Hello!

We are currently working on a Pergola structure in Northern California. We were recommended Parallam beams by our structural engineer for our pergola build and were told by the lumber company that we could use them in exterior instances as long as they are covered/ weatherproofed.

Now that the structure is going up we are wondering how the best way to do this. Before we really sat and talked about it the guys had already primed and painted the would with an exterior sealing paint. They claim that it is enough to 'weather proof' the wood. I am a bit concerned that the various crevices in the wood... even if painted in have the ability to hold onto water and may compromise those areas.

We are considering covering the rest of the exposed beams with aluminum flashing and sealing all edges. Would this be enough to waterproof it, are there any risks associated with doing it this way? We would nail or staple in the flashing and seal those spots and the edges. We appreciate any times or recommendations on how to proceed.