Hi,
Various mags have some new products to use on floor and between wall and insulation to help basement not trap moisture. I suppose by nature, some moisture is there because the basement wall is under ground.
Are these new products hype, or do they provide some serious improvement?
Anyone have experience with these new products or ideas of their own on some of the not seen prep work which must go on before you re-finish the basement?
Thanks.
J
Nothing new there. It is an attempt to keep moisture from coming into the basement AFTER it already has come through the wall or floor.
In some cases it may work, but it is going to trap that moisture on the other side of the barrier and in many cases it will not help at all. It all depends on your problem.
Sorry but most of the time the only fix is to keep the water away from your foundation in the first place and second to provide additional ventilation or dehumidifiers.
The problem may be too much uncontrolled ventilation, esp in an older home with lots of air leaks or a slab with no vapor barrier.
Basement exhaust with a differential humidistat (a Smart Vent?) can use
100X less electrical energy than a dehumidifier, climate permitting. My hunch is that most do. A Key West house with no AC might be one exception.Smart Vent's 12/19/2000 US patent no. 6,161,763 "Module-controlled building drying system and process" at
Oddly enough, this patent measures "absolute humidity" in grams/m^3 vs a humidity ratio in g/g, so it looks like the controller would turn on the fan with outdoor air at 95 F and 17.4 g/m^3 and indoor air at 80 F and 17.5 g/m^3, even though cooling 1 m^3 of the 95 F air would lower its volume to (460+80)/(460+95) = 0.973 m^3 and raise the absolute humidity to 17.4/0.973 = 17.9 g/m^3, so this would add moisture to a house.
As an alternative to "absolute humidity sensors" or calculations, we might mount an RH sensor on each side of a single pane window or a steel plate and insulate the plate indoors, except near the sensor, and turn on the fan when outdoor RH is less than indoor RH.
Nick
True, while less likely in my experience it is certainly possible and should be considered.
This came from a Humidex installer who said they help more with older houses.
Nick
Nick, you scare me.
Move to South Carolina and try your idea here. Then after your house rots down, you can move back up north.
It does not matter what the RH differaece is unless the temperature is the same when you ventilate. If the humidity ratio(in grains of water per pound of dry air) is higher outside than it is inside, you DO NOT want to ventillate! If the humidity ratio is lower outside than inside, then ventilating MAY do the trick. Either way, you MUST be sure that the surface temperatures in the basement are ABOVE the dew point of the air present. If the air outside is dryer than the air inside, but the wall temperatures in the basement is still below the outside air dew point, ventillation WILL NOT HELP!!!!!!!!!
A dehumidifier will use more electricity, but is not likely to damage anything. Using fans with an improper control system can rot the walls out!!! The cost of repairing the walls will be MUCH HIGHER than the cost of the electricity saved!
In order to determine the proper fix for the OP problem, I would want to check the weathe data for his area, measure the wall temperatures over time with data loggers and measure the humidity inside and outside over time with data loggers. He will be safe, if a littel poorer with a dehumidifier, assuming he drains it outside or into a proper drain. Using your RH sensor scheme may destroy his house!!!
I can't see how you can recommend such an option without measuring the conditions inside and outside his house with data loggers and his wood moisture in the basement walls using a wood moisture meter.
You have lots of nifty formulas Nick, but seem to have no idea on proper practical application. Here in the "land of the midnight fungus", recommending ventillation to solve such a problem is downright irresponsible!
Please remember Nick, most people with mosture problems do not live in dry climates! Therefore dehumidifiers are usually a better solution to high humidity than exhaust fans.
By the way, if he installs a $250.00 dehumidifier instead of a $1,000.00 Humidex exhaust fan, the money he saves on equipment will be enough to pay for dehumidifier electricity for many, many years!! And his walls will be safe!
Please start recommending practical solutions that are climate specific, instead of your pie in the sky (unless it is cherry pie) control schemes requiring computers and more psychrometric knowledge than the homeowner is likely to ever possess.
Stretch
No thanks. Altho houses in western NC seem cheap. BTW, this scheme might work in a reasonably airtight house that can store some dryth in Charleston, with w = 0.0166 on an average July day and w < 0.0100 from October through April. I could determine that with a little TMY2 simulation. You probably couldn't.
I'm not sure what you are saying or why you are saying it, but it seems to me that you are wrong. For instance, if a basement is 50 F at 70% RH and outdoor air is 40 F at 50%, it's time to ventilate. Perhaps you would like to clarify your claim. I also suggested a way to make a bit of indoor and outdoor the same temp so we could simply compare RHs as a measure of the humidity ratios. Sounds like you didn't understand that. You may be over your head and mired in old cut-and-dried HVAC techniques in this case.
That's what I said (with one L :-)
It will. The question is how often that happens and for how long, compared to how fast the house collects moisture and how much it can store. Looks like it works fine in Phila, with a max 75 wet hours in a row in a typical year.
Now think hard: if we ventilate when the weight of water in a pound of basement air is more than the weight of water in a pound of outdoor air, we are removing water from the basement. If you think we are adding water, where do you think it comes from?
I disagree (with one L and an "are" vs "is" :-)
I suggest using fans with a proper control system.
That might see you into retirement.
Nope. The patent described a technique for drying out flood-damaged houses.
I know... Pity.
Recommending dehumidifiers to solve such a problem is downright irresponsible!
I disagree (about moIsture :-)
Unlike you, I've been doing so all along, with detailed weather data.
