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Poor attic ventilation, a.k.a. mold on rafters

kkdibba | Posted in GBA Pro Help on

Hello all,
Here are the basic details:

– I have a 23 year old 2-story frame house in the mid-Atlantic region (Zone 5). The roof was replaced last year, and there is a ridge vent, soffit vents at intervals and baffles inside the attic to allow unimpeded air flow into the attic.
– The bathroom exhaust fans are vented off to side camp vent on the side off the house. Though the fans seem to be running, I have a serious suspicion that they aren’t actually pulling in anything.
– The attic space had about R-36 to R-38 of batted and blown in insulation put in by the previous owner and I intended to have someone come by and blow in insulation to bring it up to R-49.

I called in a local contractor to come by & do a full blower audit test and recommend stuff to improve the insulation and recommend other things to improve efficiency. When I went up with him, I noted signs of mold growth in the roof rafters in the attic. There is no sign of water or smell – so it is still in the initial stages.

Contractor recommendations:
– Seal penetrations in attic space
– pull back insulation from soffits and reposition baffles to allow air up to the attic to dry out mold.
– Add can light cover to recessed light fixtures
– Build Insulated Attic Hatch w/ Removeable Lid
– I had what seemed like 2 cold air return register in my bedroom: 1 near the ceiling seemed to be NOT connected at all – just vented out straight into the open attic space & the 2nd near the floor that was connected. He suggested removing the vent and drywalling it up.
– Extend bath vent to outside including butterfly air control baffle

1. I agree with all of the recommendations he gives EXCEPT for the last one.
o The mold is on the rafter OPPOSITE the bath exhaust fans on the side that faces the setting sun. There seems to be no mold growth in the rafters right around the bath fans. Is it possible the stronger heat of the setting sun can create mold on the rafter if there is enough moisture in the attic but not in the region of the source of the moisture? If I am right re: the non-working of the fans is this a contributing factor as well?
o The bath vents already are vented outside via the side camp vent. Is there any benefit in going through the roof with a butterfly air control baffle?
2. Can return air registers be near the floor? I thought they needed to be up near the ceiling. My concern is whether the upper register needs proper ducting to do the job right as opposed to drywalling it off and have some other issue crop up.
3. When I look up straight at my ridge vent, I see a blue mesh along the length. Is this normal? The roof replacement was the last change done, so there is good reason to suspect that could be the reason for the poor attic insulation.

I have called 3 insulation guys to comment on these issues. Only 1 did a blower test and recommended the above. The rest were like – not our problem. Call someone else. We just dump insulation The question is who do I call:
– HVAC guy?
– Roofer?
– Mold remediation guy?
– Plumber?

Please help. I’d appreciate any help, because I’d like to get this taken care of and I have just one guys recommendations & estimate (obviously the highest of the lot) and I am at my wits end.


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  1. GBA Editor
    Martin Holladay | | #1

    Your attic is damp. The moisture is coming from the interior of your house, through air leaks in your ceiling.

    The solution is to seal the air leaks in your ceiling. Attic ventilation isn't that important, but it can't hurt.

    Your bathroom exhaust fans should definitely be ducted to the exterior, not to your attic. They may be contributing to your problem. Terminating your bath exhaust ducts to you attic is a code violation and is not recommended by any experts.

    I have no idea what a "side camp vent" is, by the way.

    For more information on this topic, see these two articles:

    Air Sealing an Attic

    All About Attic Venting

    If you want to hire someone to do this work, you should look for a home performance contractor.

  2. kkdibba | | #2

    Thanks for the quick followup. Sorry! I meant "Side wall vent" like in the picture attached below. I see this on my siding right in between the two bathroom areas, & I see silver-foil flexible vent tubing snaking off the two fans in the attic into the side of the house. I'm assuming the fan vent tubing terminate at this side vent on the siding of my house.

    So, the bath fans arent venting into the attic per se - however if the fans arent pulling anything - then what you say is right - the moisture is essentially venting into the attic via leaks.

