Old house floor question...
 

As you may know, my house is 115 years old...and has been showing it's age a bit more recently. Anyway, the floors have had a bounce to them since moving it. I checked the old blocking between the joists, and have found them to be a weak design...1X4, cut at an angle and installed diagonally. What my dad and grandpa did to old houses like this was to block it with 2X4, cut straight. They did that to an old house for my brother, and it seemed to work very well...so that's going to be my first task.

Now, if blocking doesn't work, I have the option of a floor screw jack. I can place one in the center of the floor in the basement, tighten it up, then box it in and forget it. What my question is...What sized beam should I use to span the floor, perpendicular to the joists, to rest between the jack and the joists? Would 4X4 work, or should I go with a bit more heft, and wrestle a 6X6 down there?

I'm hoping that blocking fixes my concern for now...more time consuming, but I won't be wrestling beam around and in between the stairs and chimney base.

With just one centralized horizontal support for the beam, I have a sense that the overall length of the beam might have an influence on the answer.

I had a bouncy floor in my house. If you want to stiffen it you need a full depth block...In other words, if your floor has 2x10s the blocking needs to be 2 x 10. Diagonal cut bridging is good but the attachments might have gone weak on you.

At my house we cut the blocking and screwed it in with about three toenail screws each side. I believe we glued it too. Made a big difference. It has to go all the way to the wall. In this way it forms a beam. It could also be done twice spaced out in even distances.

Do you have enough height to give up for a beam set below?

I actually think the X blocking is the way to go. They just need to be fastened good, and the two pieces need to be close together, like touching. These transfer any lateral force to the neighboring joist at the opposite end, and the two work together to keep the joist from twisting.

I have 6' clearance in the basement, and have to duck or hit the ducts for the furnace. I'd like to avoid a beam, if at all possible, due to the post getting in the way in the middle of the floor. But, if I must, then I must. I can get away with it more under the living room, since it's only storage and the furnace there. My wood shop is under the dining room, and if I were to put a beam in the middle of the floor there, it would completely block me from being able to have my tools and bench there.

I'll measure the joists...I believe they are 10". Would I be able to stagger them and still create the solid beam feel? I plan on screwing everything in place due to lack of space for a good hammer swing.


It currently is X blocked, and it's a wreck. More than half of them are loose, and 3 or 4 have completely come unattached from one joist.

Since the boy child has to work all weekend, and girl child broke up with her boyfriend, I'm going to have to pull this off with the help of my wife only.


I've got a few more projects to get done before Winter shows up. It's a never ending job with this old house. I've got cracked window panes to replace, and a wooden storm door that needs the bottom trimmed off so it can shut properly. I've also got to add a short piece of ductwork, insulation and a front face into the box I made to sit the refrigerator on so I could get it out of the tiny kitchen.

I do what I can...which doesn't ever seem to be enough. :)

If it doesn't cost too much, that is not too many joists, I'd almost take out the existing X bracing and sister a same sized joist to each existing one. I suspect getting them on top of each wall at the ends would be impossible. Would need to do that on one end and fasten something solid to the wall under the other end of the joist. Use polyurethane adhesive and 3 inch screws between the old and new joist and then put in new X bracing. That would avoid a block under them and the attendant head banging.

Would even be good if you found joists with a small crown and put the convex side up, (of course).

Upon re-reading of the OP, I may have got it wrong. Somehow I thought you were talking about the largest room having some bounce. Sistering joist for the whole house would be a tall order.

One thing that might be superior to X bracing is using blocks of the same stock of the joists, say 2x10 and just fill the space completey. Probably a tad more firm than the X bracing and should last longer.

Since you already have them I might start by jacking up the floor as much as you can and reattaching what you have. Doing the solid blocks is a fair amount of work and you must cut them so they are a very tight fit.

Staggering them enough to end screw will be ok too, but keep them as close to lining up as you can.

Double checked size...2X8. Sandwiching joists is more than I can handle...115 year old house on limestone foundation. Each one would have to be cut specific for it's spot due to nominal dimension lumber differences in 115 years.

I"m going to block brace each one and see how it goes.

As for largest room having bounce...both living and dining rooms are the same size, separated by a stone chimney. Both have some bounce.

Like I said, I'll try staggered blocking, keeping every other in line, then offset the opposing ones by a board's width, giving me room to screw everything together without having to resort to toe nailing the boards in.

The rooms are longer than they are wide, and the joists run across the width, not the length...the strongest possible at the time of construction. After this job is done, the dining room will wind up being sanded and refinished. It's currently under carpet, which was a mistake, IMHO.

I've only recently fallen into a few bucks, and every dollar is going into the house. My only issue is physically being able to get it all done. Time to call in some paybacks for favors from the past...

Quick question...should I do this with pressure treated 2X8? Moisture isn't much of an issue, other than basic humidity.

No, I wouldn't. Its not wet is it?

If the other rooms don't bounce it makes me wonder if some of your joists are damaged by cutting by the hvac guy or termites. I'd take a close look and replace anything that is compromised before moving ahead with the blocking. The blocking depends on the integrity of the blocked joists for its integrity.

PM me if this doesn't make sense.

No, it makes sense. It's dry, and the wood has no termite or rot issues shown. It's just old...very, very old. The bouncing floors have not created an issue, just more of an annoyance. None of the joists have been cut away for HVAC or anything else. The cross braces have loosened up from years of expansion and contraction.

Since I can use non-pressure treated, it's going to be a few bucks cheaper. That's great to hear.

the pressure treated would not be as good given its moisture content it would twist and shrink more.

If there were water issues they would take precedence over the bounce.

Good luck with it Jon!

Pressure treated lumber tends to be slightly lower quality than reg. old doug fir in my experience as well.

Cutting solid blocks can indeed be a pain. The spaces are rarely perfect squares/rectangles in older houses or new houses for that matter. But even if the cut isn't perfect, can be made to work. Get a big box of cedar shims and jam those into any gaps at the corners with some construction adhesive. Just relying on the pressure fit to hold them forever can fail now and then.

2x8 could be a lot of the problem. I think that's often the minimum amount code will allow. It's a bit of a drag, but a few posts in the basement might be the most certain. Doesn't need to be jacks. You can use a jack to lift it an eighth or so and slip a post under, with a piece of treated at the bottom on the concrete. If you do go with a beam, I would think a 4x6 would give major support.

They are likely a full 2" x 8" or more being 130 years old. They should be plenty strong unless compromised by damage.

I understand the reluctance to add posts in areas you are using daily.