I'm going to build a pergola and need some 20' 2x8's. Menards apparently does not stock these in the store but offers free shipping to the store. Another alternative would be to get 12' long boards and join them with a 1/2 lap joint in the middle (or if there are better ways to join them I'm all ears). Would this be as strong as one long board? My design only have corner posts and no center posts.

Thanks
Mike