What is this

[gash2024]

Ive just been in the loft putting the new insulation in and ive spotted something thats got me a little worried, theres a hole in the felt for starters about the size of a small plate and some of the timber on the same side (rafters) has a white/yellow stain on it and the area smells like mushrooms am i right in thinking this could be dry rot? the timber seems dry but i dont know if this is a previous stain or its dry rot growing.
What can i do about the hole in the felt and more importantly how can i test for dry rot.

 

[Symptoms]

gash - when you say "felt" do you mean glassfibre insulation or felt insulation (wool felt was used)? Also it might be useful for diagnosis for you to post a picture of the offendeing area. Holes in insulation are often caused by bird/animals (squirrels, rats, mice, etc.) - do you have any access holes in the roof covering, soffitts, etc.? Staining could be from their latrine mess. Could there have been a drip from the roof covering?

Dry rot DOES need a moisture supply (this can be local or some distance away). Look for thin whitish threads (like thin roots) leading from the area. If this mystery is very localised, don't worry as there will be an easy fix.

Post a pic.

 

[gash2024]

I say felt because it looks similiar to felt you might find on a garden shed, its the stuff thats layed on the roof and the tiles are put on top of .
I cant see where any water is getting in as the area feels dry and the roof space seems dry, there isnt any roots its almost as if its just a white stain thats a little fluffy but its not growing away from the timber.
I will get a picture as soon as i can.