Originally posted by FissionChips:

Weird misinformation in this thread from people who should know better. Tarred pieces are not immune to rain. Roof pieces, angled pieces, and stakewalls are.

It's not misinformation. You can check the wiki and compare darkwood beams[valheim.fandom.com] with iron wood beam[valheim.fandom.com], for example, or test it in game yourself.

The whole point of using tarred wood in construction is because it's waterproof, at the expense of being more flammable (which is also reflected in the game).