Condensation issues in house
Hi All
I am looking for some advice for a condensation problem I have in my house.
90s construction in Northern California, house located about 10 miles from the coast.
I have lots of condensation on some of the older (original dual pane) windows on the West and North side of the house through the winter months. If I don’t mop it up everyday it pools and has caused some surface mold.
I had originally thought it was just the windows that were old and needed replacing.
Looking at the problem in some more detail
Relative humidity is between 45 and 65+% through the year – I think being close to the coast and having misty mornings is contributing.
I purchased a standalone 50 pint dehumidifier – This is running 24×7 and has 100% stopped the condensation and brought the RH down.
There are close fitting honeycomb shades on all of the windows – This has not helped the condensation issue.
Crawlspace does not have a vapor barrier, lucky house is on the top of a hill so water drains away very well.
Originally I was going to replace 5+ windows but now thinking there is a better plan
-
Windows – Don’t replace now
-
Crawl space – Install vapor barrier
-
Install whole house dehumidifier
I welcome any thoughts on this, I had not had to deal with condensation before.
Thanks
Ben
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Replies
I'd say you need a bigger dehumidifier.
Even efficient windows will see condensation with close fitting cellular coverings, particularly at 45-65% RH. You’ll need to leave gaps top and bottom and make sure the coverings are spaced away from the glazing as well.
If you're not measuring, you're guessing.
Get some recording temperature/humidity sensors, you can get them on Amazon for around $20.
In the original post there's nothing about temperatures, relative humidities without temperatures are essentially meaningless.
In order for condensation to form on a surface, that surface has to be colder than the dew point of the surrounding air. The temperature of the inner surface of a window is going to be somewhere between the outdoor temperature and the room temperature. So if you're getting condensation on the inner surface but not that outer surface, that tells you that the dew point inside the house is higher than outside. So something inside the house is contributing humidity to the inside air. This is also consistent with inside relative humidity as high as 65%, which is quite high for heating season, and with a dehumidifier helping.
It's really more effective to eliminate sources of humidity than to try to remove the moisture with a dehumidifier. I would immediately suspect that there is a flaw in the building envelope somewhere and rain water is leaking in. I'd rule that out because it can cause significant damage over time. The uncovered crawl space is also a suspect, that can be easily remedied with a sheet of plastic.
I have 'some' data, the attached graph is temp and humidity from the end of last year - this is before the dehumidifier and when condensation and mold was an issue.
Building envelope - I am going around trying to find obvious penetrations, I already found a large fist sized hole to the crawl space from where the master bath was remodeled a few years ago, that is now blocked up.
Looks like I need to spend some time under the house and also get a blower door test done.
The outside air has less humidity than the inside air, so penetrations in the building envelope make the inside humidity lower. Not that you shouldn't be fixing them anyway, but it's not going to solve your humidity issue and might actually temporarily make it worse.
I'm guessing these are aluminum frame windows? Condensation on those frames is a hard situation to avoid and not necessarily a big deal. I don't find myself in many houses (I'm not in the industry,) but in coastal British Columbia I would bet that if you walked into a large number of houses built between 1985 and 1995 on a winter morning, you'd find condensation on the window frames in the vast majority of them.
So I'd shift your effort away from thinking about condensation on the windows and towards thinking about how to maintain an optimal humidity. It does sound like your humidity may be a little high but as others have said, you should start by monitoring.
Are you diligent about running your bathroom and kitchen exhaust fans anytime you are showering or cooking and leaving them running for a while after? How is your home heated?
Thanks - further details below
Window construction - Glazing is held in wood 'frames' but the overall frame is aluminum - From what I can tell this is an uninsulated U-Channel.
Home heating - Propane furnace supplying in floor hydronic system
Exhaust Fans - Decent shower fan that I set the timer for 1h after every shower.
Kitchen exhaust fan - I will check this weekend but think I remember the home report saying it vents into the crawl space and not outside,
The data in your chart starts to get interesting if you compare to outside data as well. For example, you can look at a few datapoints and see what humidity you would expect if you introduced zero moisture from activities (showering, breathing, cooking, etc.) and zero moisture from the crawlspace and just brought in outside air and heated it.
That can start to give you an idea of how much moisture is coming from the inside/ground vs how much is just a result of your local climate.
This site is good for historical weather (I chose a random city in Northern California.)
https://www.wunderground.com/history/daily/us/ca/redding/KRDD/date/2023-9-29
https://www.lenntech.com/calculators/humidity/relative-humidity.htm
Have you tried putting the monitor in the crawl space?
I have just ordered a few more sensors :-)
Master Bath - Area where condensation was worst
Main Living area
Upstairs
Outside
Crawlspace
I can turn the dehumidifier off for a few days and see what raw data I get.
OK. I picked a day in November
Outside temperature: : 50
Relative humidity outside: 100%
Inside temperature : 68.5
Relative humidity inside : 61%
This is vs 'Calculated relative humidity inside closed space:' from the link of 31.6%.
If I am reading this correctly - I have a much higher inside humidity than I should have ie there is too much humid outside air coming in?
No.
The outside air has a dew point of 50F. The inside air has a dew point of 55F. The outside air is drier, even though it has a higher relative humidity, that's why they call it "relative." The more outside air that leaks in, the lower your inside humidity is going to be.
A relative humidity of 61% isn't terrible, I'd say 60% is the cutoff where it starts being an issue and you're within the accuracy of the sensor of that.
The issue is something within the house is producing water vapor.
