Mildew on siding

[Bossard Steven]

I inspected a house with cedar siding with a natural finish. The house is very nice and well maintained. It was in the process of have the exterior stained and sealed. There was mildew on the siding, it was speckled with black dot. However tere was no mildew where the studs are. Any suggestion to the cause with be greatly appreciated

[Scott Patterson]

I inspected a house with cedar siding with a natural finish. The house is very nice and well maintained. It was in the process of have the exterior stained and sealed. There was mildew on the siding, it was speckled with black dot. However tere was no mildew where the studs are. Any suggestion to the cause with be greatly appreciated

Photos would help...

Sounds like thermal bridging, similar to ghosting we see on drywall.

[ROBERT YOUNG]

I love to see images.
Shakes or shingle?
What grade ( quality )?
Shakes and shingles are applied differently. Exposure.
Also method of application is important. Thermos bridging may be an indicator.
Inadequacy in insulation, vapor barrier.
Mildew + black dotting. Possible mold growth.
Before staining
I would recommend IAC2.
May have migrated into the home.
Lots of variables. Photos would help.
1.) In a shaded area. 2.) around the total perimeter of the unit?

[Garry Sorrells]

Since it is cedar siding. If untreated (new) or old being retreated could be a lot of things.
1) Mold
2) Fungal
3) Chemical reaction with something contacting it in milling operation
4) Chemical reaction with air born contaminates (power plant, local industry)

With out pictures and a better description it is any bodies guess.

[Gunnar Alquist]

Bossard,

I will occasionally see mildew staining on the exterior siding, typically on the north side under certain conditions (typically tree-shaded lots). If the walls are insulated, the staining will be between the studs, where the siding is the coldest. The studs will conduct heat from the interior and keep the siding warmer immediately adjacent to the studs. The siding over the stud bays becomes colder and allows condensation to form on the exterior, creating an environment conducive to mildew growth.

[Tony Cole]

Just curious, when you say speckled with black dots, how do you mean that? Speckled, or what looks like splattered with black dots that are hard to remove but can be scratched off is a type of fungus that comes from hardwood mulch. It will form on cars, siding, basically anything it can attach to. Google "artillery fungus", that is probably what you have, if I have taken your description correctly.

[Garry Sorrells]

Bossard,

I called the psychic connection but they were no help. Need to see what the discoloration looks like.