Roof stained from wood smoke

boostnut · Mar 3, 2016

Here's a google earth pic of the roof of my house. The roof is 15 - 20 year old asphault shingles with some pretty serious staining directly to the east and to the west of the chimney. I have no doubt that the smoke is to blame, I installed my Jotul C450 insert about 3 years ago when we moved in. Prior to that the roof wasn't stained.

The question is whats causing the staining? I burn dry, seasoned wood. Primarily locust, maple, and oak. I always give the locust a full year to dry. Its split and stacked for the full year. My oak was cut and stacked in rounds almost 3 years ago then split and re-stacked about 18 months ago. I'm no rookie with this stove, I've had it in 2 different houses for a total of about 10 years.

I would like to think that the short chimney is to blame. Its an all brick chimney with a 6" stainless liner. The total liner length is only about 11'. I'm thinking of building a custom stainless extension to raise the height another 2' or so.

I currently have a block off plate at the old damper location and a bunch of mineral wool insulation stuffed in the top of the chimney. This same type of install worked well at my previous home where the chimney was about a foot or 2 higher from the roof deck. No roof stains to report there.

Any suggestions? Is this typical when your chimney only extends about 3' from the roof peak?

Highbeam · Mar 3, 2016

I would be up there to look for erosion/corrosion of the brick. It's not smoke stain. The staining is waterborn so it is being washed down your roof. A little bit of color from the brick will go a long ways.

bholler · Mar 3, 2016

I think it could be staining from creosote but it could also be from lots of other things like highbeam said. We need some better pics and you need to get up there to see where the staining starts and if there is anything corroding.

mellow · Mar 3, 2016

Most stains I see like that is from either creosote buildup dripping down or something rusting, I seriously doubt that is from wood smoke.

boostnut · Mar 3, 2016

mellow said:
Most stains I see like that is from either creosote buildup dripping down or something rusting, I seriously doubt that is from wood smoke.

I thought the same thing but there's absolutely no dripping creosote. The top of the chimney has a poured concrete cap that's clean, aside from a similar rust colored stain. Also, it really can't be rust. Its a brick chimney with a terra cotta liner and a stainless liner. Zero carbon steel to rust, aside from the cap which is painted and not rusting.

I'm baffled.

mellow · Mar 3, 2016

The 450 should have you burning clean so little to no creosote buildup, you should only be seeing white wisps when up to temp.

You have stains from the other penetrations on the roof, what is that from?

quotejso · Mar 3, 2016

I have the same problem I think it's my cap.It is a normal square chimney cap that fits on the 16x16 terracotta liner.The 6 inch flex is in the middle.For some reason the lip or lid of the cap just causes the creosote to build up and then it flakes down mixes with water.It's staining the stone chimney. I poured in the liner insulation not sure if it helped I think it's the type of cap. Anyone think switching to a regular circular 6 inch cap might help? Would that provide adequate protection from rain the top plate is sealed?

Highbeam · Mar 3, 2016

mellow said:
You have stains from the other penetrations on the roof, what is that from?

Pretty cool mold stains on the roof. New roofing has anti-algae and anti fungal treatments to fight it. The galvanization from roof jacks is often enough to stop the mold growth. You can see around the chimney that the heat from the chimney reduces moisture on the roof and reduces the black gunk there too.

The staining of the post is the iron/rust colored streak from the brick chimney. Same staining apparently exists on the concrete chimney crown.

Sprinter · Mar 3, 2016

I wouldn't raise the liner at this point unless you're having a problem with adequate draft. Eleven ft is a bit short, but draft is generally the only problem with a short flue.

If not rust, then I would think that it's some light creosote building up near the cap and getting washed down with rain. The top of the flue is where the first sign of creosote usually forms since it's the coolest part and isn't unusual even when you're burning well.

billb3 · Mar 3, 2016

Looks like you've got black mildew coating the roof. Th little white penetration vent thingies may be giving up a tiny bit of zinc/copper to kill the mildew/algae downstream when it rains. probably have the same thing going on with the brick/mortar/chimney cap, maybe just growing a different color algae/mildew.

Spray some diluted clorox on it see what happens ?

begreen · Mar 3, 2016

Looks like rust coming off of a galvanized top cap that is rusting. If this is the case, replace with stainless steel.

St. Coemgen · Mar 4, 2016

Smoke itself does not stain in vertical stripes down your roof. That stain is from water movement. You can see other stains on your roof from other vents that show similar stain patterns.

But the smoke can contain the particulate matter that is causing the stain. Like others said, if the stain is not from rust from the chimney collar, then it is probably from tar or creosote deposits that the rain is washing down your roof. Check if you have a lot of creosote or tar deposited in your chimney, and if so you may be burning your wood without enough air due to pyrolysis or smoldering. Open your air vents a bit more.

jetsam · Mar 4, 2016

Do you have rust stains coming out of your gutter downspouts?

The Principal · Mar 4, 2016

Wood needs to be drier. Build
up on cap is dripping down when condensation or rain is on your chimney cap.

Sprinter · Mar 4, 2016

Actually, I'm taken with the clean streaks from some of the galvanized (I assume) penetrations. I've always wondered if zinc or copper actually helps moss and algae problems and that pic seems to illustrate that it can.

Smoked · Mar 5, 2016

My liner is always very clean but I always have a little buildup on the mesh and underside of the cap that does flake off and stain my crown a little. My roof is darker so I don't notice anything there. I have plenty of green on the north side though ::P

begreen · Mar 5, 2016

Our stainless chimney goes up 7ft from the roof penetration. It's been up 10 yrs now and there is no roof staining. Boodtnut, can go up on the roof and take some pictures of the chimney? Or a least try a ground shot from a ladder?

boostnut · Mar 6, 2016

begreen said:
Our stainless chimney goes up 7ft from the roof penetration. It's been up 10 yrs now and there is no roof staining. Boodtnut, can go up on the roof and take some pictures of the chimney? Or a least try a ground shot from a ladder?

Had a bit of a ladder injury 2 weeks ago. With 3 fractured vertebrae, no, no ladders for me for a while.

Upon further investigation (with binoculars) I've concluded its wash down from creosote. Yes, my wood is dry BUT I'm obviously running the stove at too low of temps in order to achieve 8 or 9 hour overnight burns. There's build up on the caps screen, I typically get up there and clean it twice per year. Evidently its enough build up to cause the staining, confirmed by some stains down the sides of my brick chimney.

Lesson learned. Even if you let your wood dry properly don't assume you can cut the air waaaay down to extend burn times without making creosote.

Thanks everyone for the input.

Sprinter · Mar 6, 2016

boostnut said:
There's build up on the caps screen,

Yeah, that light, fluffy, crinkly stuff can accumulate on the screen. The guy that installed my system for me warned me that I would be having to clean the screen all the time and that I would have to remove the screen myself. He hated to have to install them. I did have some buildup the first couple of months but that was due to sketchy wood the first year, and probably some of trying to turn the air down too much. But the point is that the guy was wrong. It's not inevitable. I haven't seen a single particle in the past 4 years now that I know more about operation and wood preparation.

Thanks for sharing the experience.

Roof stained from wood smoke

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