What is this? photo

This is inside attic on underside of roof sheathing. New roof was installed 4 years ago. It this old water stains (appeared dry now), what is the white stuff?


“Unidentified fungal growth”

Suspect microbial growth

Thanks, should I recommend a mold inspection?

I would first recommending mold conditions, and then kill the mold.


I would FIRST recommend that the roof be fixed.

The dreaded mold will be in the dumpster then, but you can still test the outdoors if you want.

Will the roofer know to remove the roof sheathing that contains the “unidentified microbial growth”?

Yup, It’s a simple roof leak.

You don’t need to test for Mold. Simply recommend roofing material to be evaluated and corrected for leaking. Sheathing in this area must be replaced. It’s an Active leak if the roofing material is not new.

I would have used my moisture meter here to determine if it was an active leak or not.

Here is a good starting place if you are not familiar with Mold (or Mould for our neighbors to the North). This is only one of about a thousand websites that popped up when I typed Mold into Google.

Thanks, I just had not seen white mold before.
This NACHI forum is a great resource, thanks to everyone.

It comes in all the colors of the rainbow.

Hi Gents!

Regarding Rusty Keith’s question, I think that David Valley hit the nail on the head.

In truth, it is less important to determine IF it is mould than determining what caused the water staining and does the source of water exist at the moment; this is the primary question.

The white material may or may not be mould. In fact, it may or may not be a fungi at all. It actually is not too important to find the answer to this question, since resolving the primary question (above) will render this secondary question moot.

[FONT=Arial]But then that’s just from a fishin’ fool in Colorado. Heck I think its important to stand in the middle of a stream for endless hours, so what could I possibly know, eh?

[/FONT]Rusty Keith, I’ve put up a ton of mould and fungi photos at

You may find page useful. By the way, “mould” is just a qustion of shape and form - it is a classificaiton based on appearance only Some fungi could be a yeast one day, a mould the next, and then … And then there are some REALLY wierd ones call “slime moulds.”

Caoimhín P. Connell
Forensic Industrial Hygienist


(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)


Welcome Back Caoimhín.
As per usual great info thanks for visiting …Roy

How was the ventilation of the attic area?

Great comments everyone, thanks! The ventilation was OK (two large box vents on each slope and soffet vents). The leak was not visible from top of the roof, I missed it until I got into attic.

This is my first time posting on NACHI, I would like to say hello.

Is this the only area that is affected? Unless it is widespread I would not jump up and down screaming mold and reccommending “tear out the roof”.

As David and Caoimhin advised, get the leak fixed. If I was really concerned I would suggest cleaning and monitoring. If you want to use the words “licensed mold remediator”, you could. But, in my head any handy man could clean it up.