Rsj installation

[David hackett]

Hi

I’ve got 3 rsj’s on each side of my loft to support the new floor and dormer at the rear, my question is how do you install them straight as I’ve got no datum to measure from?

would you measure from the wall plate?

not sure how to go about this

thanks

 

[RandomGrinch]

A laser level sounds just the job!

Interesting video for context (starts @ 7:00)

 

[David hackett]

Yeah I get that, if I don’t sent the laser straight the beam will be out

 

[oldbutnotdead]

Posh laser levels are self-levelling (a rotary might be the easiest). Water levels work too & v cheap

 

[^woody^]

What do you mean by "install them straight"?

 

[David hackett]

I mean they might end up running out. So if I’m putting timer joist between they might be 6.5m at the start and then 6.3m and the over end. Or they might be 6.5m centres but running on a angle but the centres are the same.

 

[RandomGrinch]

String and trigonometry?

 

[^woody^]

Well, presumably the existing ceiling joists are square off two walls and parallel off two others. That might help.

 

[David hackett]

Steel will be running over the top of the ceiling joists. Maybe I should measure from the wall plate

 

[^woody^]

You might be better off getting someone else to do it.