I'm working on a old terrace at the back there is a single extension for kitchen bathroom I want to take out a wall that is supporting 2 purlins that have been tacked together so what I proposing to do is to strap eithier side with 6x2 timbers and bolt apply brackets over joint the length of first purlin is 4 metres and the other one is 2 metres how long will the strapping timbers need to be ??