Steel strapping in lieu of bridging joists?
CDNReno
| Posted in General Questions on
In renovating my 100 year old house I am trying to strengthen the somewhat bouncy floors. 2×8 spanning 14 feet and 2×6 spanning 13ft, etc. We have sistered some joists already.
In the places where possible I am installing solid blocking/bridging. However there are plenty of joist bays where ducting make it impossible to do to any type of solid block or even cross bracing.
Would running some Simpson straps on the bottom of joists add anything? Obviously they’re going to be less useful than proper bridging, but wondering if it’s worth doing at all. There seems to be disagreement online (as usual).
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Replies
CDN reno,
Bridging or blocking has two functions. It helps the joists resist twisting, and it helps them share loads. Steel strapping on the underside will aid with the first, but not the second. To do that the strapping needs depth, so either a steel T profile or 2"x lumber.
The simpson ltb system works well but it ties top to bottom and vice versa on neighboring floor joist. This transfers the downward force to the top of the adjoining floor joist, reducing sag and bounce. But a strap along the bottom will not help with that. This is also how blocking and x brace wood works( though instead of tension, they are mostly resisting compression) , the Simpson system is easier to visualize the forces involved though.
Edit, this was meant to answer op, not Malcolm, sorry Malcolm.
freyr_design,
Here I was enjoying a beautiful sunny day. Truck got towed to the shop this morning so can't do any work even if I wanted to - and then you go and reply in the wrong place. Unforgivable!
Ha! I’ll do better…
This does look like a good system though it seems like the LTB would be for new construction and the NCA would be for a retrofit option.
Other than speed is there any specific advantage of a Simpson cross bracing vs. solid blocking?
Yes the NCA system is in compression rather than tension obviously (from the name). I tend to trust steel in tension more than compression as that’s where its biggest strength is, but I’m sure that system works well enough. The ltb system is very strong and makes the floor much stiffer. I would argue maybe even more than blocking as the connections of nail-steel-wood seems stiffer than nail-wood-wood.
Thanks. I think I'll block what I can and strap the rest just for the twisting.
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Throwing some Simpson straps on the bottom of the joists could help a bit with the bounciness issue, but it won't work miracles like solid blocking or proper bridging would. It's kind of a compromise if you're stuck because of ducting. Some improvement is better than nothing, but don't expect it to solve everything.
Uiloco,
Yeah, straps lengthwise along the bottom of the joists help in theory, but the tests show they don't do much in practice because of the problem of fastening them to the wood tight enough to resist deflection. The problem is similar to adding a 2"x4" bottom flange to floor joists. Even with glue it's difficult to get a good enough bond to stop them creeping.
I've found the 2x4 sistering on the against the bottom side of the joist to work well for de-bounce especially if done on both sides. Subjective, about the same as sistering a full size joist. Needs to be glued and nailed. Essentially you are making a partial I-joist.
Where it doesn't work is taking any sag out of the joists. The only way to do that is by sistering and laying new subfloor over the new flat joist.