I'm not sure I understand the question. By dense, do you mean high atomic mass or high concentration in da house? By leaking out, do you mean from the ground or from the closed room?

On the longer run, BTW, the problem is not radon itself with its short half-life but its (not inert gas) breakdown products, which stick to dust particles (and cigarette smoke, hence the enhanced cancer rate in combination IIRC).

_{*Lunatic*, n.
One whose delusions are out of fashion.}