Warm air can hold a lot more moisture so if there is a body of cold air and warm air and they contain the same amount of moisture (grams of moisture per kg of air) then they will have different relative humidity readings. There are experts on this forum that I hope will chime in but here is my interpretation:
On a day when it is 50 outside with 100% relative humidity, if you opened up all your windows and doors for a while so that the inside of your house equalized with the outside (the air inside your house became 50F with 100% relative humidity) and then you closed your windows and doors and heated your house to 68.5F, you would expect the relative humidity in that air to drop to 31.6%. There is still the same amount of moisture (grams of water) but on a relative basis, the reading would be lower. Since your reading is higher, that means that you are introducing moisture into the air. That moisture could be coming from a few sources:
- People, pets, etc. breathing, perspiring, etc. (we exhale moisture)
- Showering, boiling water, etc.
- Moisture coming up through your crawl space
- Bulk moisture getting into your building (e.g. a leak in a roof getting your framing wet) and then evaporating into your building.
The kitchen exhaust venting into the crawl space is a major red flag.
First, it does nothing, the crawl space is part of the conditioned space of the house so all the stuff the fan is supposed to be exhausting isn't actually going outdoors but into the house.
Second, it's indicative of a conceptual problem. A house should be built so that there is a sharp line between conditioned space and the outdoors, every part of the house should be either on one side of the line or the other. It was very common -- very common -- in the past for areas like crawl spaces and attics to be neither one nor the other, kind of "half-conditioned" where half is short for "half-assed."
Venting into the crawl space is an indication that someone who was involved with the construction believing that the crawl space was "sort of" outside the building envelope, and no one else being there to catch and correct him. That's indicative that there might be other problems with how the crawl is configured.
You might be onto something - the crawl space is in the ‘sort of’ space. No vapour barrier and also have a vented opening, so it’s sort of outside.
Is there insulation the floor joists?
You have to decide where the boundary is in the crawl space between inside and outside, and then enforce it. Typically your choices are either the floor of the living space, or the walls of the crawlspace.
The walls is usually a better choice, it's less surface area to insulate and it allows you to use the crawl space as conditioned space. Doing so means that the walls need to be air sealed, vapor sealed and insulated. The floor only needs a vapor barrier in a mild climate.
Crawl spaces tend to be damp, an unconditioned one that is exposed to the house would tend to make the entire house damp.
The floor joists are insulated with paper faced fiberglass insulation. There is no vapor barrier.
This article is a good overview of how to handle a crawlspace:
https://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces
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What is your flooring? Are there any penetrations?
Floor construction.
Joists - base floor, hydronic pipes embedded in light weight 'concrete' then finished floor on top.
Penetrations - I am going to check this weekend but the large one(s) are filled.
All
Thanks for all of the help and advice. I think I have a much better idea whats going on now. It's rained heavily over the last few days and also raining this morning - so I went under the house into the crawl space.
The house has piled foundations with a number of ring beams forming different areas at ground level. There are also 4 covered decks all around the house that are supported by these ring beams. Now when it rains, the rain is blown onto the deck, falls through and collects in the areas formed by the ring beams. Now the water cannot go anywhere as it is contained by the ring beams. So it pools (1- 3 inches) and also seeps through into the main foundation area and has saturated some of the soil under the house. Everything points to this as there is a lot more water close to the decks.
I am very pleased to have a good idea where this problem starts but now need to think about how to fix it. Make the decks water proof, sump pumps etc etc.
Thanks again
That obviously needs to be dealt with. In time the foundation can be undermined if the soil gets saturated. My general preference is to give the water some place to go through grading or drains rather than trying to pump it.
At the same time, did you read the article I linked to in post #22? A raised floor like that has to have a vapor barrier, and it has to be on the cold side of the floor. Usually the best way to do it is with a layer of foam below the joists with the joints between sheets taped.
Agree I would rather stay away from pumping. Currently looking at dry deck systems that install on the underside of the deck, might be the simplest solution as I can capture the water at a greater height vs down at ground level and then trying to ensure flow to get it through the foundation and away from the house.
Yep I have read the article and thinking whats the best way forward.
I do not understand what you mean by “ring beams” please post a photo.
Regardless you need to regrade so that all the rain water flows away from the home.
Installing a heavy-duty vapor barrier on the floor of the crawl space is the first step in every plan and should not cost much.
If you decide to convert from the vented to a conditioned crawl space avoid the spray foam purveyors and get sheet foam on your walls. Making sure the crawlspace is well connected to the living space with several vents. If you feel the crawlspace is to dirty or nasty to connect to the living space, get it cleaned to your satisfaction.
Walta
If I put a vapour barrier down currently I would create a swimming pool :-) as some of the crawl space if open to rainwater due to the covered decks.
Pictures would be great. Water dripping through a deck should not result in water collecting in a crawl space.
I have attached a diagram that should help.
Put simply - Some of the crawlspace formed by the foundation walls is open to rainwater due the foundation being shared between the house and covered decks.
I hope this helps.
That seems pretty wild... I'm having a hard time actually imagining what this looks like in the field.
Yep it’s an odd one. Best way to fix I can see. Pour a concrete slab under the decks with drains that tie into the existing downspouts. Should ensure that no water can sit under the decks
Sounds good. The treat the part of the house that overhangs as an unconditioned crawlspace, and the part that doesn't as a conditioned one.
First thing is to stop the water pooling under the decks. I think this is causing lots of the issues. At the same time separate the conditioned and unconditioned spaces by blocking off the access holes between them. What needs more thought is how to deal with the conditioned spaces and also the 50:50 ones.
How much access is there to the underside? Are there openings in the wall? How high off the ground is the floor?
About 2ft clearance under there. All of the separate crawl spaces have access holes between them.