With those dimensions and the span, there should hardly be any load-bearing issues?
It also sounds strange that they would tip since it is significantly stiffer and more stable with 75 mm vs today's flimsy <45 mm joists.
The Swedish Forest Industries' guide specifies a span of 4.31 cm for 70x220 mm cc 60 cm C24. (Nailed, not glued, floor.)
It also sounds strange that they would tip since it is significantly stiffer and more stable with 75 mm vs today's flimsy <45 mm joists.
The Swedish Forest Industries' guide specifies a span of 4.31 cm for 70x220 mm cc 60 cm C24. (Nailed, not glued, floor.)
The sizing doesn't sound too wrong after all.
Despite this, 3 of the middle beams in the room have started to twist suspiciously like buckling over 30 years, and the parquet above is like a trampoline. I would guess that the twisting in the beams has caused the subfloor to lose contact with the beam underneath and that it's the subfloor that's flexing. Since they are solid wood beams, the beam can behave a bit more than modern glulam. It probably doesn't take many millimeters for it to feel shaky, does it?
As I said, I don't think the house will fall apart, but I'm more interested in how I can (re)gain the feeling of a firm floor on the middle level. In the areas where the ceiling in the basement is still intact, the floor feels significantly firmer to walk on, and the beams look straight and fine. That's the feeling I want back. One could imagine putting the ceiling back in the basement with the beams as they are, screwing the subfloor securely to the joists, and leveling/aligning from above? What do you think about that solution? The parquet likely needs to be relaid or replaced within a few years anyway.
Despite this, 3 of the middle beams in the room have started to twist suspiciously like buckling over 30 years, and the parquet above is like a trampoline. I would guess that the twisting in the beams has caused the subfloor to lose contact with the beam underneath and that it's the subfloor that's flexing. Since they are solid wood beams, the beam can behave a bit more than modern glulam. It probably doesn't take many millimeters for it to feel shaky, does it?
As I said, I don't think the house will fall apart, but I'm more interested in how I can (re)gain the feeling of a firm floor on the middle level. In the areas where the ceiling in the basement is still intact, the floor feels significantly firmer to walk on, and the beams look straight and fine. That's the feeling I want back. One could imagine putting the ceiling back in the basement with the beams as they are, screwing the subfloor securely to the joists, and leveling/aligning from above? What do you think about that solution? The parquet likely needs to be relaid or replaced within a few years anyway.
Perhaps the beams have twisted because it has been opened up so that the full swing in RH and temperature on the ground floor has reached the beams? Naturally, it hasn't improved by the fact that the stabilizing and stiffening effect of the ceiling has disappeared in the process, giving more freedom of movement to the beams.
It sounds a little strange that the subfloor wouldn't be properly attached to the beams, but it's not impossible. A phenomenon I've encountered at home is that our parquet floor sways in one spot. Since it is 14 mm thick and glued, it forms a semi-rigid "cake" on top of the subfloor. In our case, I'm convinced that the sway is due to the subfloor not being flat but sagging a bit there (floor chipboard on polystyrene on a concrete slab). It doesn't change over the seasons, so it doesn't seem to be caused by shrinkage/swelling.
Well, if your parquet floor has similar characteristics to ours, it might be that the tipping of the beams has caused the subfloor to go into waves, and the parquet is hovering over the low spots, springing when walked upon. (In our case, it's a big floor-standing speaker with a lamp on top that wobbles when we step in the sway, which is significantly more disturbing than the sway itself.)
However, we can only speculate about the causes. The only way to get a definitive answer is to open up and look, from underneath or above. If the floor is seriously annoying, it probably needs to be torn up to be fixed. Unless you can certainly tie the floor sway between the beams. Then maybe it can be fixed from underneath. Most likely, it needs to be opened both from below and above to be properly addressed. (Assuming the beams have twisted/tilted and the subfloor has followed along.) I don't think one should count on being able to shape the beams back to their original position/shape.
It sounds a little strange that the subfloor wouldn't be properly attached to the beams, but it's not impossible. A phenomenon I've encountered at home is that our parquet floor sways in one spot. Since it is 14 mm thick and glued, it forms a semi-rigid "cake" on top of the subfloor. In our case, I'm convinced that the sway is due to the subfloor not being flat but sagging a bit there (floor chipboard on polystyrene on a concrete slab). It doesn't change over the seasons, so it doesn't seem to be caused by shrinkage/swelling.
Well, if your parquet floor has similar characteristics to ours, it might be that the tipping of the beams has caused the subfloor to go into waves, and the parquet is hovering over the low spots, springing when walked upon. (In our case, it's a big floor-standing speaker with a lamp on top that wobbles when we step in the sway, which is significantly more disturbing than the sway itself.)
However, we can only speculate about the causes. The only way to get a definitive answer is to open up and look, from underneath or above. If the floor is seriously annoying, it probably needs to be torn up to be fixed. Unless you can certainly tie the floor sway between the beams. Then maybe it can be fixed from underneath. Most likely, it needs to be opened both from below and above to be properly addressed. (Assuming the beams have twisted/tilted and the subfloor has followed along.) I don't think one should count on being able to shape the beams back to their original position/shape.
The beam dimensions in relation to the span should be sufficient to avoid deflection issues, even with just nailed or screwed floorboards. If the floor joists sway (i.e., apart from the floorboards), they are likely moisture-damaged. However, I have more faith in the variants that @Oldboy discusses in post #19. I don't think it is possible to solve the problems without a thorough investigation.
I'm probably also leaning towards oldboy's perspective. Moisture in the middle floor is completely out of the question. The floor is open from below and bone dry.
It's also unthinkable that it's the parquet itself that is sagging. It's glued herringbone that's as old as the house, so the likely failure mode would be loose parquet pieces (which there are in some places). Possibly there's some type of board between the floor planks and parquet that could be sagging, but I haven't dug into that yet.
You're probably absolutely right that the best way to find out is to tear it up and start examining from above. The parquet is also nearing a renovation or replacement, but that will have to wait a little longer. Thanks for the wise insights.
It's also unthinkable that it's the parquet itself that is sagging. It's glued herringbone that's as old as the house, so the likely failure mode would be loose parquet pieces (which there are in some places). Possibly there's some type of board between the floor planks and parquet that could be sagging, but I haven't dug into that yet.
You're probably absolutely right that the best way to find out is to tear it up and start examining from above. The parquet is also nearing a renovation or replacement, but that will have to wait a little longer. Thanks for the wise insights.