Condensation in new bedroom extension

Hi All,

Long time reader first time poster. and I am hoping I have found the correct area to post this thread. And I apologise in advanced for the lrngth of my post, but I didn't want to miss any details...

OK so as we have come into Autumn which is the colder season here in Melbourne I have noticed that most mornings the inside of the double glazed windows are covered in condensation and there are also condensation patches on the ceiling only around each of the down lights in the room say a 30cm - 40cm patches where there is no insulation in these areas.

A bit of background which could be a contributing factor is that I have had some drainage sub floor drainage issues which were recently fixed, however the subfloor is still damp to some degree. I also recently installed an inline exhaust sub floor fan (fully ducted) as there are a lack of sub floor brick vents due to the natural slope of the land 2 of the 3 walls of this extension area are retaining and natural soil level sits higher then the sub floor hence not allowing brick vents in these walls and eliminating the traditional cross flow sub flor ventilation achieved with bricks vents on each wall.. The sub floor fan has been doing its thing for the last 2-3 weeks set on a timer for 8 hours a day shifting the stale humid air outside.

However given that I have addressed the sub floor draininage issue and ventilation and the floor is drying out im not sure if this is the cause of my condensation issue inside the bedroom. I have double glazed windows (facing south) and guareenteed most mornings they are crying in condensation. The bedroom/extension area was built approx 8 months ago and this is the first autum/ winter we have been lining in this area, and I need to urgently address this issue before it becomes serious i.e. mold, musty smell and flaky paint on ceiling etc...

I built this extension as an owner builder and the entire extension area is fully insulated as per the energy assessment report.i.e. R3.5 in celiing, R2.0 walls and R1.5 underfloor, I initially thought the issue was because the timber floor was absorbing the moisture and humidity from the damp sub floor however not ruling this out i think the issue could also be because this area of the house is so tightly insulated that it doesn't breath and the moisture created inside the house through normal living, i.e. breathing, showering etc.. cannot escape and remains trapped... we also have ducted heating throughout the entire house and even with the return air on the end of the house it doesn't seem to shift the humid air from the affected area as we still have condensation most mornings. just my thoughts and opinion and I am open to all other opinions on this.

I need to work out why this is happening and how I best go about addressing this issue, a friend suggested leaving a window open but in Melbourne during this time of the year is a big NO and he also suggested ducting the bathroom exhaust fan outside as at the moment it vents to the roof space and perhaps installing a whirly bird on the roof to ventilate the roof space but I'm thinking I need some sort of internal ventilation instead to shift out the stale, humid trapped air...


Please, please, please help, I cannot bear this condensation issue much longer!!

Thanks in advanced.


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