And if there is no basement?

Gideon wrote:

The important point is that radon is a danger to you or your pets
only if you breath it. If you are breathing it, then your risk level is
dependent upon the radon level in the air that you are breathing
and the length of time that you are exposed.

Pets, especially cats, are often at the greatest risk since in some
homes they spend a lot of time at ground level in the basement.
A person who spends much of the day in a basement home office
and a lot of free time watching his large screen basement TV may
also be at relatively great risk.

Radon is 9 times heavier than air and it tends to stay low in the
basement. Basement venting can greatly reduce radon levels.
Negative pressures in the house greatly increase radon infiltration
into the basement and subsequent radon movement up to the living
areas. Exhaust fans are obvious culprits. Air movement such as
that created by the furnace blower fan also increases the spread of
radon through the house. Cracks in basement foundations,
cracks in basement floors and openings such as sump pump pits
all increase infiltration.

Better than guessing, buy an inexpensive radon test kit, use it
correctly in your basement, and then send it to the lab. If the test
results indicate high radon levels, then buy a couple more test
kits and test your living areas. I have a friend whose basement
tested at 37 microcuries - a level considered rather dangerous.
But the upper levels of the house have acceptable levels of radon
and the family is relatively unconcerned since the basement is
just a place to house the furnace, water heater, washer, dryer
and a lot of junk.

They feel secure with just simple steps such as cracking open
a window when an exhaust fan is running, opening basement
windows on occasion for some basement cross ventilation, opening
living area windows briefly once in a while during the winter, etc.

Like cigarette smoking, radon can be very dangerous and can
present a greatly increased RISK of cancer. Like second-hand
smoke, radon dangers can be greatly exaggerated.

Gideon