my local fat-cat builders not interested in the job so i am considering to DIY fit external bifold doors on the ground floor of my 2-storey timber frame brick veneer palace. this to replace 2 existing 1810mm door/window openings separated by a 562mm brick/stud pier. span will be a stunning 4182mm. any ideas what (internal, external or combined ?) lintle size i need ?
my libraries timber framing manual seems not to cover this span - does this mean steel is needed ?