Fix humidity, frost first, then take care of mould
QUESTION: In June 2008, my boyfriend and I bought our first home. We did not get a home inspection due to the pressure of the housing market and information that, if we did, we could lose out on the house. The house was built in 1977 and has an electric forced-air furnace original to the house.
Everything was going great for the first four months. Then I noticed on the ceiling corners of the master bedroom, adjacent to the exterior wall, it was a little darker. I got on a ladder and took a better look. It was fuzzy mould. I cleaned the mould and as I was doing so you could tell that there was a large area on the ceiling that had been re-stippled. My mother stated the mould could be due to high humidity levels, yet our humidity levels were between 38 and 50 per cent. Then more mould appeared about a foot away from one corner. We called the previous owners to see if they had this problem and they said no.
My father went up into the attic to see if he could find the reasoning and discovered that we had Zonolite insulation. Later, we had it tested for confirmation and we found out that the previous owners knew about it. My father moved away some insulation in one corner to look at the vapour barrier and couldn’t find anything wrong, except some moisture between the ceiling and vapour barrier. He unblocked a few of the soffit vents to allow more air flow.
We also discovered that the new bathroom exhaust fan the previous owners installed was not insulated correctly, causing all the exhausted air to expel into the attic space. We’ve corrected that problem, already.
After the first cleaning of the two ceiling corners the mould did not come back, but in the other area came back over and over. I even removed the damp stipple, hoping that would dry out the area and figured that this problem had been occurring for years. The area is cold to the touch and if you move a few inches away the ceiling isn’t cold. One day I noticed frost on the ceiling in that area, which would disappear and reappear later. I also noticed the pantry ceiling corner has condensation.
I’m in desperate need for an answer to what is causing this problem and concerned about repairing it due to the fact that I have Zonolite insulation in the attic. Do you have any answers to the problem?
Thanks, Rachael Hanischuk
ANSWER: To offer answers to your problem we will have to look at both of your issues — the mouldy ceiling and the difficulty with entering and doing work in an attic insulated with Zonolite. Both are intertwined due to the location of the moisture and mould issues.
The first thing that must be discussed is the root cause of the ceiling issue. You have correctly made the assumption that excessive moisture is the culprit for the mouldy ceiling. The difficult thing to determine is whether the moisture is coming from the living space or from an outside source. In many cases, the answer is not clear-cut and the moisture is from both areas.
You may have corrected the majority of the problem by fixing the bathroomfan ducting and opening up the soffit vents. That will take care of the excessive moisture issues in the attic, but may not prevent reoccurrence of the mould.
Electrically heated homes often have a tendency to be damper than those with older gas furnaces, due to the lack of a chimney, which is an excellent method or removing large quantities of moist air from the home. Without a chimney, bathroom and kitchen exhaust fans become more important and may be needed more frequently and for longer periods of time.
A mechanical ventilation system, such as a Heat Recovery Ventilator (HRV), may be installed to further eliminate excessive moisture in the home. Once you have a handle on reducing the relative humidity inside the home and attic, you can deal with the mouldy drywall issues.
If you had typical insulation in your attic, removal of the damaged drywall and replacement would not be that difficult. But if you have confirmed by laboratory tests that the vermiculite insulation contains asbestos, repairs may be considerably more difficult. Cutting out and removing the mouldy drywall may be the only way to prevent reoccurrence. Once the mould spores are embedded in the gypsum or paper of the drywall they may remain dormant until the material becomes sufficiently damp and then begin to grow again. This is why you are seeing repeated mould growth even after you have cleaned the surface.
The only other option is to clean the area thoroughly and remove the surface paper and some of the gypsum core of the drywall before adding another layer of drywall over top. This will only be an option if the mould has not completely penetrated the entire thickness of the ceiling sheathing or if the drywall is not too soft to cover up. If the mould is only on the surface, the paper layer may be removed, along with all the stipple, and the entire surface covered with another layer of drywall.
To prevent new mould growth due to condensation, you may also be able to install additional insulation over the problem areas near the exterior wall that will be resistant to moisture and air leakage. If you don’t have to remove the old drywall completely, you may be able to pull away the vermiculite from the area and install rigid foam insulation or fill any gaps with blown-in foam to seal the area. The difficulty might be to find contractors willing to work in an attic with this potentially hazardous material.
Whatever you do, taking precautions for breathing protection, including proper isolation and cleanup of the area, is critical to prevent inhaling hazardous asbestos fibres present in some types of vermiculite.