hi. thanks for your reply. well this ply has been in this guys entry for some time before it was passed on to me and although it looks ok i would rather be safe than sorry as i am sure you know the problem it would cause if there was anything in it. my loft timbers are very narrow and supported by metal joist hangers. in fact there is quite a lot of metal and only the bare minimum amount of timber as my place was built at the end of the war when timber was scarce (hence the metal joist hangers) its just i would rather do something now just in case (however unlikely) rather than regret it later on.. i did get a very bad case of rot transmission in an extension back in the 80s and i had to replace the entire floor but that was through damp transmission which i sorted. and then there was another occasion in my workshop when i bought some victorian reclaimed timber which looked great but unfortunately had the rot in it and eventually went rotten that i had to replace that as well so i am sure you can see my concern having been bitten twice before..