Thread: Black spots on underside of roof

Hi,

I'm not an inspector buy could not find a forum that have the experience you guys do. Our house was built in 2006; it's a two story house with a unheated connected garage. Both buildings have hip roof. We have two bathrooms on the 2nd floor, their fans vent into the soffit on the east side of the house ( I want to correct that at some point).

Two weeks ago I put in a layer of R30 insulation as all I have was R19 at the time. I went into the attic today to replace a J hook I broke holding a PVC pipe up. While up there, I noticed that there were rust spots on my new white insulation. I touched them and they were wet. I looked at the bottom side of the roof, and saw many black spots. Keep in mind, when we moved in 3 years ago, those spots were there, but I'm not sure if they were that many. I touched the nails and they seemed damp. I felt air coming in from the soffit baffles which is a good thing and could see down into the soffits from them. The insulation is not blocking the soffits from what I can tell. I sealed up around PVC pipes running down into the house with spray foam before I installed the insulation.

I pulled back one area of insulation and felt some water, something I've never felt before while up there. I don't know where that could have come from. We do not have an attic vent either.

The side that has the darker spots (all sides do) but the worst is on the northern side of the house. I'm not sure if we have a proper ridge vent, I'm going to get on the roof today and find out.

Here's a link to the photos: https://skydrive.live.com/?cid=b7361...57021E58%21831

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99.9% sure it's mold. Usually from a lack of ventilation and/or too much moisture in the house. I'll assume things are pretty much the same in Maine as they are here in Oregon since we're roughly at the same lattitude.

I'd guess it's worse on the north side of the attic and/or where there is less sun exposure (overhanging trees, etc.). It's actually very common around here. There's really two parts to your problem - #1 is stopping what's causing it and #2 is remediating what is there.

#1 can be easy or hard and without being there it's tough to say. Common causes of excessive moisture are cooking a lot in the house with poor ventilation (re-circulating range hood rather than exterior venting type, for example). Also, bath fans improperly routed or not being used can do it. Or, something I see in apartments a lot, over-occupying. Meaning 6 people living in a one bedroom apartment. Just too much moisture (more showers, more cooking, etc). A wet crawl space can also contribute to the problem. And, of course, the most obvious.... does the attic have enough and the right type/placement of vents? Without being there I can't say.

#2 (remediation) is typically not a huge deal for what I see there. It often invloves washing with a bleach solution and maybe spraying on some anti-fungal encapsulating paint. Keep in mind, though, that if you don't take care of the root cause the remediation will likely fail. Also, for your protection moving forward and when you sell the house someday you should really have it professionally done and get documentation to keep with the house. Buyers get SUPER freaked out by mold.

In all likelihood, moist air is leaking up from downstairs. Warm air carries moisture.

You may need to peel back some of the insulation batts and seal around openings such as light fixtures and the top plates of walls, and check bath exhaust ducts and so on. Also seal around the attic hatch. Double drywall makes a heavy hatch. Seal around the edge with weatherstripping.

I see a ridge vent in the pics. Make sure from below that the roofers didn't cover the vent slot with roofing paper.

Which way did you run the insulation, parallel with the joists or perpendicular with joists?

From photos it looks like many batts are stuffed in place and compressed. This defeats the insulative abilities of the insulation when compressed, and hopefully it was installed perpendicular to the joists and should not be compressed.

In one photo it appears the soffits are stuffed with insulation. They should be open and not touching the underside of the roof decking.

Originally Posted by Mainer82

Hi,

We have two bathrooms on the 2nd floor, their fans vent into the soffit on the east side of the house ( I want to correct that at some point).

The side that has the darker spots (all sides do) but the worst is on the northern side of the house. I'm not sure if we have a proper ridge vent, I'm going to get on the roof today and find out.

Here's a link to the photos: https://skydrive.live.com/?cid=b7361...57021E58%21831

My take is that the bath vents are the low hanging fruit. They should not vent into the soffit but directly to outdoors. The bath fans move a great deal of moisture laden air which is something you want to avoid in the attic. The soffit vents are an INTAKE that should provide cold dry air but the bath fans are EXHAUSTING warm moist air. Re-route the bath vents to an area that is not going to be sucked back into the attic.

Next is the roof ridge vent, as you mentioned, make sure it is open and adequately sized. It should be 50% of the total attic ventilation required with the other 50% from functioning soffit vents. Intake should match the exhaust fairly closely and all should be open and functional (i.e. not blocked by insulation, tar paper, etc.)

Next is air sealing around the ceiling/wall penetrations to the attic and the need for a continuous vapor barrier.

Don't forget to seal around the attic access door/hatch/ladder.

Good luck.

If you are running a humidifier, that may be your problem with the moisture collecting on the roof deck. If your furnace has a humidifier built into it, the humidifier attached to the furnace may be the cause of the moisture collecting on the roof deck.

