Firrings question

[Glenn83]

Hope i can get some help on this one

Flat roof is going on for the extension building control came today and said we need to BACK STRAP THE FIRRINGS.

Can i get some advice what is this my roofer has never heard of it before either unless its another temology for something else.

The roof is made with posi joists firrings all in place just not sure what back strapping them is?

Thank you in advance everyone

 

[RrogerD]

Try Google.
It says, the firrings are fitted to the bottom of the joint rather than the top

 

[Glenn83]

Try Google.
It says, the firrings are fitted to the bottom of the joint rather than the top

To be fair thats the first place I looked. The firrings are fitted to the joists? What do you mean bottom of the joint?

The answers I get from Google are not making any sense