Spots on Shakes

Hey Guys-

Do you know what these “spots” are on the wood shakes? The sellers disclosure indicated the roof was about 7 years old. There were a handful of places where the shakes were deteriorated and some warping and cupping. But I wasn’t for sure on the spots. Are those just the open pores of the wood? Some type of damage? It was mainly just on the part of the roof above the garage where there was no ventilation at all…would that have anything to do with it? Thanks!


Moss. . .

Is this the Northern exposure?

Hey Jeff-

The first roof picture is facing north and the fourth one is facing east. But yea, as I look through all the pictures, the areas that have the least sun exposure are the ones that most predominantly have that.

Does moss come and go throughout the year? What problems or concerns does moss entail for a wood roof?


kind of looks like old moss growth…pretty common on shakes, imo I would not make a big deal of it, for your cya rec a roof inspection then its off ur back.

Wood shake is crap to begin with. Moss just makes it crappier :smiley:

In most of SoCal, this material is not allowed for re-roofing or new construction, and prohibited (requiring complete removal) in many areas. My only recommendation when I see this stuff is to have it removed. So I can’t really address the “moss issue” other than to say, it will certainly accelerate deterioration.

Correct me if I’m wrong, as it’s been many years since I had to deal with wood shakes, but do they not require annual maintenance? Those sure don’t look like they’ve seen any!

Yep… sure do!

A little pressure wash might help.

I might be mistaken, but almost looks like this could be some extractive bleeding.

Tannin is a natural extractive of Cedar, Redwood and most other dark woods. It migrates to the surface of the wood when water is present and leaves an ink-like, coffee colored stain or overall darkness on the wood after the water evaporates. Tannin bleeding is unsightly, but not damaging to wood or any coating on the surface.

Tannin (or Extractive) Bleeding: Redwood, Cedar and Douglas Fir are examples of wood species that contain naturally occurring, water soluble chemicals that tend to migrate to the surface with exposure to extracting agents such as water. After rain or heavy dew, coffee or tea-colored stains may appear on the wood surface. If the wood is coated, discoloration of the coating may occur when tannin extractives are dissolved into the coating solution by water, reach the surface and remain as dark, coffee-brown stains after the water evaporates. This reddish-brown bleeding is unsightly, but not damaging to the coating.:slight_smile:

Kenny, it looks very similar to spatter from soft hailstones. They’re hard enough to remove some oxidation and dirt, but not hard enough to dent or crack shakes.

Is there a crop duster in the area?

See the way those marks are elongated and align with the wood grain. that indicates a liquid source of some sort. Also, the pattern is random. I’ve seen crop dusting and it appeared to me to be a fine spray. This looks like droplets. Was there any precipitation before the inspection?

Thanks for the link Jeffrey. I always read that wood roofs need maintenance but most of the time they don’t provide what that maintenance should entail. It was also nice to read a source that stated wood roofs don’t last that long…8 to 25 years. For whatever reason people seem to think wood roofs should last for 40 years. And I agree, it doesn’t appear this roof has had any maintenance.

Hey Gary-

It is in western Kansas but no, it wasn’t in the middle of a wheat field. It was actually in the middle of town so I don’t think it would be a crop duster. But I’ll certainly keep that in mind for the future as I don’t know that I would have ever thought of that and we do have a lot of crop dusting around here.


Hey Guys-

Thanks for your thoughts. I’m still not sure what it would be. I haven’t seen a lot of roofs with moss on it around here…it’s pretty dry most of the year and I didn’t see any presence of a plant-like substance on there. But since it does appear to be more prominent on the planes with the least sun exposure…that would make sense.

It does kind of look like something got spattered across there but who knows what or why.

We had a good rain about 5 days ago and a very light rain the night before the inspection. I looked into the extractive bleeding Marcel but I wasn’t able to find enough information to really indicate if that was the case here. My Google search didn’t really provide many pictures to compare it with.

And I did consider hail damage but wasn’t for sure.

Here’s a few more pictures. The first two pictures are the two roof lines that you see on the front of the house. The first is facing northwest, the second picture the roof is facing northeast, but obviously you can tell a difference between the two. The rest are from the sides facing south. I certainly welcome any additional thoughts you might have.


Due to lack of sunlight, these areas will stay damp/wet longer after rain or night condensation … could be mildew/mould beginning.

Kenny, I’ve seen wood roofs in Denver that were 65 years old.

Shake lifespan depends on a number of things.

  • the quality of shakes
  • installation quality
  • climate zone
  • roof pitch
  • direction of orientation
  • shake treatement
  • quality of maintenance
  • Location of the home

and more. There’s no simple, single answer.
If it were moss, you’d see moss, it doesn’t disappear seasonally.