The web method worked.
I installed icedtea-web 1.6.1, which provides javaws, then using the jnlp file http://www.sweethome3d.com/SweetHome3D-NoOffscreen.jnlp from the FAQ:
Or to just to change the measurement unit, edit ~/.eteks/sweethome3d/preferences.xml to a sane value:
<entry key="extensibleUnit">METER</entry>
or
<entry key="extensibleUnit">CENTIMETER</entry>