They're both correct.

Hi Irina, You can use both. "Wood" is what the tree is made of yes, but we also use the word "wooden" to mean something made of wood, similar to timber. You won't have any communication issues using either of them. Matt

A wooden beam is a beam made from wood. A timber beam is the exact same thing. Wood is the raw material, and timber is wood that is used to build things with. Timber has cognates in German (zimmer - a room), and in Russian (дом, домашнее), Latin/Fr/Spanish (domestic, domicile) and has the idea of house/building/ to build with. The words are interchangeable, but not in all circumstances.

I think that timber is technically felled, but unprepared wood. We have timber yards, where you can buy timber. Wood is just the material, a tree is made of wood, the table is made of wood, the beam is made of wood. Maybe you are confused because we call a collection of trees a wood, or woodlands? You can buy rough sawn timber, planed timber, etc, but it's all made of wood. So your beam is probably a timber beam that is made of wood. It's both a wooden beam and a timber beam. The reality is that most people will use both words somewhat interchangeably. As your specifically talking about construction, in England we would almost always use timber, or timbers for the components. - The roof timbers. - Framing timbers. - Timber framing.

I think 'wooden beam' is more common in the UK, certainly if you were viewing a house it might be described as having wooden beams but almost never timber beams. However a building might have a timber framed construction. In my mind, wooden refers more to a finished product and timber is more raw material.