My home is 15 years old and I noticed the floor is squeaking more all over the house. I need help as to how I can find the joists of the floor to screw in some nails to stop it from squeaking. My tiled floor in the kitchen is driving me drive when I walked over it. My other rooms are carpeted and my entrance is granite. Should I just replaced the subfloor? But I have too much furniture to move out for the job.:mad:

There are kits available to eliminate squeaks, which are sold at big home suppliers. One type is used from below the floor. The other one that I know of can be used for carpeted areas by use of a double headed screw that breaks off at a lower elevation after it is tightened.
I have never tried with tile but the only choice (other than kit that works from below) I guess would be to remove some grout between tiles, find the joist and very carefully drive a screw taking care to stay clear of the tile. Movement in a tiled floor is definitely not good.

What kind of floor do you have? It isn't necessary to find a joist since there should be a 5/8" subfloor below your wood flooring. You can nail into that or try one of these special tools. Eliminate Floor Squeaks - Squeak-Relief - Squeeeeek No More - Squeak No More - Squeakender - asktooltalk.com

For the carpeted areas you can take a 4d nail and drive it into the floor to find a joist. Once you do, you can use typical drywall screws, just separate the carpet pile and put the screw in a hole in the backing and drive it flush with the floor. If you have berber I would recommend using one of the break away screws.

I would agree with "smear" on the tiled floor, try and locate a joist and remove the grout and go that route. I'd be nervous if there is that much flex in the subfloor under the tile and granite. You maybe able to carefully shim between the joist and subfloor from below but I'd be very nervous about cracking the flooring above. Good luck.