Indoor Air Quality/cellulose insulation concerns



I am having some last second concerns about installing cellulose Insulation (Green Fiber) in my home.  I have read that sometimes there are issues with smells, allergic reactions to chemicals added to this type of insulation, and it can be very costly to remove cellulose when retro-fitted into walls if problems occur health issue, infestation, mold/wetness, improper installation, etc. Are these legitimate and current concerns with homeowners?

Here are the details:
Dutch Colonial:  built early 1930s, approx. 1625 sq. feet

Attic:  all floor joists filled to their height with fiberglass batts (more than 10+ years ago). It looks to be in good condition from the attic hatch door but has never been inspected throughout. No floor (can some boards be put down after installation??) New roof, soffit vents, ridge vent installed 2 years ago. One gable vent and one window remain open at each end of the attic, although Ive been told they should be covered and closed. Suggested to add R10-12 unrestricted settled cellulose.

Walls:  minimal to possibly no insulation (plaster walls) with possibly some knob and tube wiring present. Dense pack cellulose suggested.

Right now, I am more interested in the attic insulation than the wall insulation because of the invasive work involved with the walls but want to do both if my concerns are not valid.

Can you comment on this and also instruct on proper installation technique and common mistakes or issues often overlooked? Any detailed help would be additionally appreciated also.

Thank you.

ANSWER: Hi Nick,

That an interesting topic that you have raised, so I'll try to break it down somewhat, and if I overlook anything, then please let me know.

As far as odor & allergic reactions, that would depend mainly on your/your family's sensitivity with VOC's. With Stabilized Cellulose, there are chemicals that are added for fire retention proposes, and not intended per say, but those chemicals kill whatever rodents that may chew on it. So there are some benefits in that regards. As far as mold goes, that would only occur if it got wet, and that would only happen if the roof leaked or if the attic area was subject to high humidity levels that eventually condensed. In saying that, make sure all bathroom exhaust vents do exhaust outside & not inside your attic, as I have seen many times in the past.

Now Stabilized Cellulose & Fiberglass Batt Insulation have similar thermal resistance (R-value) that averages to about 3.5 per inch for each. Now just as a side note, if you are concerned about chemicals & odors, fiberglass has formaldehyde in it. But as a side by side comparison, they have similar R-values. The real difference is the time they hold back heat transfer. Fiberglass is very airy, so it allows heat transfer relatively quickly, while stabilized cellulose is more dense thus not having as much air to get heated (heat convection). And if you do add stabilized cellulose on top of the fiberglass batts, then calculate that the weight of the cellulose will press on the batts, thus lowering it's overall R-value, but increasing it's R-value per inch.

Generally what is suggested is to remove what ever insulation is up there, and have @ 1"-2" of foam insulation sprayed on the attic floor joists. This is mainly for infiltration purposes (air barrier) to keep the conditioned space of your home separate from the unconditioned space of your attic, then add the stabilized cellulose on top. But that also depends on how much you planning to invest to do this (monetarily & time wise).

And yes flooring can be added, just remember that when compressed the overall R-value will for example, an attic at R-49 may be reduce down to @ R-32 overall in the locations a pathway or area where plywood is added. So just some things to consider.

Now if there are soffit vents & a ridge vent, then the gable should be sealed closed & the window closed & the glass blocked to prevent sunlight getting in. Something that you may want to consider is installing solar attic exhaust rooftop vents, and with your size house, you'd need 2 of them. Depending on the model, they together would remove 800 - 1500 cfm of air per hour...resulting in a summer attic that can up to 150, down to 100, which lessens the load on your cooling equipment. Just a thought.

Now regarding walls, generally holes are drilled and the insulation is pumped in. The downside, is when repairs have to be done, then it gets messy real quick. Netting is ideal, but that would mean ripping out all the plaster, tacking up netting (same material underneath furniture, like sofas), pumping in the insulation, and sheet rock & paint. So that again depends on what you are willing to invest. So focusing on the attic is definitely more crucial. And when you get that under control, you may not have to do any thing with the walls. That would more than likely just be done, because you just want to, not because you have to.

Now if your home is built over a crawlspace, then infiltration issues may result from the attic becoming more insulated, especially if you seal it (spray foam). So that may or may not apply to your situation...just throwing it out there, so you can prepare better.

Overall, like any type of work...craftsmanship is key. The product is the product. A good product can still be installed wrong, and not perform correctly. So as long as you have competent professionals, then you shouldn't have any issues.

So Nick, I hope that this helps you...and if you have any additional questions then feel free to ask me. And remember to get references from any companies you are entertaining to use.

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Thank you so much for the well thought out and detailed answers, I really appreciate it. The work is being done tomorrow so if you can help me with some additional questions I would, again, really appreciate it.

1.   One of my biggest concerns I neglected to include in my question is the issue of the house being sealed too tight (stale air, possible backdraft problems -  gas steam boiler and hot water tank, etc.), hence part of my initial reluctance to doing the wall insulation. Can you comment and/or advise on that topic?

2.   What is stabilized cellulose? Is that the product that is mixed with water before being blown in? Is that better than using dry cellulose?

3.   Prior to installing the new roof the chimney flashing was in terrible condition for many years. I suspect water dripped down into the attic onto the fiberglass. I can see water marks on the attic wall. How does that damage the integrity of the fiberglass? Does it need to be replaced before the blown cellulose is installed? Does it dry out so I can just leave it alone?

4.   Which is desirable rapid heat transfer (fiberglass) or heat convection (cellulose)?

5.   I dont understand why an attic exhaust rooftop vent should be considered? Doesnt the ridge vent (continuous across whole roof) handle all this? The contractor is suggesting installing one roof vent (not solar) 865 small (.4 sq. ft NFV). Im not thrilled about cutting holes in a new roof, is there any better alternative?

6.   What does infiltration issues mean? I have a concrete basement and only a 16 x 7 portion of it is a dirt crawlspace located directly under a kitchen expansion. A 6ml poly is being put down over the dirt.

Hi Nick,

1st let me thank you for your rating...I really appreciate that.

Now moving forward with your additional questions....

1. There's a motto that is generally used in tight, ventilate right. Most contractors got the 1st part down's the 2nd part (ventilation) that seems to be lacking most of the time. Even in HVAC, the V part (stands for ventilation) is often overlooked, or not educated on very much. But anyways, backdrafting, stuffiness, stale air are all symptoms of not having enough fresh air make up, which should include proper exhausting. Insulation doesn't seal unless it's sprayed in foam, otherwise it's not an air barrier, primarily heat resistive. Granted the more dense the material, obviously will more slow down air flow -vs- fluffier material.

2. Yes, stabilized cellulose is sprayed in damp, and generally holds in place better than dry cellulose. Dry tends to fall & settle more quickly, sometimes leaving peaks & valleys. And stabilized is less dusty when intentionally spraying it in, since it's damp...dust doesn't linger in the air and fall wherever.

3. Once any type of insulation get wet, it basically becomes useless, especially with fiberglass, since it sort of melts away. I'll use an analogy and compare pink fiberglass insulation to pink cotton candy (you'll never look at cotton candy the same way again, lol!). Both look eerily the same...and when you put your wet tongue on your cotton candy, it starts dissolving. That's what water does to fiberglass. So yes, it should be replaced, but then make sure that the leaks have been resolved...don't ever assume anything.

4. Between the two, you'd want heat convection. Think about the sun beating down on your roof in the summer time. A typical attic can exceed 150 and whatever type of insulation installed, will determine how fast or how slow it takes for heat transfer to migrate into your conditioned space of your home. And if you didn't know, the laws of thermal dynamics states that there is no such thing as cold...only heat & less heat, and heat is attracted to less heat like a magnet is to steel. And the opposite is true in winter...heat wants to leave your home and go outside to where there is less heat. Fiberglass is better than nothing by far, but next to denser products, such as cellulose, then it doesn't even compare.

5. That is purely optional...but the reason I bring it up is to assist with keeping the attic cooler in the summer. A ridge vent is great...all houses should have them, but it doesn't circulate air, it only naturally drafts warm air slowly out. An attic exhaust fan would accelerate the process by actually pulling in the air from the soffits and up an out, dragging the hotter attic air with it. The closer you can get to 1500 cfm of air movement per hour the better, but no less than 800 cfm per hour. The reason I mentioned solar was to take advantage of "free" electricity from the sun, and not having to run wires, and raise your electric load.

6. Infiltraion/Exfiltration: Think of infiltrate...something that invades & think of exfiltrate...something that escapes. Now think of air filtration a filter works per say. So in say that...Infiltration is exterior air that's pulled into your home, and most comes through your attic & crawlspace, pulling in whatever dust, mold, etc in with it. Usually with the help of a leaky duct system, which is past your air filter. By the time it reached the conditioned space of your home that air gets mostly filtrated by the 3 largest filters in your home before it ever reaches the actual air filter...your carpeting, your furniture, and your lungs. This is a sign of a very loose house. With Exfiltration...that's air escaping the house, generally because it's positively pressurized against the more negative exterior, and seeps or pushed out wherever it can. This is a sign of a very tight house, which again points to stuffiness, stale air, etc. To note: just make sure that the poly is at 100% ground coverage up the walls @ 3"-6" above the grade of your land. And that any crawlspace vents are permanently closed, sealed, & insulated.

Nick, I do hope that this helps, and if you have any more questions or concerns, feel free to let me know.

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TJ Nichols


Hello, I'd be glad to answer your questions on IAQ & other related issues!


My approach is to treat the home as one system with individual working parts. Think (TEAMWORK). When one or more areas (PLAYERS) are failing or bad, it affects the whole system (TEAM) to operate less efficiently. I aim to address the problem, not just the symptoms, to offer better solution options.

High School Grad (06/1991)(VA) EPA licensed & certified in Types I & II Refrigeration (04/1997)(MD)

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Have served tens of thousands of customers over the course of my career

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