boarding loft joist question

[leaprojects]

Hi folks, I am boarding my loft
I already have a second layer of insulation down and the loft joists are 5x1 1/4"
I was planning on laying new joists between the second layer of insulation perpendicular to the loft joists. However I have been told (father inlaw) that the original joists won't take the additional weight and will cause the bedroom ceilings to bow.
Is this true?
Also the loft is 6m wide, don't think I'll get a 6m joist up there..
The loft is not intended as a conversion but will be used for storage..
Many thanks

 

[freddiemercurystwin]

What are the spans and centres of the original joists?

 

[leaprojects]

I'll measure and get back to you, do you mean how long are they supporting wall to supporting wall...and how far apart they are?

 

[freddiemercurystwin]

yes