Help determining joist direction

Hi. I am trying to determine the joist direction so that I can screw down my squeaky floors. The a frames of our roof are running as the yellow lines in he picture show. The directions state that the joists for the floor should run paralell to the narrow direction of the house. It says to measure 9 inches from the wal then 16 from then on out. I think I have hit one so far but the rest aren’t where I thought they would be. Based on my second picture I have the lines running the same direction. Where should I start measuring or how do I figure this out. It’s driving me nuts. There are two different walks on the left and I tried 9 and 16 from both but no luck. Thanks

 

Very rarely is the first joist at a set distance. It could be several inches to 16".

Is the picture on the right the first or second floor ?
Is there a basement below it ?
If there is a sheetrock ceiling below it you can scan for joist locations down there and transpose the measurements upstairs.

 

Hi. This is the second/top floor of the house. So I think I need to do what you are saying and get a ladder out and try and scan the kitchen and living room ceiling for studs. How much space is between the floor up there and the sheet rock below. I just freaked out for a second and was worried that I may have drilled a hole in the ceiling.

Is there anything I need to worry about hitting when using the scanning screw bit they provide? Wires or pipes or anything? Thanks

 

Ill scan the ceiling tomorrow and see how that goes. we are gonna replace the carpet with more carpet or hardwood sooner or later. maybe I just wait until we pull that up and get it all fixed. i don't know

 

Assuming an 8" floor joist there will be approx 7-1/2" between the floor and the ceiling.

By scanning I meant a device like this.... Zircon-StudSensor.
They're available at most home improvement stores.

 

Yes, thank you. I have two of those stud finders. I will let you know how it goes.

 

Good idea scanning the ceiling below. Looks like joists are running he opposite way of what I have in picture. The main area I am focusing on now is st the top of the stairs. Looks like a big air vent is running right under there however. You can see the vent in the left of the picture with my kid in it. I am attaching a new pic of the ceiling below. I was worried I may have poked a few holes in the vent but now I think it’s probably out of range for the drill bit.