridging does not suffer from this problem.
"Finally, X-type bridging interferes less with wiring and plumbing systems than solid blocking does. Too often, pieces of solid blocking are removed and not replaced by plumbers and electricians. X-type bridging is less likely to be taken out in the first place, and if it is removed, it’s much easier to replace around the wiring or the pipes than solid blocking is.
"The bottom line is that any of these systems installed properly will work just fine. The final choice is based more on personal preference than proven superiority."
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