I'm no expert, but I've had some experience - it all depends.
I have an oak house number on the North corner of my house that gets little
weather and no direct sun, it only has a couple of coats of spar varnish
and looks great after seven years.
I have oak front doors that face South-East that gets no weather but gets
direct sun. The doors need attention every couple of years.
The ultra violet rays penetrate the spar varnish and affect the wood underneath.
Since I need to replace my back door this year, I have been checking out my options.
One website explained what to do, but wood still generally needs attention every couple of years.
The best advice should come from wooden boat owners - I'm not one.
Ken,
V-1, 2, & 3
When the People fear their Government, there is Tyranny.
When the Government fears the People, there is Liberty.
- Thomas Jefferson
You must be the change you wish to see in the world.
- Mohandas Gandhi