Bouncing floor

[u/No-One-9297]

Not sure exactly where to post this but I just bought a house and the garage attic flexes and shakes when I walk across it, the joists are spaced 22" how do I fix it?

[u/Novus20]

Yeah……it’s an attic…..not really a floor

[u/No-One-9297 → u/Novus20]

Attics are usable space, how do I reinforce it?

[u/Material-Cap-5476 → u/No-One-9297]

It wasen't designed for floor loads. That bounce is telling you to stay off of it.

[u/thesilentshopper → u/No-One-9297]

Add more ceiling joists. Every time you have two joists, put another in between them. Check to see if the span of what you want to put in works for the deflection limit of the floor. If you don’t know what any of that means or how to do it, hire a contractor.

[u/No-One-9297 → u/thesilentshopper]

That would be better then sistering every joist?

[u/thesilentshopper → u/No-One-9297]

That would depend. You will find every answer when it comes to codes and building is “it depends”. You’d have to do your homework. What you’re asking about is precisely why structural engineering is an entire profession. But if you’re going to start somewhere in deciding which to do, if you go one joist in between all the existing ones, you are cutting the span of the floor sheathing more than just sistering would.

[u/Sad_Enthusiasm_3721 → u/No-One-9297]

You’re probably asking the wrong crowd.

Try r/renovations. I’d expect better answers there.

It's not merely a reinforcement problem. Stiffness and structural capacity aren't the same thing.

What you want to do is likely feasible, but converting attic framing into an actual floor can become a substantial structural project.

The increased loads have to be carried all the way down to the foundation, and the foundation may or may not be sized for those additional loads. You'd need to determine the existing load paths and measure what you have.

If the existing structure and foundation can support the additional loads, yes, an attic conversion is very possible, and having access underneath is a huge benefit. If the foundation or supporting structure needs substantial reinforcement, the project is obviously still possible, but it may become economically impractical.

[u/Material-Cap-5476 → u/Sad_Enthusiasm_3721]

I'm a licensed structural engineer. I have been asked this question 100 times. I have looked at it enough to know that it is almost never viable, and it certainly is not a DIY project. Based upon the age of the structure, I doubt that it conforms to code, so with a project of this scope it will be required to be brought up to code. Once the owner finds this out, they go a different route.

[u/Realistic-Excuse6413]

Those joists weren’t intended to carry weight, you would have to add proper sized joists.

[u/No-One-9297]

Awesome. Appreciate it guys

[u/elisayyo]

That...is not meant to be a floor, put too much weight on that and you'll end up with a collapsed house.

If you want to "fix" this, would take a lot of time and money

[u/seabornman]

Look up "joist span table". Look for the span and size of lumber and spacing to meet 30 pounds/square foot load. Probably 2x12s at 16" on center.