Condensation on sliding glass doors interior

[Robert Olive]

My father in law asked me about condensation on the interior of his dual pane sliding glass doors. This is a new contruction (condo) in Myrtle Beach, SC. The condensation is not between the panes but on the interior surface only and is causing moisture to develop at the base where it meets the carpet which is a mold concern. I would appreciate any advice or suggestions based on your experience. I believe it from a high humidity problem and that a dehumidifier might be in order but want to get advice from this board on how to proceed. Any advice would be greatly appreciated. Thank you in Advance.

[Joe Laurieri]

You are correct.

However the problem is usually due to a failed gasket seal on either the exterior or interior door seals around the doors themselves.

Usually replacement and/or repair of the seals does the job.

Cheers

[Mark Aakjar]

What type of heating system is in the home?

[David J. Smith]

The humidity in a newly built home will be higher as the building materials dry out. This condition will correct itself with time. In time being is may be helpful to install a dehumidier. As the exterior tempertaure goes down the interior humidity should be reduced to avoid condensation on widows and doors. Measuring the humidity level of the interior air will give you an idea of what is going on. Using ventilators exhausting to the exterior for stove and shower while cooking or bathing will help keep humidity levels down. Of coarse the clothes dryer should also be vented to the exterior.
There is some useful info on a Canadian Gouvernament web side, you will have to translate C to F.
Condensation and humidity (http://oee.nrcan.gc.ca/residential/personal/windows-doors/condensation.cfm?attr=4)

Humidity and the Indoor Environment (http://www.blueflame.org/datasheets/humidity.html)

[Joe Laurieri]

I believe David is correct.

Especially since it is a new construction.

If the problem does not clear itself uo.

The installation in terms of the tyvk installation may be in question.

If the Tyvek has not been properly wrapped prior to door and window installation

[Robert Hronek]

I would check humidty levels in the home. If the home has a humidifier what is it set at. Other sources of moisture are kitchens and bathrooms.

Humidity comfort range is from 20 to 65%. In the winter with cold surfaces the humidity level should be at the lower end of the range, 25% is good.

Typically cold outdoor air has a low hunidity level.

[Jerry Peck]

Humidity comfort range is from 20 to 65%. In the winter with cold surfaces the humidity level should be at the lower end of the range, 25% is good.

20% to 65%?

The comfort range is 45% to 55%, maybe 60%.

Get below 40% and your skin begins to dry out, down around 35% and you skin really dries out and become real itchy ... an you are saying 20% is okay and 25% is good?

[Vern Heiler]

My father in law asked me about condensation on the interior of his dual pane sliding glass doors. This is a new contruction (condo) in Myrtle Beach, SC. The condensation is not between the panes but on the interior surface only and is causing moisture to develop at the base where it meets the carpet which is a mold concern. I would appreciate any advice or suggestions based on your experience. I believe it from a high humidity problem and that a dehumidifier might be in order but want to get advice from this board on how to proceed. Any advice would be greatly appreciated. Thank you in Advance.

My advice is to get a cheap humidity/temperature meter that records the min and max readings, Radio Shack has them. If the condo is near the ocean there is a lot of moisture in the air and every time a door is opened it comes inside. The meter will tell you if moisture levels are getting above 55%, which is were most are comfortable. If high readings are seen a dehumidifier can help, but open a door with the ocean breeze coming in and you start over. One fix may be to direct conditioned (heated) air at the glass doors. Maybe you can direct a register or use a small fan.

[Robert Hronek]

20% to 65%?

The comfort range is 45% to 55%, maybe 60%.

Get below 40% and your skin begins to dry out, down around 35% and you skin really dries out and become real itchy ... an you are saying 20% is okay and 25% is good?

In the winter I keep my humidifier set at 25% and dont have problems. During really cold spells I turn it down.

The following info is from a BSI publication on relative humidty. The author is an ashrae fellow and a phd.


As can be expected, individual sensitivities and susceptibilities vary greatly, and it is typically very difficult
to generalize with respect to relative humidity and health. Having said it is difficult to generalize, we will
do so anyway. Keeping relative humidity in the 25 percent to 60 percent range tends to minimize most
health issues – although opinions vary greatly.
Incorrect recommendations in the popular press often lead occupants and homeowners to over humidify
homes during the winter. The range of 40 percent to 60 percent relative humidity is commonly incorrectly
recommended for health and comfort reasons. As we will see, there is a big difference between 25

percent as a lower limit rather than 40 percent – particularly in ver

y cold and cold climates.


