Attic roof sheathing Black?

[Paul Sew]

Can anyone explain why the sheathing is black on one side and the other not. The roofing material is a torch-on and re-roofed around '07. The attic is dry in a 1973 home. Roof vents are adequate insulation is very uneven but the black area on the sheathing is very uniform.

[Richard Burkard]

After Looking at the pictures, it appears the roof sheating is grey, not black. The sheating appears to me to be that it was used to form concrete and and then used as roof sheathing. That was a common practice back in the 70's and 80's. Are you sure the discoloration is a mold?

[Terry Mullinger]

Re: Roof sheeting was likley concrete form salvage:
Yes I agree: This was very common, you can see where the form strucure was removed before the sheeting was re-used.

[Eric Barker]

Paul, Is the stained exposure facing north? This is generally due to that side not receiving as much sun as the south. From your photos it is evident that the top chords of the trusses are also affected.

The conditions that you see today may not be what was present years ago. Perhaps there WAS some problem that has been corrected by a previous owner. In any event the staining that you see is likely to be mold - only lab testing will confirm that. Mold will go dormant in dry conditions but that does not mean that the spores are not an issue.

Now there's the thought that air in the home generally moves up through the structure and therefore what's in the attic should be ok. That may be true but many homes have been altered from their original construction and are more air tight. With exhaust fans that are now installed, especially the high air flow units the living areas can become depressurized where by attic air (and any spores) can be pulled into the interior.

[Wayne Carlisle]

I agree with Richard and Terry. Looks like form boards.

[Raymond Wand]

The darkening is only on one side, too delineated for ventilation issue or mould issue. Also note what appears to be the removal of a rafter.

[Paul Sew]

Gentlemen I thank you for your input. As my first thoughts were the boards were sprayed with some sort of fire retardant and the forming boards also made sense. When in the attic it was clearly black and the surface was dry at a Northern exposure. As Eric mentioned it could've been a past issue. So I've concluded it being mold/mildew as Eric stated. The confirming factor for me was this thread: http://www.inspectionnews.net/home_inspection/attic-areas-home-inspection-commercial-inspection/7039-black-roof-sheathing.html
with almost very simular pictures. Again thank you for the input everyone. I used to be just an on-looker for valuable info but hope to participate more in this community.

[Raymond Wand]

Dab a drop of household bleach onto a suspected spot. If the stain loses its colour or disappears, it may be mold. If there is no change, it probably isn't mold.

[Paul Sew]

Thanks for the tip Raymond.

Oh, just to add. When I looked closely I did see spot marks underneath all the black.

[Raymond Wand]

Paul

The only definitive way to know if its mould is to have it tested by a recognized laboratory.

[Paul Sew]

What would one say to a client about this situation? Would like to here some explanations or recommendations.