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Cellulose insulation odor

TfMWMX1nC2ZsbO | Posted in General Questions on

I have a question about a recent blow-in cellulose insulation installation on an attic floor.  Briefly, as soon as it was installed there was a strong odor similar to stacks of newspaper sitting on a windowsill in the sun…

Background information:
– Climate Zone 4
– 1970’s ranch house with hip roof
– Hip roof with the continuous ridge vent (~830 sq. in.) and rectangular soffit vents (~950 sq. in.)
– Air handler and supply / returns in attic space.  Sheet metal main trunks with flex duct runs. 
– Seams on trunks were taped and wrapped with R-8.  Connections between flex and trunks were taped.
– ~5.5″ of yellow loose fill fiberglass originally
– ~10″ of cellulose added on top
– ~5″ of cellulose added on top of ductwork per GBA article on buried ducts
– R-1 (i.e. 1/4″) insulation board added around the entire perimeter in lieu of baffles.  I.e. the original fiberglass fills the joist depth and then the R-1 sits on top at the interface between the rafter and ceiling joist
– Can lights had foam insulation boxes installed over them / spray-foamed around the bottom
– Heat pump and air handler approximately 20 years old, so the idea was to use it until it died and then abandon it and re-duct in the unfinished basement (no idea why it wasn’t put their originally!).
– There are three bath fans that terminate in the attic (one is hung adjacent to a “baffle” directly above the soffit vent; the other two have 180 degree turns (i.e. they point back down)).
– The bath fan interface with the ceiling was spray foamed, as were the supply registers.
– Wire runs were spray foamed

The odor is strong when the A/C is running.  My assumption is the flex duct jackets (since they’re old) had little holes (I tried to tape the ones I saw) that are letting the odor in.

If the supply vents are covered and left alone all day, there ends up being a slight odor.  So perhaps some air leakage around the registers at the ceiling or some through the bath fans.  Initially I didn’t think it was the bath vans as I alternated covering the fan and supply on different nights and in the morning the bathroom smelled when the bath fan was covered but not when it was open.  
The smell is noticeable outside the house as well.
The smell seems to be stronger on sunny days (the shingles are black).

The cellulose insulation says up to 85% recycled newsprint, <15% boric acid, <4% calcium sulfate dihydrate, up to 2% amylopectin, <2% distilled mineral oil.  The specs say no odor, and the manufacturer confirmed that when contacted about the odor.  “Must be a chemical mixture imbalance” is what I was told.  They originally said I could walk through the attic with a spray bottle of half water and half vinegar and it’d remove the odor (but they didn’t know why it worked).

So, my questions:
1. Is the odor a health hazard?  I get a headache / tight feeling in my throat after long exposure (we’ve been airing out the house overnight, which obviously introduces a bunch of humidity)
2. Will the odor eventually dissipate?  If so, how long for 10″ of insulation over 1,750s.f.?  
3. Is there anything to expedite the dissipation?
4. Is there anything to mitigate the odor in the interim (e.g. charcoal or something in the supply vents?  spray vinegar / water mixture into supply vents?)?
5. Should I remove and replace the cellulose (to the tune of $10,000 from one insulation contractor)?  
6. Do I leave it / abandon the existing HVAC and get a new system / ducts in the basement?

Thanks for reading this far and for your insight!

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  1. Expert Member
    Akos | | #1

    In the summer time stack effect works in reverse, you get warm air leaking in through the ceiling and cold air out through the bottom of the walls. This means that it will inevitably carry some smell from the attic in. The air handler in the attic is definitely not helping things. Since you mention it is strongest when the air handler runs, most likely culprit is the return air ducting to the unit as well as the filter frame and area around the intake of the air handler. Since the return ducting is under negative pressure when it runs, any air leak there will directly draw in air from the attic. The supply ducts won't create this type of issue since they are under positive pressure.

    I would go and try to seal up the return ducting and air handler intake as much as possible.

    Unfortunately cellulose made from newsprint will smell like newsprint, over time some of the smell will dissipate a bit. As long as it is not mold or chemical smell, there is not much you can do about it.

  2. Robert Opaluch | | #2

    EPA pesticide classification document states that boric acid not considered a health threat to humans, not carcinogenic, but can cause some eye irritation when applying it:
    However it is effective against many insects and a fungicide.

    Using foam board to enclose can lights can be problematic if older style incandescent bulbs are used, since larger wattage incandescents emit significant heat. Only use LED lamps, and firesafe covers are recommended to prevent someone mistakenly using incandescents. Example:

  3. TfMWMX1nC2ZsbO | | #3

    Thank you both for your review and reply.

    The return is a shorter section of sheet metal duct with two grills in the hallway ceiling (although there's a short piece that's just a flat section of sheet metal on top of the joists; I'm not sure what the point of that and associated elbow to the main duct are as there's nothing visible from below). The return is connected to the air handler with a larger diameter flex duct.

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