Nick
Hi,
Thanks for all the feedback. I don't think I have a problem, but I am wondering if there is low tech method to check the temp of the inside versus the outside. I am thinking just a few data points over the week with a thermometer outside and one inside? Does it need to be on the wall?
I think I am looking for general best-practices if one is in the planning stages for re-finishing the basement. Unfortunately, the basement only has one door to outside, but no windows.
As for best practice, using a de-humidifer appears to be a good one for the list. I have a sump-pump and that could be used to get water out. True? That is where a/c for house dumps it water.
I had seen in a mag some type of flooring material to put over concrete floor and then just thought maybe there were other best-practice construction ideas.
But, it sounds like some solutions might not be good, but depend on the problem. Not clear I have a problem, though.
Any other comments welcome. Thanks for your time and advice.
Thanks.
JIm
Hi again,
Forgot to mention we are on East Coast in Maryland. It does get humid in summer. Winter not too cold, but humidity is always up there during the peak of summer.
Thanks.
JIm
A Smart Vent seems like a much better solution to me.
Nick, The weather data is nice, but only available for selected cities. The weather data says 78 degrees wet bulb here in Myrtle Beach, but I commonly MEASURE over 80 degrees wet bulb.. Yesterday it was 83 degrees wet bulb in Murrells Inlet for 3 hours. Murrells Inlet is just 15 miles south of Myrtle Beach, SC.
BTW, I am glad you are a good speller.
I disagree (with one L and an "are" vs "is" :-)
You can disagree all you want, the walls will still sweat!
Stretch
A time to stop basement ventilation, but unimportant in the long run.
Nick
Nick,
Based on long term data logger use here, the times when ventilation will work is from the middle of Otober to the middle of March. Basically late fall, all winter and early spring. During that time, you may need to worry about freezing pipes.
The further south you go, especially in coastal areas, the more extreme conditions are.
Stretch
We've been through this before. NREL says Wilmington NC has a 63.4 F deep ground temp, with these long-term averages...
Apr May Jun Jul Aug Sep Oct
Avg daily max 74.0 80.8 85.4 88.5 87.6 85.2 76.9 F humidity ratio 0.0080 0.0114 0.0147 0.0168 0.0167 0.0142 0.0099 vapor pressure 0.380 0.539 0.691 0.787 0.782 0.668 0.469 "Hg dew point 56.7 60.6 67.7 71.5 71.3 66.7 56.7 F
No. During that time, we'd move air near the basement floor upstairs vs outdoors to store dryness in the basement.
Nick
Nick,
My MEASURED data does not agree with your book data. Myrtle Beach is only about 50 miles south of Wilmington, NC; so the data should be close. Who is NREL anyway? Spell out and don't use abbreviations so much.
Here in the summer the normal dew point is 75 to 82 degrees. If you used real data nstead of old book data, you would get different results. Any one trying to dry out a basement or crawl space should MEASURE their local conditions any way.
Stretch
Too bad. Perhaps you should measure and average for 30 years, like NREL.
Google is your friend.
I disagree. Short term measurements can mislead, and nearby long-term averages are sufficient, and less trouble.
Nick
Nick, Here s data logger data from one day in June 2000.
Stretch
Date Time Temp DP RH (%)
06/17/00 00:22:17.0 78.88 74.58 87.2 06/17/00 01:22:17.0 78.53 74.72 87.6 06/17/00 02:22:17.0 77.7 74.46 88.9 06/17/00 03:22:17.0 77.27 73.78 88.9 06/17/00 04:22:17.0 77.09 73.34 87.6 06/17/00 05:22:17.0 76.83 73.1 88.9 06/17/00 06:22:17.0 76.48 73.22 89.3 06/17/00 07:22:17.0 77.83 74.02 87.6 06/17/00 08:22:17.0 77.75 73.9 87.2 06/17/00 09:22:17.0 81.53 75.6 82.3 06/17/00 10:22:17.0 82.28 75.96 81.4 06/17/00 11:22:17.0 84.47 77.34 79.5 06/17/00 12:22:17.0 85.6 76.84 74.7 06/17/00 13:22:17.0 86.73 77.54 74.7 06/17/00 14:22:17.0 87.59 77.42 72.7 06/17/00 15:22:17.0 84.02 75.92 77.6 06/17/00 16:22:17.0 87.27 76.58 70.7 06/17/00 17:22:17.0 93.54 80 65.7 06/17/00 18:22:17.0 85.46 76.72 76.1 06/17/00 19:22:17.0 81.04 74.74 81.8 06/17/00 20:22:17.0 79.46 74.96 86.3 06/17/00 21:22:17.0 78.58 74.86 88 06/17/00 22:22:17.0 78.62 75.3 89.3 06/17/00 23:22:17.0 78.8 75.16 88.9
A single day is unimportant.
Nick
Stretch, All Nick knows is books and numbers..... He knows nothing of real life. Remember the old Far Side cartoon whith the scientists looking at the chalkboard that is filled with figures and calculations on both ends and in the middle has some words "Then a miracle happens" ?? Thats Nick
Noon wrote: Stretch, All Nick knows is books and numbers..... He knows nothing of real life.
Remember the old Far Side cartoon whith the scientists looking at the chalkboard that is filled with figures and calculations on both ends and in the middle has some words "Then a miracle happens" ?? Thats Nick
Noon, guess your right. Arguing with Nick is like mud wrestling with pigs. The pigs love it and you get all dirty :-)
Stretch
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