    However, is the side venting of the fans enough (if I replace the fans) OR should I have the roof-venting with the butterfly air control baffle thingie done as he recommends?

    And am I reading your comment right? The location off the mold on the opposite side of the bath fans isnt significant as long as there is moisture coming up into the attic. Is my guess re: the heat of the setting sun correct then?

    The guy I called in was a home performance contractor. I am just trying to get some more info before I get him to do the job.

    Thanks again for responding.


  3. GBA Editor
    Martin Holladay | | #3

    It's hard to know whether your bath exhaust fans are properly ducted from your description. Rigid duct (for example, 4-inch or 6-inch diameter galvanized ductwork or PVC pipe) is better than corrugated flex duct. Ideally, the bath fans are ducted straight up for about two feet to an elbow, and then slope downwards toward the temination, which is best installed on a gable wall. You want any condensation to drip toward the exterior of your house. This rigid duct should be supported on wires or hangers so that it has no sags.

    The location of mold is often a clue that indicates your most significant ceiling air leak. You might look directly under the moldy area to try to find whether there is a significant leak (an unsealed chase, a large crack, an unsealed soffit) directly under the mold.

  4. kkdibba | | #4

    Perfect. Thanks for the hand-holding. That helps a lot.

    One last remaining question from my original post & I'll be out of your hair...
    "Can return air registers be near the floor? I thought they needed to be up near the ceiling. My concern is if the upper register needs proper ducting as well, to do the job right as opposed to just drywalling it off and have some other issue crop up later."


  5. kkdibba | | #5

    To followup - it could be that one register was for winter (heating) and the other was for summer (cooling) but the cooling vent duct was never connected and left as eseentially a big hole in the wall. Is there any value in having the ductwork done?

  6. GBA Editor
    Martin Holladay | | #6

    Return air grilles can be located near the floor or near the ceiling; either location works.

    Ideally, every return-air grille is connected to rigid ductwork. However, in some older homes, empty stud bays or joist bays were used to convey return air from the grille to a location near the furnace. Needless to say, this method doesn't work very well.

    If you remove the grille from the wall, floor, or ceiling where it is located, you should be able to tell whether the grille has a boot, and whether or not the boot is connected to ductwork.

    If the return-air grille is not connected to ductwork, it would be a good idea to have your return-air system inspected by an HVAC contractor. If necessary, new ductwork and new return-air grilles should be installed, either in the same location where they are now, or perhaps in different locations.

  7. kkdibba | | #7

    Great! Thanks for your assistance.

  8. kkdibba | | #8

    So based on your last response, I called in a HVAC contractor (who also advertises in my area as performing energy audit's and affilated to an organisation called Dr EnergySaver). Once he saw the mold, he declined to do the blower test and recommended I call in mold remediation people. He said he'd worked for a mold remediation company before and gave me a number. He said even if the mold spores are killed, the allergans will still be around. I think he was in pure BS mode.

    I have serious doubts about going down that route. As far as I see, there is mold everywhere in our environment and the mold in the attic has had no adverse health effects on anyone at home - and one member of our household is immuno-compromised and even he has not felt any adverse effects either. So far as I can see, the mold remediation folks seem to charge $1000's to come and clean up the effects, and then I have to spend another chunk of money to fix the original moisture issues.
    What do you think? Are my instincts correct.

    So my question is:
    - Do I need to do mold remediation first before doing the attic sealing project? The original "comfort solutions" energy-audit guy indicates that doing the things he recommended (which I listed in Comment#1) will clear the mold problem by itself without specific mold remediation.

    Is this the right way to go?

    Thank you so much for your guidance.

  9. GBA Editor
    Martin Holladay | | #9

    It's hard to know how serious your mold problem is without a site visit, but the opinion of the HVAC contractor who visited your house indicates that your mold infestation may be severe. I haven't been in your attic, so I don't know what's going on up there.

    If you don't trust the opinion of the first contractor who came to your house, you can always get a second opinion.

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