wood grades swedish wood i joists faqs elliotts tech2 html glued laminated timber glt m about glulam swedish wood evolution of building elements dimension timber timber development uk tech2 html structural elements swedish wood single span ridge beam faux timber beams authentic looking tech2 html dowel laminated timber panels what beam size do i need uk work i joists faqs elliotts treated timber 6x2 150mm x 47mm timber beam design step by step glued laminated timber glulam