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The Inspector's Journal

Vinyl Siding Stains


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I have never seen this type of staining on vinyl siding. The home is a 1997 build, 3/2 on a slab. The side of the house that you are seeing is a west exposure. There is a master bath and master bedroom on the second floor opposite the staining and a dining room and living room under the bedroom. The home was immaculate. I licked the stains and my tongue did not burn and all I tasted was pollen.

Does anyone have any idea what may have caused the staining?

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How did you deduce that the house has furring strips? Does it? Do you also assume this ghosting is of no concern to the buyer other than cosmetic?

No Mike, I'm not assuming anything for the buyer. That is only the theory that came to mind from what I saw from the picture. But then again, I wasn't there so I could be way wrong.

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Very typical "ghosting" pattern... You are seeing the 2x4 studs and if you look close you cans see the second floor band joist. Those are not furring strip patterns and it does not necessarily mean the insulation is bad or the vinyl was installed wrong or that the home has a problem.... The staining is from dirt/pollution in the air.

The wood framing is colder/warmer than the vinyl and this effects how and what is attracted to those areas. We see the same thing with drywall in homes with smokers or folks that burn candles in their home. You also see this with EIFS cladding.

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...and it does not necessarily mean the insulation is bad or the vinyl was installed wrong or that the home has a problem.... The staining is from dirt/pollution in the air.

I see this very rarely. Maybe twice or three times ever. There are probably different dynamics down in Georgia.

What would be an example of this ghosting showing up if there is good wall insulation? I doubt many homes are built with steel exterior studs.

And wouldn't the stud lines be darker if the discoloration is from air filth?

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...and it does not necessarily mean the insulation is bad or the vinyl was installed wrong or that the home has a problem.... The staining is from dirt/pollution in the air.

I see this very rarely. Maybe twice or three times ever. There are probably different dynamics down in Georgia.

What would be an example of this ghosting showing up if there is good wall insulation? I doubt many homes are built with steel exterior studs.

And wouldn't the stud lines be darker if the discoloration is from air filth?

It all has to do with thermal dynamics(way outside my knowledge base) and how heat and cold effect the attraction of particulates in the air. The stud bays are insulated but the wood framing is transmitting or conducting the temps at a different rate and this is basically what you're seeing.

Might also be missing the WRB on the substrate, very common with pre 2006-07 homes.

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...and it does not necessarily mean the insulation is bad or the vinyl was installed wrong or that the home has a problem.... The staining is from dirt/pollution in the air.

I see this very rarely. Maybe twice or three times ever. There are probably different dynamics down in Georgia.

What would be an example of this ghosting showing up if there is good wall insulation? I doubt many homes are built with steel exterior studs.

And wouldn't the stud lines be darker if the discoloration is from air filth?

It all has to do with thermal dynamics(way outside my knowledge base) and how heat and cold effect the attraction of particulates in the air. The stud bays are insulated but the wood framing is transmitting or conducting the temps at a different rate and this is basically what you're seeing.

Might also be missing the WRB on the substrate, very common with pre 2006-07 homes.

Right. Brownian motion.

And an uninsulated wall will accentuate the temperature differences and cause the studs to become more of a magnet for condensation. A well insulated wall will not have this dynamic. That's my theory anyway.

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