Hello Mainer82-

Based on the photos, the mould is primarily Cladosporium on the OSB with a smattering of Penicillium / Aspergillus on a couple of the dimensional timbers. The growth pattern indicates the moisture source is due exclusively to condensation and not a leak, per se.

I agree with each of the above posters except the notion of remediation. I cannot think of any rational reason to remove the mould, and there can be no good rationale for the application of either bleach or fungicide (in fact, the application of some of the fungicides on the market could result in a explosion of wood rotting fungus that could ultimately compromise the structural integrity of the roof).

If future buyers are concerned about the presence of the mould in the attic, it would be a LOT cheaper to hire a legitimate Microbiologist or Industrial Hygienist to put the situation into perspective than to engage in nonsensical mould “removal.� (The mould is never removed, just displaced, and if the work is done by a “mould remediation company� the work typically increases the mould loading in the structure).

Food for thought.

CaoimhÃ*n P. Connell
Forensic Industrial Hygienist
Forensic Applications Consulting Technologies, Inc. - Home

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG

In my opinion there is not enough mould present to worry about removal/clean up.

Mitigate the moisture sources tout suite.

Originally Posted by Jim Luttrall

My take is that the bath vents are the low hanging fruit. They should not vent into the soffit but directly to outdoors. The bath fans move a great deal of moisture laden air which is something you want to avoid in the attic. The soffit vents are an INTAKE that should provide cold dry air but the bath fans are EXHAUSTING warm moist air. Re-route the bath vents to an area that is not going to be sucked back into the attic.

Next is the roof ridge vent, as you mentioned, make sure it is open and adequately sized. It should be 50% of the total attic ventilation required with the other 50% from functioning soffit vents. Intake should match the exhaust fairly closely and all should be open and functional (i.e. not blocked by insulation, tar paper, etc.)

Next is air sealing around the ceiling/wall penetrations to the attic and the need for a continuous vapor barrier.

Don't forget to seal around the attic access door/hatch/ladder.

Good luck.

The bath fans exhausting into the soffit caught my eyes too. They way you write it makes it sound like they terminate inside the soffit, if that’s the case the moist air will blow right back into the attic. WI requires exhausts to terminate to the exterior (outside) of the structure, and if you vent out the soffit there should be 2’-0� of solid soffit on either side of the termination point to prevent the moist air blowing out from being drawn right back in through the vented soffit area.

Another issue you want to look for is lack of ridge venting. You mention a hip roof and those can lack ridge venting in a hurry. I’ve seen some hips with just 3 feet of ridge venting, far from what is needed. If the house is a long skinny rectangular shape probably not a problem, but if it’s more of a square shape probably a problem.

From the pictures it appears you have ridge venting. How does that work in the land of snow? You need better ventilation to get the moisture out. Those bath vents are pumping into the attic, moisture from those hot showers and its conensating on the cold nail heads? The other guy's got it right.

Hi everyone, I appreciate your responses. I had someone that workings on roofs take a look in our attic and his opinion was of yours, the attic does not have enough circulation as far as the venting outside goes. He suggested to install two roof vents to help with the movement, the soffit baffles are working fine it's that the ridge vent isn't enough. He believes that the spots are mildew and will go away after the venting is fixed.

Our 2nd story bathrooms are on the front side of the house, I asked him to install two vents for the exhaust fans; he suggested to put the vents on the back side of the house. I'm concerned that it would be a bit of a distance for the air to travel from the fan to the exterior if we did that. It could be that I don't know a lot about this but I was under the assumption that the fans should bent straight up?

Is there a reason why he wants to go to the back of the home vs. the shortest distance? Manufacturers will put a limit on their vent piping and some other restrictions, such as number of elbows. Not sure how picky bath fan manufacturers get, but the farther you go the less you actually vent due to turbulence building up in the pipe. The shortest distance with the fewest elbows is usually the best route.

His reason that it would look better to not see them from the front but i don't think it will bother me, I just want them vented correctly.

I was thinking soffit vents, but if you are O.K. with roof vents, that's fine, but you might want to consider resale as others might think it's funny looking or ugly.

Originally Posted by Mike Kleisch

I was thinking soffit vents, but if you are O.K. with roof vents, that's fine, but you might want to consider resale as others might think it's funny looking or ugly.

I'm confused now... the current set up is that the bathroom fan vents into the soffit. I want that corrected.

My last question was is having too many bends, etc bad for the venting?

If you look at this photo, the small window above the front porch is one bathroom, the other bathroom is behind it, both vents would have to be on front or the left side of the roof.

If it's in the left side, the pipe would have 3-4 bends in it vs 1 if it were to be vented on the front.


Edit: Also, for a climate that sees a lot of snow, what type of roof went is recommended?

Esthetically the vent would be better on the side roof.
Just make sure the vent piping is metal ducting, seams sealed, and not the accordian type plastic or aluminum type. It should also be insulated with a fibreglass sleeve.

Also keep in mind a roof vent and its flap could be prone to wind wash resulting in the vent hood flap clattering in the wind.