mold question

Hello guys

got a question here. ok , i inspected a house and i found mold spots on the window frames (pretty much more than half of them)…none on the walls , or ceiling …only on the window casings (inside corners)

note that the window frames are PVC or plastic coated

the house was dry…so what could be causing this?

appreciate your replies


Patrick, I have the same problem in my own home and I think it is due to the type of " non airflow heating system ". I have hot water in floor heating and also don’t have an air exchanger. Condensation can get excessive under certain conditions on the windows if I leave the blinds closed or even at night when I keep the bedroom door closed (to keep the cats out). If we just keep up on the house cleaning, the mold cleans up easily.

If anybody thinks this is more of another issue please say so cause I would like to know too.

This indicates that too much moisture present in the home.

Recommend lowering the humidity and improving ventilation.

There is many ways to do that, attached is a few.


It will happen in homes with forced air heating and HRV’s!

I see it especially behinds the screens of casement/awning windows left in place for the winter. Manufacturer’s recommend that interior screens be removed for the winter. The screen will allow water vapour to move to the window surface but essentially blocks warm air flow to the window surface to keep it warm enough to prevent/reduce condensation. This gets much worse when drapes/curtains are left closed overnight.

There is usually a bit of a window design flaw involved also. The old style square metal tube spacers have next to no R value (glass-metal-glass at sealed pane edges). Due to natural convection, cooling air currents from top to bottom of the window sashes let the lower edges get colder first…that’s where the condensation first appears.

Even the higher efficiency low “E” and argon/krypton panes have the cold edge effect when a regular spacer is used. To get better performance, you must use a pane with a “warm edge” spacer.

1986 in my then home town: my company did work (ventilation/insulation) on the new $million/s+ house (17 acres on a lake, in-ground pool, each bedroom had own bathroom) for the president of a large regional wooden window manufacturer. We got to talking about windows and energy efficiency features, vinyl windows, etc (at that point, I had been selling vinyl windows since 1983.). I saw the energy features on this house’ windows but he said it was hard to sell the extra features. I said he had to get moving into vinyl or fiberglass windows and push the energy features…

10 years later, I was called by a group of homeowners in Cape Breton, NS (essentially a small class action) with his company’s wood windows failing prematurely. They wanted me to inspect and write a report on their behalf in a lawsuit they were preparing.

Too bad for them as the company was just entering bankruptcy!!


thx Guys…this is logical… great advices!

I keep about a cord of fire wood in the house during the winter but with the dry heat from the stove shouldn’t it burn off that moisture ?

Actually thinking about that, The wood stove is in the basement and the bedroom window that is worst is my bedroom upstairs opposite end of house. Probably due to closing the door at night and keeping it cooler than the rest of the house. The cooler surface with two bodies emanating moisture in the room would make the cool windows or frames condensate.

Is this a correct analogy.

You got it!!

This works.

This works.

Not in my case, I don’t use a furnace.

The other thing to consider is air flow. Moisture on my new windows would cause mould on the frames. By installing some ceiling fans & turning the exhaust vent on in the bathroom my moisture & mould problem disappeared.

I frequently air find tight homes can be helped big time by the installation of a dehumidifier .
Keep the Humidity at 50% or lower and this could be a big improvement .
I have one in my Home ( Electric heating ) and I drain it into Laundry tub ( never have to MT it.) works great when needed .
We also vent Kitchen and Bath rooms on Timers ,and Dryer to the outside .

Had a quick look at the Plusaire website…It’s a lot weak on the house-as-a-system, building science and ventilation needs of the house!! I would definitely not recommend it.

Not many dehumidifiers can bring the RH below 50%. These things are usually bought by people who have basements with high RH (> than 60-65%) in the summer. OPnce the basement gets > 65-70% for extended periods, mould/mildew will begin to bloom although there has been no wet areas from spillage/floods…the fungi spores can start to grow simply by the fact that there ios enough water vapour in the air.

In the winter’s coldest weather (below -15/20* C; +5/-4* F), it may be necessary to bring house RH down to as low as 30-35% (may feel a bit dry for humans) to keep water off windows. A dehumidifier will not do that!

Must be your salt air I know of at least 5 including me who it works great for. Right now my Inside humidity is 51% main floor and basememnt is 36% outside 71% temp inside is 72° F out side is 70°F

Here is some more information for you…