Black Stain around Vent

Hi Everyone.

Was inspecting a roof yesterday and besides the more obvious issues, I noticed a Black staining of some sort around one of the roof vents and not sure what that might be from. Has anyone seen something like this? Photos attached.


Was it above/around a kitchen.
Looks like vent fan from a greasy, smoky stove top

Hi Marc,

The kitchen stove top exhaust actually terminates by the side of the building. This is a attic roof vent. That is something I will keep in mind though if I see it again.

Someone smoking in the washroom or they take a lot of showers and use the bathroom fan religiously.

Looks like those stains are the least of that roof’s problems…

What did it look like from inside the attic?

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Didn’t notice anything from there. Thanks

Thanks Peter, interesting insight.

Pretty tough to tell, especially if there’s no sign of similar discoloration in the attic. It could be particulate-based like smoke, or an accumulation of aerosolized grease, or is could be a chemical reaction. Luckily, you don’t have to identify the source.

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Appreciate the feedback.
Happy July 4th.

I see this a lot; I figure it’s from dust in the attic.

What would/could cause, discoloration in the mineral/granular of three tab shingle? Hmm?

Low profile roof.
Covering. Organic or glass fiber mat 3 tab shingles.
Poor condition.
1: Prior repairs. Around the plumbing vent.
2: Wide slots.
3: Granular loss.
4: Mechanical damage. Ends of tabs.
5: Exposed shingle mat. Various locations.
Suspect" The roof covering, shingles have surpassed the normal life expectancy.
Refer to recommendations in the roofing section.

Roof deck vent. Low profile.
No adverse conditions observed the day of the inspection.

Plumbing flange.
Exposed ABS vent stack.

Recommendation: Roof.
Recommend a licensed roofing contractor repair noted defects, deficiencies and provide a roof tuneup immediately, to insure the roof is weather tight.
Recover the roof within 1-3 years.
Act upon any recommendations therein.

The buildup of black dirt on the outside of attic vents could be caused by any combination of moisture, cold air, warm air, static electricity, air currents, and supply of dust, soot, and other particulates that can drift with the air.
Similar conditions occur on interior diffusers and return air grills in some buildings. Plain dirt.

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Thanks Marcel and thanks Robert as well for your detailed reply.
I learn something new everyday.

You got that right

  1. Exposed mat is white. The area circled in the photo is black and is exposed asphalt due to missing granules.
  2. There’s nothing wrong with exposed ABS… very common, including most of the western USA.
  3. The wide slots in alternate courses indicate a racked installation, almost certainly not the manufacturer-recommended installation method for this type and model of shingle.
    Racking is typically recommended for only a few dimensional shingles, not 3-tab like those in the photo.

1: Loss of minerals granular exposes the thick bitumen layer and mat. Thanks.
Observation: Single Wear, Cracking & Granule Loss.

2: Hear is what I read about exposed ABS plumbing pipe.
Some local regulations require ABS pipes to ‘contain pigments’ to protect it from UV radiation or to ‘be painted’ with latex paint. Exposed ABS goes in my reports the same as exposed ‘cast iron’ vent pipes. Observation: Missing pipe flashing.

Kenton, maybe its just me but, look at ‘all the wide slots’ from shrinkage on the roof deck, not only the wider slots due to course alignment/correction.

With racking, I would expect 1,2,3 courses required correction. The wide slot would be on one side of the shingle, not at both ends of the shingle.
Likely shingle the installer was installing seconds and used chalked lines to keep the courses in line, but again did not install the roof.

Story. When I was roofing, IKO manufactured shingles in Quebec. The government of Quebec warned the company several times about quality control due to consumer complaints. The company was fined and told make improvements. They moved ><30 miles West to an Ontario border town instead of updating the Quebec manufacturing plant. When we installed shingles, we being the company and men I worked with, you chalked squares vertically and horizontally. You being me, or anyone with the sense. Lol. You/me/us/we would watch as poorly manufactured shingles deviated away from chalked-lines. Quality control was out of control. Lol. Started using Domtar and BP roofing products after that.

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Hi Robert,

  1. Until I went to Florida, pretty much 99% of all plumbing stack pipes I had seen were ABS. They do have pigment. It’s black. I’ve almost never seen them painted. There’s really no point to it.

  2. I don’t know why they increased spaces between shingles in the same course, but my guess is that it had something to do with money. The joints between shingles alternating straight up the roof instead of in a stairstep pattern definitely indicate racking.

Morning Kenton. I have read several articles on thermoplastic weatherablity. Sill reading other articles.
When making a determination for the suitability of a particular plastic material for
either outside storage or long term above ground service, the environment
surrounding the piping material must be considered. A brief description of the more
important environmental parameters follows:

3.2 ABS (Acrylonitrile-Butadiene- Styrene) Terpolymers
Impact-modified styrenic polymers such as ABS (acrylonitrile-butadiene-styrene)
terpolymers are very sensitive to oxidation, essentially because of the butadiene
content. The carbon-carbon double bond (C=C) from butadiene, which is responsible
for the elastomeric behavior of the rubber moieties in the material, is extremely
sensitive to UV energy. This energy causes oxidation and crosslinking that modifies
the material’s rubbery behavior that is responsible for its impact resistance to one of
a more brittle nature. Degradation from weathering starts at the surface and may
propagate through the bulk material, resulting in a rapid loss of mechanical properties
such as ultimate elongation, toughness, and impact strength.

ABS pipe usually contains sufficient carbon black to provide protection from sunlight.
The effects of ultraviolet radiation are substantially reduced in black pipe which
enables its use in outdoor applications. The largest outdoor use is probably plumbing
vent pipes of drain, waste and vent (DWV) systems that are fully exposed to all
climatic conditions.
No adverse effects have been reported from other weather conditions such as wet or
cold, or from geographical location where the intensity of ultraviolet radiation varies.
Non-black ABS compounds are not recommended for outdoor service.

Who cares! :smiley:
The roof is shot!