Further strengthening of roof timbers

[cheshireblue12]

The surveyor recommend I install further strengthening of roof timbers due to the increased weight from concrete tiles.
I assume he means roof joists ?
Can any one tell me if this can be carried out with the roof in place ?

 

[joe-90]

You usually add a purlin before the (awful) concrete tiles are put on. Why did you put them on?

 

[cheshireblue12]

I didn't put them on they were already there.
Can I add a purlin with the roof still in place ?

 

[catlad]

You will need to open a section of the roof to get the new purlin in place but you should be able to leave most of it intact.