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Please help — I have mold in my attic

MartyPfeif | Posted in General Questions on

2 yrs ago I had a 1940’s three season cabin converted to year round living. This week I found mold in the attic, and lots of it! Let me start by describing the conditions of the attic.
1 no air sealing at all
2 shake and rake R19 insulation in floor and batting against inside walls
3 no vapor barrier
4 I have a ridge vent, but no venting in the gables. I tried to drill a whole to get more ventilation, but I couldn’t get access to the outside by drilling from the attic. Please see picture if helpful.
5 the bathroom vent was vented out a side wall, 2 ft above the fan, and attached with duct tape. It had fallen off. When? I assume I have been venting directly into the insulation for 2 years.
I’m spraying the mold with bleach, and have ordered RMR 80 mold remover. I have removed 12×5 ft section of insulation, and I am in the process of air sealing this section. Can I reuse any of this?
Since I have to go through all of this work I would like to make the space more usable. Either storage, or possibly as a loft. The house is only 600 square feet. It has vaulted ceilings everywhere but the bedroom and bathroom. I have no idea if mold is growing in this part of the roof.
I plan to hire a new contractor, but this time I want to know what should be done, instead of blindly trusting that they will do the job correctly. I’m looking for any advice that will help me be a better informed consumer.
Thank you,

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  1. GBA Editor
    Martin Holladay | | #1

    The most likely cause of the mold is air leaks in your ceiling. These air leaks allow humid interior air (conditioned air) to enter your attic. The moisture in the air condenses on cold attic surfaces, encouraging mold growth.

    The ridge vent is making things worse: by depressurizing your attic, the ridge vent is helping to pull air through your ceiling cracks, thereby adding more moisture to your attic.

    The solution is to temporarily move the insulation on your attic floor so that you can seal the air leaks. Here is a link to an article that describes the required work: Air Sealing an Attic.

  2. MartyPfeif | | #2

    Thank you Martin. I have bought seven cans of great stuff to start. I read that if you completely air seal an attic a moisture barrier is not necessary. Do you recommend a moisture barrier? Could it cause problems?Is it even possible to fully air seal an old house like mine?

  3. GBA Editor
    Martin Holladay | | #3

    Q. "I read that if you completely air seal an attic, a moisture barrier is not necessary. Do you recommend a moisture barrier?"

    A. I'm not sure what you mean by a "moisture barrier." Are you thinking of a vapor barrier (like polyethylene) on the interior side of the insulation? If that's what you are thinking about, it's unnecessary. Very little moisture enters your attic by diffusion. In other words, this is an air leakage problem, not a water vapor diffusion problem. The moisture is piggybacking on exfiltrating air -- it's not diffusing through your drywall.

    Q. "Could it cause problems?"

    A. If you have an interior vapor barrier (polyethylene), it won't cause any problems.

    Q. "Is it even possible to fully air seal an old house like mine?"

    A. It would probably be difficult to achieve zero air leakage. But you can certainly cut down on the air leakage, and make enough of a difference to solve your mold problem.

  4. ohioandy | | #4

    Marty, tough problem, but you can beat the mold problem and in the process make your house way more efficient.

    As you move the insulation out of the way and airseal the cracks, you'll find that spray foam in a can is useful for big obvious leaks like around ceiling lights and sometimes drywall cracks, but you'll typically use way more caulk which is easier to tool into place. Look for major sources of heated air entering the attic, such as around the vent fans, kitchen cupboard bulkheads, heating ducts, plumbing. And if any insulation is obviously wet or moldy, throw it away. Misting it with bleach won't fix the problem; may make it worse,

    And, you said this: "Since I have to go through all of this work I would like to make the space more usable. Either storage, or possibly as a loft." That's Yosemite Sam shooting himself in BOTH feet. A usable attic is a troubled attic. With sufficient insulation, an attic is a terrible place to store stuff--dusty, hot, accessible only through a very tightly sealed door. As for the loft idea, you'd have to completely change how the space is insulated and airsealed; now the roof becomes your thermal and air barrier, which can be a huge challenge in an old building.

  5. KeithH | | #5

    A few suggestions:
    - Get a mask for handling old fiberglass! That stuff is nasty and maybe dangerous. Don't get it in your living space for sure.
    - An handyman worth his salt should be able to easily add gable vents if you have a gable roof and you want gable vents. If you have a hip roof, well that's different.
    - If you are going to do a lot of foam air sealing, get a pro style gun and the pro style cans. The consumer cans are terrible for applying foam and dry up fast. You can also get a super long gun if you want for reaching under the roof. A properly stored pro can on a pro gun lasts months.
    - I know everyone says caulk but I've found that caulk can shrink. Foam shrinks too but is easier to apply in generous quantities.
    - You should be aware of building tapes like Tescon Vana or Siga Wigluv though you likely won't need them.
    - Insulation: It costs more but I personally find Roxul Comfortbatt radically easier to work with compared to fiberglass. Unfortunately if you have 2x6 ceiling rafters, it's likely a special order (big boxes have 2x4 in stock typically for roxul but not 2x4). If you decide to bin a bunch of insulation, you might look into that option instead of more fiberglass, depending on your budget and preferences. YMMV, but I've never seen Roxul grow mold, even test pieces left outside for a winter. It's radically more moisture resistant than fiberglass. Though once you solve your moisture issue it shouldn't t matter much.
    - Bathroom fan venting: Proper 4" ducting, duct screws, and hvac tape are affordable and sold at all big box stores. Get rid of any flex duct and unsecured ducting. Screw and tape the seams. You could also, depending on the location of the van, consider venting it upwards and then out to the gable end of the attic if for some reason you can't repair your sidewall vent setup. If you are soffit venting, I'd switch to venting up into the attic and duct it all the way to the exterior wall of the attic (again, assuming gable roof).

    Good luck!

  6. MartyPfeif | | #6

    Thanks Keith, Andy and again Martin. You have provided me with some helpful information, but of coarse it leaves me with some more questions. Please don't think that I am an ignorant person, but I need clarity on a few more points.
    After running the bathroom fan for a couple of hours yesterday, I noticed ice and condensation had formed on the flex duct I had secured. If I insulate this duct will that take care of it? I have no problem switching to the metal duct, but I want to concentrate on air sealing, and come back to that once this is done.
    I'm using great seal foam on the seams, pipes, and other random holes. Do I need to air seal the outer support beam on each end?
    The seams on the ceiling are taped, and I am just foaming over it. Is this ok?
    The old ceiling was not removed over the bathroom and bedroom I have no drywall in the house. It is all car siding. Does this change anything?
    Should I air seal nails coming through the ceiling?
    Unfaced bats of insulation are duct taped to one inner wall, and the other wall has no insulation. Does this matter after I air seal?
    The moisture barrier I plan to use is black 6mm Poly. Is this ok?
    The bleach is working, but my eyes are very itchy, and my cheeks feel irritated. While wearing the N95 respirator the smell of bleach became intolerable. I don't think I had the mask sealed, and the fumes were trapped under it. I have been fit tested and trained on how to apply the mask, but the 3M mask I purchased at the store was stiff and difficult to mold. I feel like it did more harm than good. Are the fiber glass particles to large to pass through a bandanna? Thanks again for everybody's help. I really appreciate it!!

  7. KeithH | | #7


    First, I'm just a DIYer so balance that vs other responses.

    Flex duct for your fan: maybe it works for some people but given your problems, I'd ditch it. FYI, if you have a local used building yard, you can get metal ducting pieces for pennies on the dollar.

    Seam in the ceiling: in paneling? I guess foam works. So would caulk. So would tape.

    Nails in ceiling: I don't think you need to foam those.

    Batts of insulation: I don't know what you mean. I'd insulate everything after you have air sealed. You don't need to duct tape the batts. I guess I don't understand what's happening. Picture?

    Moisture barrier?? Where are you planning to put 6mm poly? From what I read, I'm not seeing where a vapor barrier is a good idea. Don't put that on top of your insulation: you'll trap warm moist air from inside your house in the insulation.

    Bleach: I agree with the previous commentator that the bleach is likely not helping anything and you could harm yourself. If the insulation is that moldy, dump it. If it isn't, solve the moisture problem. An N95 mask or even an N100 respirator is not protection from chemical exposure. I don't know enough about chemical exposure protection to say what would protect you from bleach but an N95 won't. I suggest you try calling 3M or another vendor of respirators to get assistance with what type of respirator cartridge is needed. Again, I would not continue the bleach.

    Masks: An N95 will reduce your exposure to fiberglass and mold but given the hazards and poor airflow, I'd get more serious about your personal protection. Consider a respirator. Is there anyway to get some airflow so you don't fill the air with mold and fiberglass? A bandana is useless.

  8. GBA Editor
    Martin Holladay | | #8

    No one on this web site told you to use bleach. Skip the bleach. If you need to clean up mold, ordinary soap and water (for example, dish detergent or laundry detergent) is all you need -- plus some way of keeping everything dry.

    You wrote, "The old ceiling was not removed over the bathroom and bedroom I have no drywall in the house. It is all car siding. Does this change anything?"

    The term "car siding" is a regional term -- in most parts of the country, it leaves people scratching their heads. As far as I know, you are talking about tongue-and-groove boards.

    Answer: Yes, this changes everything -- and it explains your mold problem. Tongue-and-groove boards do nothing to stop air flow. Air can move through tongue-and-groove boards like window screen. That's why your attic is so wet.

    You absolutely need an air barrier to correct this problem. The best type of air barrier for a ceiling is ordinary drywall.

    The easiest approach is to install drywall on the interior side of the tongue-and-groove boards. Of course, that means you won't see the boards.

    If you love the boards, and want them to be visible, you can try to remove them carefully so that they can be re-installed later. As long as they weren't installed with ring-shank nails, this is probably doable.

