Renovation & Design

Damaged ducting likely culprit in dusty house

Replacing corrugated plastic with rigid tubing best fix for multiple reasons


Inadvertent damage to attic ducting can lead to the heating and ventilation system sucking in glass-fibre insulation and spreading it throughout the house.

Question: I read a previous Ask the Inspector article in the Winnipeg Free Press, written in March 2013, to a person asking about a dusty house. I live in south Louisiana and have a complicated tale about my dusty house.

It is a wood-frame elevated house on pilings with central air. It’s five years old and has wood siding. The attic has glass-fibre insulation, and two gable vents for air movement. My house has always been dusty and I had a blower test done on it and the company fixed leaks — such as from electrical outlets — and put a zipper bag on the attic entrance and sealed other things, also up there.

After the sealing repairs, the blower test showed big air leakage coming from the floor below the baseboards and from under the kitchen cabinets. So, I caulked the whole house where the mouldings meet the floor, even in the closets. Now, when the central air is on, fibreglass particles are blown into my living space from the air-conditioning vents in the ceiling and has made my home unlivable.

I have been isolated in my bedroom for three months and am at a loss as to what is causing this fibreglass-insulation contamination to occur.

I am guessing that it has to be coming from the attic and not the walls, since I caulked the floor moulding to the floor tile. Do you have any insight as to the source of the fibreglass? I am having a contractor come in two weeks to remove the attic insulation and replace it with denim insulation, which is more hypoallergenic. A company is coming in and cleaning the house after the new installation. This cleaning company is also installing new air-conditioning ducts in the attic, as I suspect the existing flex duct is damaged.

I postulate that the original dust problem was wall-driven and since I sealed the house, the increased negative pressure in the house from the air-conditioning intake causes insulation to be sucked in from the attic.

Could it be a bad construction problem to have such leaky walls? Sorry for the long story, but you seem like you’re knowledgeable about building envelopes and I wanted to email you to ask. I appreciate your input. Thanks.

Joe Vidrine


Answer: When remedial work is done to a home — in your case, air-sealing of the exterior walls and attic — damage can inadvertently be done to other areas or systems. It is likely there is damage to the air-conditioning system, particularly the flexible attic ducts, and this should be investigated and repaired. Depending on the extent of the damage, the ducts may be repairable or should be replaced with more rigid ducting to prevent a reoccurrence.

Air-sealing the attic and exterior walls of your home is an admirable task, but should not necessarily have been done in an attempt to reduce dust. Unless there is extremely poor workmanship, it is unlikely that the excessive dust was coming from outside the living space. It is more likely it is coming in when you open doors and windows and may be a factor of your location or environmental conditions, or from within the living space itself. Since you have now done a fairly good job of sealing the building enclosure, you can look forward to lower electrical bills, attributable to less cool, air-conditioned air leaking out of the living space.

I think you are correct that, unfortunately, it appears some damage may have been done to the flexible ducting for the air conditioning during the attic repairs. In our climate, it would be very difficult to put ducting for the cooling system in the attic, due to the high probability of condensation and frost on the ducts in the winter. There are a few homes that have this type of system installed, often with small ducts under high pressure when the system is operating. These have to be very well sealed and covered with extra-thick insulation to prevent problems.

In your climate, where the attic is typically warmer than the living space all year round, condensation would not be as big a concern. So, installing flexible plastic ducting may be a reasonable approach. Unfortunately, there are two main problems with this type of ducting. The first is that the corrugations in the plastic piping can cause considerable constriction to the airflow. This will make the air handler and condenser work harder to push the cooled air through the ducting. This will lower the efficiency of the system, raising the electricity consumption. The other concern — particularly relevant in your case — is that the plastic ducting and connections are easily damaged.

Because the plastic is thin, and the pipes are connected to ceiling registers or other connectors with tape or clamps, they have a tendency to come loose or get punctured after installation. A few small holes in the ducting may be easily fixed with plastic tape, but if a connection comes loose, a large amount of debris could be sucked into the ducts or the registers. This is the most reasonable explanation for the glass-fibre insulation in your attic blowing around your living space. The solution is to hire an HVAC contractor to fix the damaged ducts, or replace them with more durable, solid metal ducting, which rarely becomes damaged enough to have large gaps. It appears you have already contracted a company to do this, but the new ducting should be properly installed by a licensed HVAC technician to avoid a recurring problem.

It appears to me the only way a significant amount of debris from the glass-fibre insulation in the attic could blow around your living space is if there was damage to the ducting in the attic. A disconnected duct or numerous punctures could certainly have occurred during the air-sealing job, and may have gone unnoticed by the contractors if the ducts were hidden by the insulation. Having an experienced air-conditioning technician go in your attic, locate the damaged ducts and repair or replace them with more rigid piping should solve your indoor-air-quality problem.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba ( Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at



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