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Mixing cellulose insulation and whole-house fan

molyneux51 | Posted in GBA Pro Help on

Had 6″ blown cellulose added to our small 440-sf attic in spring 2010 (entire upstairs is 900 sf and balance of area beyond 440 sf is cathedral ceiling) … The contractor installed a rigid insulation dam around the small whole-house fan (Tamarack 1600 Gold with 1150 cfm on low speed, we only use low and never high due to fan noise) …

Winter 2011, we had a shut-down of the attic venting system due to airborne cellulose stirred up the the whole house fan migrating to the Cobra mesh ridge vent and completely clogging the mesh .. resultant mess with mold and condensation damage ended up costing $25,000 to rip out all 2nd floor ceilings, remediate the mold, engineer $ fees, demo insulation systems in attic and cathedral ceilings, and re-do entire upper floor of house with closed cell spray foam and all new drywall …

I am trying to get industry feedback from professionals who have knwoledge of dangers of mixing cellulose and whole-house fans .. industry links, websites, anything that discuss this issue would be great. Thanks ..

Please also email me at [email protected] in addition to posting here in case I miss your post at GBA website …

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  1. GBA Editor
    Martin Holladay | | #1

    I have never heard of a whole-house fan blowing cellulose insulation into a ridge vent. My first question would be, how high was the insulation dam around the fan?

    The second issue is more pertinent: it is very unlikely that a clogged ridge vent would cause your second-floor ceilings to get moldy, so I'm guessing that you are blaming a humidity and mold problem in your house on a ridge vent problem -- and that the ridge vent is an innocent bystander.

    There is no way that GBA readers can get to the bottom of this issue by reading your description of what happened. We need much more information, and only a site visit could nail down the pertinent facts.

  2. molyneux51 | | #2

    The Cobra mesh ridge vent was completely blocked by airbone cellulose that migrated to the ridge, either by eave soffit wind events or the whole house fan ... house is 34' 6" long and the entire length was contaminated, most of it so badly that there was about 1" depth of clogging cellulose adhered and imbedded into the ridge mesh ... I discount eave soffit wind events, as the amount of clogging was too severe ... it most definitely was the clogged mesh ridge vent that shut down the attic ventilation system ... our own engineer confirmed this by inspection and by written opinion, the mold remediation company concurred by written opinion, and our home insurance independent engineer who inspected also concurred by written opinion ... I have found a compnany in Colorado (Applegate) online who admitted to me they had seen this problem on installations and now install a "loose fill insulation cover" mesh over the top of cellulose in houses they install in that have whole house fans .. but one website does not make substantive proof in our legal beef with the insulation company ... the rigid insulation dam is about 10" above the top of the floor joists (just an educated guess, I am not going to unload the closet and climb back up there to measure it) ... so the installed 6" layer of cellulose on top of the original joist deep fiberglass batt would have come to within 4" of the top of the rigid insulation dam ... we discovered the problem the week after Christmas 2011, when a wet spot began appearing on the northwest side cathedral ceiling in the bathroom at the ceiling to wall joint ... originally, we all thought it was an exterior leak and the insurance company instructed me to cut out the wet sheetrock to aid drying and tarp over the roof to stop further infiltration ... after the roof was tarped over, the wetness continued with actual dripping from the undersicde of the roof sheathing and I then realized the problem was internally created .. so I popped the hatch into the attic for a look ... and the entire roof plane of the attic throughout the house was dripping wet with condensation and the top 2" of cellulose was dampened ... basically it was raining inside the attic ... mold everywhere ... and the ridge mesh was severely clogged with cellulose .. I guarantee no one climbed up into the attic, grabbed handfuls of cellulose, and stuffed it into the ridge mesh from beneath .. keep in mind that the house was built in 1989 and the original Cellwood Triple 4 soffit vents and Cobra ridge mesh worked just fine for 22 years until the year after the cellulose was blown in .. and the whole house fan was installed in 2005, predating the cellulose by 5 years with no condensation or mold problems ... the cellulose and whole house fan interacted badly together and I can find scant information about this issue online, but hope someone has more websites, links, industry information etc I can use ... thanks.

  3. GBA Editor
    Martin Holladay | | #3

    Thanks for the further information. The issue you raise -- the possibility that a whole-house fan could interact with cellulose insulation, resulting in a clogged ridge vent -- is certainly interesting, and I am interested in hearing whether any other GBA readers have information on the topic to share.

    That said, I can't imagine that your house could have ended up with moldy ceilings unless (a) your interior moisture levels were very high, and (b) that fact was disguised by massive air leaks through your ceiling into your attic, a situation that resulted in the entry of lots of outdoor air that masked your humidity problem.

  4. homedesign | | #4

    The clogged vents may have contributed to the problem(s)... but are likely not the only factor.
    Since the "House is a System" it is also possible that merely adding the cellulose... considerably changed the SYSTEM.
    Causing the attic, the underside of the roof deck and the top of the insulation to be much colder (and wetter) than ever before.

  5. molyneux51 | | #5

    cheesh guys, please quit parsing the issue ... I have 2 registered professional engineers and a mold abatement expert that all say that the whole house fan caused the cellulose to become airborne and the airborne cellulose clogged the ridge mesh at the attic ridge line ... there is zero other way for the entire length of the ridge mesh to become packed with cellulose other than by airbornee cellulose, thereby shutting down the attic ventilation system ... what I need is any available industry backup that specifically discusses interaction between cellulose and whole house fans ... all these other guesses do not add to the discussion, thanks.

  6. GBA Editor
    Martin Holladay | | #6

    I don't think anyone is doubting that the ridge vent is clogged with cellulose due to the operation of the fan.

    But in a well built house, a clogged ridge vent won't cause the kind of damage you describe. Something else must have been seriously wrong with your house to cause the damage you describe.

  7. molyneux51 | | #7

    Warmer air from below slowly leaking into attic (does this even with fiberglass and cellulose insulation system installed and minimal air sealing issues from below) + cold air inlet from eave soffit vents + no ventilation outlet at ridge = condensation from warm air hitting cole air builds up inside the attic and with weather changes, increasing condensation has nowhere to go ... batt and cellulose remove and clsoed cell spray foam installed along with new ridge mesh, whole house fan remains and no problems ...

  8. GBA Editor
    Martin Holladay | | #8

    Two factors are likely: very high indoor humidity levels and excessive air leakage through your ceiling.

  9. molyneux51 | | #9

    No ... engineer reports stressed minimal air leakage from below from bad sealing per se and indoor humidity no higher than 35% ... plus fiberglass insulation beneath cellulose was dry, only top inch or two of cellulose was damp from condensation dripping down .... no mold or dampness on the cold attic floor framing, would expect to see that if air leaking from below, at least in the upper layers area of the fiberglass ... or you would have expected this to have been an issue before the cellulose was installed in 2010, as even more warm air would have leaked thru just the fiberglass insulation by itself and condensation would have been an issue from 1989 to 2010 ... all mold was contained on underside of roof sheathing and exposed attic framing .... again, in house conditions had not changed from 1989 thru 2010 and was not an issue prior to 2010 ... if the ridge mesh is blocked, warm air cannot escape and continues to build up inside, condensing and condesning as warm air meets the cold attic air ... once ventilation was restored by roofer installing a new ridge mesh but before any insulation or demo was done or any mold remediation done, attic began drying again due to positive air flow in eave soffit vents and out the new ridge mesh ...DOES ANYONE KNOW ANY WEB SOURCES DISCUSSING CELLULOSE INSULATION INTERACTION WITH WHOLE HOUSE FANS??? ... THANKS.

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