White Powder on Attic Trusses

I found this white powder along the trusses in a home. The roof sheathing and trusses were dry, but there is plenty of evidence that they had condensation problems prior to installing the new roof (metal) ridge vent the length of the house, and baffles to keep the soffit vents clear.

The white powder wipes off readily with just your hand, the vertical line was created by doing this. If it were on crawlspace concrete, I would call it efflourescense. It is that dry. There appears to be no damage to the truss material, and it is only on the trusses, not on the sheathing, and seems top be localized over the attic entry and bathrooms.

Any ideas what I am seeing?



Might be Baby Powder,that stuff just flys thru the air. My misses uses it after taking a shower and I have to keep cleaning the vent fan all the time.:roll:

It looks similar to that in the third to the last picture here:

Hi. Larry and Happy New Year.

Was looking into some of the causes of this baby powder and found that excessive moisture might be the culprit.
Seen this before and found that evidence of the dark plywood sheathing, the powder that seems to evolve when things dry up can and will eventually turn to dry rot situation.
Not enough ventilation and moisture is causing it, but it could also be promoting a mold and this powder is what is left when in the dry State. Could activate later with moisture from what ever the problem is with this attic.

Your link does not seem to work.

Marcel :slight_smile: :slight_smile: :slight_smile:


Here is the correct link:

Thanks, Michael. I don’t know how I got a double addy in there.

Happy New Year back at ya, Marcel. :smiley:

So what are our deductions at this point to help out Johns Posts.?

Moisture from bathroom exhausts?
Not enough ventilation?
Not enough insulation?
And specifically, what is that white powder?

Open for interpretation myself, curious.

Marcel :slight_smile: :slight_smile:

My mass spectrometer is down for maintenance. Call CSI.:wink:

Where do the bathroom vents terminate at? Another possibility is that the roof rafters/trusses got a good soaking rain on them right before they installed them and maybe the plywood was covered or not on site yet and didn’t get wet. How old is the house? How many trusses have this? all of them? I leaning towards mold.

All are possibilities but it is a little hard to discern from here.

Could someone bring the house a little closer, please? :stuck_out_tongue:

I could only guess at what caused this, and your best bet is to describe it, as carefully as you have done, include your photo documentation, and recommend a second opinion. PS Don’t forget to disclaim any further responsibility.

Great post well explained and I love all the replies and information given by many . Thanks to all
Roy Cooke

I’m still thinking about it, and more and more I’m inclined to move toward suggesting that it might be some form of a fungus growth, and would actually refer to it as such. Then, you could recommend a termite inspector, unless your client is an attorney, in which case you should recommend a mold specialist.

Hard to tell from just a couple of pics but the left photo there appears to be a hard edge where the white material starts, almost like some kind of overspray and the truss had something lying on it that prevented the spray from covering all of the wood. The second photo it only appears on the one truss member and not on adjacent ones and not on the sheathing as well. So from that, it appears to me the white material was on the trusses before it was installed on the house. We find all kinds of strange stuff on the undersides of sheathing, trusses, etc. (i.e. muddy footprints, paint, tire tracks,) I am more concerned with the dark wood stains around each of the roofing nails protruding thru and the rusty tips of the nails. Both of these indicates water seemly seeping in around the nails or very high humidity inside the attic and the water droplets are condensing onto the cooler nails and leaching into the wood sheathing. Ive see both. The moisture, humidity could be coming from the bathroom vent fan as you indicated this is the vicinity of the white stains. It could be mold but the only way to tell is to have it analyzed by a lab. As stated, write your findings up, but be careful about “guessing” and stick to the facts as you see them. If you don’t know what something is, say so. Good catch though. A lot of HI would have gaffed this off and said nothing, hoping it was okay.

I think it is something that was on them before it was in place as you see it is not on the sheathing.


Your pictures are OK, but I’m unable to really get a good view of the white substance.

I would ask the owner/seller if they have had any PC svc. in the attic area for either Moisture or maybe Roaches, Silverfish, Ants, etc.

I/We, in my Pest Control days used various products (usually Dusts), in Attic areas for the long term control of the above insect infestations.

Just guessing here, but it does look similar to power dusting applications, at least in our area.

mold…you’ll know when you come down with the nasty respiratory infection.

All very good responses and a great topic for the MB. From the visuals and from my experiences I would not describe this as mold and recommend further evaluation via sampling of air and swabs of the truss(es). The report will comfirm wether or not it is mold and if indeed it is harmful. In either case it does appear that it is from water intrusion or humid conditions in the attic area. I too would continue to stress disclaimers.:slight_smile: </IMG>

Recommending further evaluation, I believe would be the best bet at this point, wouldn’t you say?

Marcel :slight_smile: :slight_smile: