We don't have many brick homes around here in central Vermont. I recently visited a one-story ranch home that was built with exterior walls of hollow core CMUs (concrete masonry units), a brick exterior and a sheetrocked interior that is strapped to the CMUs, which are filled with vermiculite insulation. I am looking for advice from auditors who have experience with this type of construction. Would you feel comfortable doing a BDT (blower door test) that depressurizes the house? What concerns would you have about this?

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Any chance of asbestos - it is an automatic no thanks

Have you thought about pressurizing the house instead

If the drywall is in good shape, you should have little worries about the 50pa depressurization moving fibres of asbestos through the CMU and the drywall into the house.  You could also do a Pressurization test and eliminate that.

What was the insulation in the attic?  I am assuming not vermiculite since you didn't measure it.  If so then no blower door testing until removed.

Finally, how did you determine the presence of vermiculite in the cores of the CMUs.


In Kansas City about 22% of poured in vermiculite has a trace of asbestos .1%.   Lots of block was made here in past 90 yrs and lots of vermiculite was baked to expand to make insulation.    If you see vermiculite you will also so may see knob and spool wiring with RA covering or rags fiber coating above the 1-2 inch of vermiculite.   How about putting a fire proof netting above the whole mess?   Just thinking?  I have had the attic vacked  and then rewired and then resealed reinsulated  but gets high in labor?

For John N.- The homeowners had the house gutted and renovated. They found vermiculite leaking from a couple of holes in the CMUs. They also believe that the vermiculite can be seen at the top of the CMU walls in the attic. They also told me that there was no vermiculite in the attic and that they installed fiberglass batts. BTW, the house was built in the 1960s.

There is a large, open addition to the main house, so a depressurization test would help find the air leaks, whereas a pressurization test would not help find the leaks.

So, is the plan to just do the addition; fix the holes where the CMUs are leaking the vermiculite and replace with something for R-Value; or something else?

I had a blower door done on my 1979 block home but didn't know I had that in the walls. I must have it, another auditor told me, because my house is now tighter than I expected it to be. 

After the energy audit was complete, I added Icynene under the lid of the roof, 16 SEER Trane variable speed unit, all LED's Energy Star appliances, Low-e windows and door with a thermal front door, and aerosealed my rigid ducts.  I'm in AZ and found my house to be almost too tight so will need to add some fresh air since after showering my house seems humid.  Need to replace my bathroom fans.

Lastly they did not remove the old cellulose, which has been causing quite a smell in my attic even though the attic is now conditioned space.  That will all be vacuumed out next week. 

I had an indoor air test done and all came back fine. 

Jan- If you had a blower door test (BDT) done and there was vermiculite in the hollow cores of the CMUs, then I wonder if any asbestos fibers in the vermiculite could be sucked into the house during the  BDT. That aside, if air sealing work was done, then the BDT should have been repeated to see if fresh air needs to be supplied with mechanical ventilation.

"If you don't test, you guess!" I hate to say that a house is "too tight", but only a BDT will tell you HOW tight and give you a better sense of whether you need mechanical ventilation, or not. If your house seems humid after showering, get an inexpensive digital temperature & relative humidity meter (I recommend Acurite brand). Measure the actual flow of you bath fans, or at least give them the "tissue test". Hold a piece of tissue (or toilet paper) up against the fan (when it is running of course) and it should be sucked toward the fan. If it barely moves or does not move at all, the fan is not vented properly.

As for the cellulose insulation that "has been causing quite a smell", I venture to guess that it smells like ammonia, which is given off when cellulose is treated with ammonium sulfate as a fire retardant. It is an inexpensive fire retardant, but is rather corrosive and gives off fumes when wet or damp.

Hope that helps

The air test was done prior to Aerosealing and tests were fine. No drywall was removed so the vermiculite was encapsulated. 

Great comments about air quality. I'll check the bathroom fans.  

The cellulose is definitely very old and likely the cause of the odor.  Frustrating that it's in my closet!  

Thank you! 

Are the bathroom fans ducted to the outside or into the attic?  

If they exhaust outside,   *Not* into the (now sealed) attic, great.   Replace your bath fans with a new one.  Get an 80 CFM model ( to still move 50 CFM from the bathroom after duct friction losses). Insist on a unit that has a sound rating of  less then 1 Sone.  Some brands have a control module available.  Occupancy, Humidity, Timer.

Repeat the BDT and have the person running the BD calculate the amount of CFM you need to get your mechanical ventilation as required. (ASHRAE 62.2)  You can go to Rick Karg's site Residential Energy Dynamics and do that also.  *But* ask the person running the Blower door to calculate it, before you hire them.  Easy way to judge basic competence and experience.

You can use an exhaust strategy for very little investment now.  Then you can upgrade to a balanced system later (ERV). Your now quiet bath fans can be used to supplement the ERV when you have periods of more intense weather.

BTW:  I grew up in Southern Nevada in a CMU home.  No insulation at all in the walls or attic. Built in 1954. The house we rented before buying, was stick built, no insulation either.  

Thank you John!  That's my plan, swap out the fans first.  Appreciate the advice!   

As a realtor with 2 designations in green building, we still have to rely on others to do the work.  Like most consumer products, i feel as if I need to know more than they do to manage my remodel, etc.  Sometimes that's VERY frustrating.  And this is one of those cases.  It's been great to read these types of issues to understand even further what should have been done, ie removing blown in cellulose when installing Icynene.  Argh!

I would not 100% of the time recommend removing the fibrous insulation on the attic floor with the roof deck is insulated.  I'm not sure from your description that is your odor problem.  I am questioning if your house is tight enough that with no mechanical ventilation, you have created a different problem.  I would work on that first before you remove the insulation and find the problem still there. Either way you have to do the mechanical ventilation.

I would also suggest purchasing the fans and paying a tradesman to install them.  Your home probably has fans with a 3 inch exhaust.  Any quiet fan will have a 4 inch or even a 6 inch exhaust,  The larger exhaust helps lower the sound,  So the installer will be replacing the ducting along with the fan. 

You can check the specifications at HVI.org.   Home Ventilation Institute.  Testing organization on the grounds of Texas A&M at College Station.  Then get the model numbers and look online at the manufacturers website for images and install instructions.  All types of Brands there,  So I would concentrate on a few.  Broan - Panasonic and Fantech are 3 to start with,  

Check in with the company that did your original blower door test to see what they know about the local market.

Good points John. As a contractor, if a client provides a product (such as a bath fan) and asks me to install it, I usually will but with the caveat that I provide NO warranty of any kind.

I am a big fan of the Panasonic Whisper Green fan. You can change the speed (50-80-110 CFM for most common model) and add modules such as motion sensor, two-speed control, night light and humidity control. They are very quiet and are relatively easy to install. Note that for Broan to provide a fan that is almost as quiet, you have to provide a 6" duct, where the Panasonic is <0.3 sones with a 4" duct. If the duct is more than about 10 equivalent feet, you should upsize to 6". If you have to vent out a soffit, use an appropriate soffit vent termination.

I prefer the motion sensor to control the fan (keeps fan on for 20 minutes after no longer sensing motion), but a 0-60 min. spring wound timer switch, with hold feature, is my second choice.


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