To complicate things further, most people are not capable of sensing relative humidity fluctuations within

the range of 25 percent to 60 percent. If the relative humidity drops below 25 percent, most people can
sense it. Similarly, if the relative humidity rises above 60 percent most people can sense it. In the range
of 25 percent to 60 percent the majority of people cannot sense any difference. The range of 25 percent
to 60 percent is typically defined as the comfort range for this reason. This is very different than people
sensing temperature variations. Most people can sense a difference in temperature within a range of 1 to
2 degrees. Less—below 0.1 degrees—if they are married (just kidding).



There is a fundamental difference between relative humidity measured in the middle of a conditioned
space, and the relative humidity found at surfaces due to the significant difference in temperature typically
found between surfaces and the air in the middle of a conditioned space.
For a given sample of air containing water, relative humidity goes up as the temperature goes down. If
the air in the middle of a room is 70 degrees at a relative humidity of 40 percent, any surface below 45
degrees will be able to condense water. Any surface below 54 degrees will have air adjacent it at a
relative humidity of 70 percent – the mold limit.
Whereas when air in the middle of the room is 70 degrees at a relative humidity of 25 percent, the
temperature of a condensing surface drops to 32 degrees from 45 degrees. And a surface with a relative
humidity adjacent to it of 70 percent drops to 40 degrees from 54 degrees.
In other words, for condensation to occur with air at 70 degrees and a relative humidity of 25 percent,
surfaces need to be colder than 32 degrees. For mold to grow, surfaces need to be colder than 40
degrees. Of course, in a nice and happy coincidence, mold does not like to grow at surfaces below 40
degrees, but will happily grow at 54 degrees. What does this tell us? Well, if surfaces are likely to be
cold – say like in the winter - you are better off having a lower relative humidity.


When I orginally posted I did not know the climate he was in which he later reported to be coastal. So he has cool but not cold winters. Being a new house I would assume fairly well insulated. Indoor surface temps should not be very low. I would also assume that indoor surface temps are above the dewpoint of outside air. If the thermopane seal is not broken then the glass temp should be relatively warm - above outside temp.

If the outdoor dew point was very high there would be condensation on exterior surfaces but this was not reported. I think this points to a high indoor humidity level. If a humidifier is in use it should be turned down. Bathroom and kitchen fans should be used when bathing and cooking.

Mold growth can occur when relative humidity is aboove 60% and this humdity level may be occuring on exterior walls and windows. We know the humidity level on the window is above 60%.

More has to be done than just keeping the window above the dew point. Interior surface can be warmed or the humidity level dropped so that surface relative humidity is kept below 60%.

[Jerry Peck]

The following info is from a BSI publication on relative humidty. The author is an ashrae fellow and a phd.


That is from "Dr. Joe".

I can tell you from experience that what he says it true "Keeping relative humidity in the 25 percent to 60 percent range tends to minimize most
health issues – although opinions vary greatly." and that when I was inspecting in South Florida that my clients ALWAYS could tell when the relative humidity dropped below 35%-40% as their skin would dry out and start itching - which I would confirm the RH level and, when the a/c systems were adjusted to keep the RH between 40%-50% their problems would go away.

Keep in mind that South Florida is generally considered a pretty humid area, so going from a humid area (outside and in other places) into a "drier" house and spending time in that "drier" (i.e., less humid) house, they would notice the difference and it would create discomfort.

If one lives in a "drier" climate (i.e., a less humid climate) then maybe 25% would work, but not for what I have experienced where I've been.

[Vern Heiler]

Robert, one other thing that may be causing the condensate is possibly one of the simplest. As Joe Laurieri eluded to the cause may be due to the seal at the bottom of the door. Not bad, just not working due to the height of the rollers on the bottom of the door. If the door is set very high the air will leak past the flock seal and cause the bottom of the door to be cold. Just a thought that you may have over looked.

[Robert Hronek]

I think if the door leak were excessive then it would be clearley noticed. The first area most windows show condensation is along a bottom edge. In this case the bottom of the sliding door is near the floor and I would suspect being somewhat colder than a window 3 feet about the floor.

A cold draft of outside air would introduce dryer air then indoor air. The worse the air draft the more dry air flow which would displace the moist indoor air. Although this may cause the bottom of the door to be colder it would be warmer than the dew point of the exterior air leak.

I grew up in a house with single pane windows in the midwest. My brother slept with his window cracked no matter how cold it was. I never remember his window being wet.