To prevent cold floors in this situation you can add insulation between the ceiling of the room below and the floor of the room above or you can use carpeting in the room above to help insulate.
Flooring for cold floors.
Insulating the floors rim joists and headers can be an effective way to warm these floors.
Determining the cause of cold floors however is usually fairly simple and can be addressed without massive expenditure.
A cold floor is also an indication of a drafty uncomfortable house which makes your home a less desirable place to live.
Keep cold air out warm air in.
Another option is to layer a cold floor with large area rugs rather than wall to wall carpet and check the underside for dampness or mold growth occasionally.
You can expect the stone floor of your screen porch or the basement linoleum laid on cement to be cold and carpet is the logical warmer.
Some issues are structural and logical.
Luckily there are ways to combat this chilly predicament.
Start with the simplest solution which will help provide a comfortable temperature for the whole house not just the floor.
Floors of ceramic stone or concrete are the worst culprits with hardwood a runner up.
As an added negative impact of cold floors the cold conditions in your home will cause your heating system to work extra hard to combat it leading to an increase on your utility bills.
Glue carpeting to your subfloor material to minimize moisture penetration.