Secondary glazing and condensation, are relative in that the glazing is done to reduce condensation on the windows. It will never eliminate it completely but does reduce it if the glazing is done correctly. Secondary glazing is placing a sheet of glass or plastic over the window to help reduce noise and condensation. It is less expensive than replacing the whole window.
The problem with this is that it will not completely get rid of the condensation and that can cause the window to rot from the inside out. The most common is the steam that covers the windows. This happens mostly in winter when the internal temperatures are higher then the external are low.
If this condensation does not dry out in a timely matter, it can cause some damage. The wood swells due to the moisture and molds will grow along with a musty smell. Sometimes the condensation will run down in to the walls, and cause damage that you will not know of immediately. Better to eliminate it before the damage starts.
When the condensation is not taken care of on windows, it can cause some serious damage. In older homes they had tracks at the bottom of windows with little holes that let the water run out to the exterior. Companies use the secondary glazing to reduce some of the condensation. This may result in the wood rot.
It your are not sure how much condensation is too much, if you notice the follow, you need to do something about it soon. The windows stay fogged all day, there is a musky smell, the condensation is dripping down the windows, mildew is growing, and discoloration has started on the walls. You may not see anything but you do notice the smell, means there is some hidden damage.
There are some things that a person can do to help the condensation to cause problems in your home. Ventilation in the bathroom to outside, not inside, drying cloths out side on lines instead in cloths dryer, hanging wet cloths out of living area as a porch. Increasing the changing air in the premises help and changing fuel to electric, as gas has moisture.
Secondary glazing and condensation reduction may not be the answer to the problems. If it is not done correctly, if could cause wood rot in the window frames. And if it does help, it will not eliminate the problem entirely, it will reduce it. Doing preventive work is the smart way to reduce or eliminate condensation all together.