If the floors are falling down then you have an underlying structural problem. Cracked floor joists, cracked support beams, wood rot. You would need to check the condition of the supports under the existing floor and have that repaired. Can't do a patch job that can cause further problems.
I don't think pallets are strong enough to fix falling floors. They are usually thin plywood.
You can build floors out of plywood. I will give you info on that to see if it helps you out.
Hello Brenda! Where are your falling floors located? Pallet wood would not be strong enough to repair floors that are structurally damaged. Once your floors are repaired structurally you could use pallet wood to fashion a very rustic planked wood looked flooring. I would only do that in a small area because it's probably not something that would last long and you would have to do a lot of sanding to have smooth wood to walk on and finish it with a few coats of poly.
This sounds like a structural problem. I would contact a licensed contractor to address it.
Like a sagging floor? If so, it's the structure underneath that isn't supporting the floor. You will need to check the framework and support under the floor. On top of the supporting framework is a sturdy subfloor and then the flooring on top of that. An old house we have owned had thick plank on top of the framing, no subfloor. Sometimes people make the mistake of weakening the supports for the floor, drilling or cutting into the supports, weakening them. Settling can also cause some sag.
I would not use pallets in the house. Most of them are treated with carcinogens that you would not want inside your home. If your floors are sinking, you have foundation problems. You really need to get someone in to check the foundation. This is not a DIY job and you need permits.
If its the subfloor that needs repair, I would recommend plywood or chip board. Most pallets I've worked with would not hold up for long to daily wear and tear.
Brenda....I do not believe pallets would be strong enough for a falling floor. You need to brace and use a good strong wood.
All of these comments are great.
Get a pro involved. Get multiple quotes.
Try to write a Scope Of Work with pictures to send the pros before they come out.