    After the boards are removed, install drywall with taped joints. Then re-install the boards on the interior side of the drywall (assuming you like the look).

  9. MartyPfeif | | #9

    The vaulted portion of my ceiling was insulated with a moisture barrier. Above the bedroom and bathroom the old ceiling was left in place. It was made of a durable cardboard material ( see pic).
    The tongue and grove wall over my kitchen cabinets were not insulated at all. the walls in the living room were insulated, but very poorly. I haven't taken any of that down yet to see if a moisture barrier was used, but there is large gaps in the corner seem, and I can see the attic light when turned on.
    Using bleach to clean the mold was strictly my idea. I took the day off, and my itchy , watery eyes are much better. It looks like the bleach is working, but I did order a product called RMR-80. Has anybody used it? A friend has offered to pressure wash the attic once I get the insulation out, so I probably will go this route unless there is a reason this is not advised. Thank you all for your advice and concern for my health!

  10. user-2310254 | | #10

    I think you are asking for trouble if you pressure wash the attic. If you air seal the leaks, it is likely the mold will dry and become a non-issue.

  11. Expert Member
    MALCOLM TAYLOR | | #11

    I'd go further than Steve: pressure washing the attic is an insane idea.

  12. MartyPfeif | | #12

    I will forget the pressure washer. I honestly thought it sounded like a bad Idea, but desperate times call for desperate measures.
    Steve Knapp- I was kinda thinking along your lines. Take away the environment that caused it. But what about spores. Spores can lay dormant, and wait for conditions to change. That is why this is so important to me that I get it right. I really appreciate everybody's inputHere is my plan
    1 lay moisture barrier on ceiling (attic floor) after removing all insulation
    2 Air seal, air seal. air seal
    3 install gable vents ( roof ridge already in place)
    4 re-insulate. I haven't decided if I will reuse what I have, or buy new. I'm leaning towards new moisture resistant insulation.
    A couple of questions:
    1 should I air seal outer walls and roof?
    2 When laying my vapor barrier should I secure it to the outer joist (terminology?) on the outside wall?
    3 For every foot of roof ridge vent how many gable vents should be installed, and should they fill gable space ( what size do I need to buy)?
    4 is it ok to leave the bagged insulation up there for now? Some of the bags formed condensation on the outside.

  13. ohioandy | | #13

    Hey Marty, I think you're missing the basic point, and your plan is too complicated. Back in comment #3, Martin surmised that your main problem is air infiltration--that is, warm moist air squeezing through cracks into your attic. Then you essentially confirmed this when you mentioned that your ceilings are all carsiding (what most of us understand to be tongue-and-groove boards.) People like the look of a board ceiling, especially in a cabin, but by itself it's not compatible with a heated house. It MUST have an air barrier added. Draping sheet plastic over the joists in the attic is an awkward solution at best--hard to seal and prone to compromise. Plus, you DON'T NEED any kind of "vapor" or "moisture" barrier on your ceiling--just an air barrier, for reasons that Martin also discussed.

    So it may be a tough decision, but really your only workable solution is to put up drywall on the ceiling, either just covering up the boards, or tear off the boards and reinstall them after the drywall is taped (although FWIW this introduces a thousand nail holes into the drywall...)

    Don't worry about mold spores. Neither chemical baths nor outlandish cleaning will get rid of them all. If your attic is dry, they will remain dormant and harmless.

    Don't worry about attic ventilation, or airsealing the roof. If you have a properly sealed ceiling and enough insulation, your attic will be fine. Without soffit vents, gable and ridge venting is barely functional anyway. (This has been discussed often on GBA; do a search.)

    Extricate ALL old insulation that appears moldy. Cheap ol' blown cellulose is all you need, IF your ceiling air barrier is good.

  14. Expert Member
    MALCOLM TAYLOR | | #14

    I'd suggest:

    -Air-seal the ceiling. Don't worry about the roof or walls.

    -Remove all moldy insulation and replace it.

    -Ventilate the attic properly.

    -Clean up the existing mold and encapsulate the spores with a product like Concrobium.

  15. Jon_R | | #15

    Consider having a professional apply a couple inches of spray foam to the entire attic floor and then cover with cellulose. Have the entire house tested & sealed for air tightness. Install wireless humidity sensors (interior and attic) to verify that everything remains OK (for example, a roof leak will cause a spike in attic humidity).

    If you are really concerned about inactive mold spores, consider soda or dry ice blasting followed by spray painting with mildew resistant paint.

  16. MartyPfeif | | #16

    I want to thank everybody for their time, knowledge and patience. I feel empowered to hire a new contractor, and ask the right questions have the job done correctly this time around.
    I think it would be more cost efficient to air seal with foam, rather than install drywall. This is especially true in the vaulted portion of my ceiling. A teardown would entail all new boards since my builder chose to attach them with long staples that are impossible to remove without damaging the board.
    I am going to look into the wireless humidity detector, and the other product recommendations are very helpful as well.
    Kindest Regards,
    Marty Pfeif

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