Bouncing floor in living room

[spaxx]

Hi,

The floor in the living room was sagging. I have opened up the joists, and they are 70x195 cc50. I will later screw solid oak flooring 20mm directly onto the joists.

The span is 450cm, with the room being 700cm in length.

If I screw 1 piece of 45x195 on each side of the old joists, will that be enough? Or will the floor still sag even though it becomes 160x195mm?

Anyone with suggestions for solutions?

 

[Liteavvarje]

Prefab house ?
What is sagging, the joists?

 

[spaxx]

Brand house?
What is bending, the floor joists?

House from the 40s.

Yes, the beams are bending, you could say that. I want to minimize the risk of bending/vibrations when the kids run around it spreads and can be heard in the adjacent rooms as well.

 

[Liteavvarje]

Do you have a basement and any load-bearing walls there, had the same where there was a few mm between the wall and the joist, wedged in some shims, became quite steady, it all depends on the span.

 

[spaxx]

Do you have a basement and any load-bearing walls there? I had the same issue where there was a few mm between the wall and the joist, wedged in some shims, became quite steady. It all depends on the span.

Unfortunately, nothing like that. The room below is the same size and will remain so. Otherwise, I could have built a wall below to support it.

 

[Liteavvarje]

After I wedged up against the walls, the floor still sagged a bit; it was 45X210 (Norwegian measurement). I attached a 45X195 on one side, using a lot of regular wood glue and fairly close spacing with thick screws. A must is to clamp the new piece in place by using several clamps to pull them together. What can be important is that if you just place and screw, you'll have a slight sag in the joists; I propped it up with beams about 5 mm from the basement floor before fastening them. It wasn't completely perfect, but it stopped creaking and rocking in an unfavorable way, there's probably a bit left, but it's manageable and nothing we directly notice.

 

[justusandersson]

You need to increase to a beam width of 140 mm plus a screwed-and-glued 22 mm chipboard on top to reduce the deflection to a good level. You can achieve the width by screwing and gluing two 35x195 on either side of the old beam. Just two 45x195 are not enough. I assume that the old beams are of good wood quality. The new ones must be C24 or better.

 

[VW Transporter]

Krysskolva

 

[justusandersson]

Cross-bracing reduces the deflection somewhat, but not sufficiently.

 

[spaxx]

You need to go up to a beam width of 140 mm plus a screwed-glued 22 mm chipboard on top to reduce the deflection to a good level. You can achieve the width by screwing and gluing 2 pieces of 35x195 on either side of the old beam. Just 2 pieces of 45x195 are not enough. I assume the old beams are of good timber quality. The new ones need to be C24 or better.

How do you calculate?

Yes, the old beams seem to be of good quality.

If I screw an extra 45x195 on one side then? So a total of 3 pieces of 45x195. They don't cost much. Yep, C24.

 

[justusandersson]

What determines the deflection, apart from the wood quality, is the moment of inertia of the beams. This is a purely geometric concept calculated using the formula bxh^3/12. This means that a small increase in height has a greater effect than a small increase in width. You need to reach a total width of 190 mm to avoid adding extra height. It is screw gluing that is required to achieve full cooperation between the components involved.

 

[spaxx]

Thank you Justus,
I'll give it some thought.

Possibly a 45x180 limträ on each if I get a good price on it.

 

[justusandersson]

Cross bracing in combination with a screw-glued 22 mm flooring particle board would probably also work.

 

[Marive]

Check the price of kerto beams, not as nice-looking as glulam but cheaper and with higher strength.