"We shape our buildings; thereafter they shape u.s" - Churchill
Wood entrance doors will last centuries, with normal paint/varnish maintenance. What is 'normal?' Simple answer: when cosmetically ugly, it's time to paint or varnish! It is vital to keep the wood sealed at all times, to prevent water egress. It's too bad that this vital principle doesn't always start at the manufacturer! It can lead to unexpected expenses To explain: recently we had to make two new church doors, 9' high, because they were rotted beyond repair. And....they were only 21 years old! Water had entered at critical points, and under trims, keeping them damp, because normal cosmetic painting was not done . Further, at time of their construction, none of the trims were sealed before assembly. Here's a pictorial of how we seal vital components AT TIME OF ASSEMBLY. Is this process new? Not to us: we are shipbuilders, for centuries, and as such, have taken care to make every effort to KEEP THE WATER OUT!