adding blocking between joists

[Bill Dufour]

My house built in 1969 has 4x6 floor joists spaced four feet on center. Then 2x6 tongue and groove planks at right angles. I am going to be working on replacing some of the galvanized water pipes in the crawl space. To add support hangers for the pex tubing I would like to add some blocking between the joists at a few places. This will help prevent rollover of the joists in a quake as well.
So should I push the blocking all the way up to the underside of the floor or leave a slight gap? I worry pushing it dead tight may lead to squeaks as the new wood dries. I know I could use plumbers tape and one inch screws but as long as I am down there I would like to add some amount of blocking.
Bill D

[Bruce Wrenn]

Why not use 1X4 strapping fastened to bottom of joist instead? No cutting, or fitting, and ends can bypass each other.

[Cameron Wood]

I'm guessing that floor is a bit bouncy. No need to leave a gap. Squeaks are mostly from subfloor moving up and down on nails face nailed from above.

[Bill Dufour]

Why not use 1X4 strapping fastened to bottom of joist instead? No cutting, or fitting, and ends can bypass each other.
Because I want to add the blocking to prevent roll over of the joists. Strapping does nothing to prevent roll over. X bracing would prevent roll over but it seems like blocking is easier to retrofit.
Bill D

[Scott Winners]

Hey Bill. I would do whatever Tom King says. My inclination would be to leave a small gap, but I think Tom's extensive old building experience is probably more valuable than my limited earthquake experience.

Also, if you got any visible sag in the floor above, getting all your blocking flush and gapless is probably not a realistic goal.

[Lee Schierer]

Because I want to add the blocking to prevent roll over of the joists. Strapping does nothing to prevent roll over. X bracing would prevent roll over but it seems like blocking is easier to retrofit.
Bill D

With 4 x 6 joists with a bunch of 2 x 6's attached to the top, why would the joist want to roll over? Blocking is generally used to eliminate floor bounce by making several joists work in tandem to support the load. I don't think an earthquake is going to roll them either. I think the foundation, walks and attachment of the rim joists to the foundation will fail first.

[Tom M King]

I don't think solid blocking is going to do much for the floor unless it absolutely needs some help.

If the quake is strong enough to make the blocking do anything, I expect there will be more serious problems in other places. Use a 2x instead of a 1x if it makes you feel better about it, and bigger fasteners.

[Bill Dufour]

In fact the joists are running in a direction that is unlikely to see much acceleration side to side. That means roll over is unlikely. Still as long as I am needing some strapping I might as well upgrade to blocking. Probably time is better spent shear tying the joists to the mudsill. I was surprised to find there is no code for foundation piers to be firmly attached to the joists.
Nothing will be done to tie the walls and roof down anyway.
Bill D

[Edward Weber]

My house built in 1969 has 4x6 floor joists spaced four feet on center. Then 2x6 tongue and groove planks at right angles.
Bill D

If this is your setup I would add blocking, essentially making a large torsion box.
The entire structure will become stiffer. I would not bother to leave a gap.
JMO

[John Pendery]

Did I read correctly that your floor joists are spaced four feet on center? Granted I’m in a very different part of the country, but I’ve never come across spans like that between joists, and I would imagine building codes would be much more strict out in your neck of the woods. It does remind me of a buddy of mine back when I did more framing. Whenever he was going to do something kind of sketchy he would call it going California. Maybe that’s why. Even with tongue and groove 2x6’s (which I assume serve as your subfloor?) running perpendicular to the joists I would imagine that floor would feel like a trampoline!

If you want to eliminate potential squeaks a bead of subfloor glue on the top edge of your 2x blocking would do the trick. For blocking to be effective it needs to be continuous as opposed to sporadically placed between joist cavities.

[Tom M King]

Blocking will be a big job. I wouldn't bet that any two spaces would require the same length block, and wonder how flat the faces of the joists are. If they aren't tight, they won't be worth the trouble. Too tight and they're hard to get in.

I remember back in the early '80's some friends of mine were putting blocking in like that under a old floor in a log cabin. Ross hit his thumb with a 28 oz. waffle faced Estwing. It sprayed blood, and he passed out. They had to drag him out from under the house.

I'd put a 2x from sill to sill under the joists and call it good.

[Bill Dufour]

I think people misunderstand the point of this blocking. I am not trying to reinforce the floor or stop sag. It is similar to fireblocking in walls in that is not really meant to add strength.
Bill D

[Lee Schierer]

Bill, I added blocking to the floor in our living and dining rooms. Tom is correct, every joist space was different. I used 4" long wood screws through the joists into each end of the blocking. I staggered each block enough to drive the screws into the new block. If I did it today, I would use timber lok screws and an impact driver. Some beeswax on the threads will make the driving go faster.

[Bill Dufour]

Lee I have pounds of 6" timber lock screws so I like your plan. With pex pipe things can weave back and forth across the staggers. Do impact drivers really have no kickback if the screw binds? My Hilti SDS+ will break my wrist if it gets hung up and I do not let go.
Bill D

[Ron Selzer]

Do impact drivers really have no kickback if the screw binds?

The DeWalt ones I have used have no kickback.
Ron

[Lee Schierer]

My Dewalt 20 volt brushless impact drives them with no problems. if it stalls it just stops.