I was hoping one of you could help me out with this.  I built my house very tight (ICF foundation, SIP walls, closed cell spray foam rim/etc)  This is the first winter we've lived in it, and the window condensation is driving me nuts.  It's -6 now, inside temp is 70, my humidity is 33% (I've got all wood floors so don't want to drop it below that.)  I've had to run a dehumidifier to get this low indoor humidity.  I can run my HRV on high, but then the air temp at my floor registers is really cold and the boiler has to kick on to compensate.

If I had forced air I don't think I'd have this problem. 

Right now I run the HRV 20 min on and 40 min off, this maintains humidity at 32-33%, but the condensation persists.  What's even worse is the ice now forming at the bottom of my windows!  (These are not cheap windows,  Andersen 400 series casements, with wood interiors that aren't going to like all that water/ice)

It seems counterproductive to spend all the extra money on insulation to cut my heat expense, but then have to run fans/dehumidifiers/HRV on constant, just to take care of the humidity.

Maybe you can build a house too tight.  I've always read and been told you just make it breath mechanically with an HRV/ERV and you're better off.  But my neighbor with his fiberglass insulated house and forced air doesn't have condensation issues or high monthly heat bills.

Did I get suckered with hyped SIP/ICF/radiant advertising?

Ben

Go to Energywisestructures.com. They deal with this problem all the time.

Your problem is not related to the type of heat but as you implied the type of contruction you employed (well done by the way).

We learned this lesson over 20 years ago. You will save money by using your heat recovery ventilator full time if necessary. There is much information about humidity and condensation available. My RH in the house today at -12°F is 20 and no condensation on the window.

A properly sized (designed) HRV or ERV will easily dehumidify any residence regardless of construction type.

Read your manual and have a Merry Christmas.

I agree the problem is not related to the type of heat, but the type of construction. In my professional opinion airtight housing relying on mechanical ventilation is totally unwise. Humidity problems, mold problems, and fresh air problems are associated with airtight construction such as SIPS. I was heavily involved in designing and building a passive solar home displayed on the National Mall in Wasington D.C. in October 2005 and grew disenchanted with that construction method. Living in a styrofoam/ OSB house is not my idea of a healthy life. Breathable wall systems are ideal in my opinion. Breathable, not leaky. Light Straw-Clay, strawbale, and Durisol block are three breathable exterior wall systems I prefer. If interested check out www.econest.com to learn more about straw-clay breathable walls.

Intriguing.

When working in New Mexico I too experienced these construction methods; though mold, humidity and fresh air were not a concern in the high desert.

Still, some research was done 15 years ago or so (forgive my bad memory) concerning the poor - but still enforced - practice of applying a vapor barrier to basement walls, thus trapping moisture instead of letting the walls and insulation "breath" as the seasons progress.

Traditional stucco also "breathes", come to think of it. I guess I won't get any sleep next year either.

However, after following the link provided, and doing due diligence (web search),  I found an even more interesting link.

http://www.qi-whiz.com/node/620

Facts are tougher than a bulls ars.

the only arguement I've ever seen against mechanical ventilation is "what happens when the power goes out", which is easily answered with "open a window, they still work..".

"Breathable" walls still require more ventilation than happens through the wall. Those wall systems are apparently excellent as far as mold and humidity issues are concerned, but it doesn't count as a bathroom or kitchen exhaust and it does little to reduce pollutants in the space. I would go so far as to wager than a mechanically vented space with offgassing from OSB is better indoor air quality than a "breathable" home without it, at least the OSB offgassing is being diluted with actual fresh air and exhausted at some point, instead of just building up pollutants from cooking, combustion, aspiration, etc .

I've worked on straw bale houses though... nothing long term, but initially at least it seems to be a fine method and man, it sure allows for some cool looking walls.

I also don't have any problem with people venturing outside the boundaries of established science in their home construction or anything else. Science is a fine baseline, and you venture outside of it at your own risk, but it doesn't know everything either. Note that the new thing in nutrition is realizing that perhaps we were healthier when we ate food that wasn't pumped up with hormones, pesticides, and artificial fertilizers. All stuff science told us was ok..

What about the idea of adding a low temp coil on the HVR off your boiler to assist in drying the air as it is moving, or a Hi-V to move the air and provide cooling in the summer?
Dan

Help me out here Dan, what is a low temp coil, or a Hi-V? 

I've got full ductwork for my A/C, with the air handler in the attic.

Incidentally, the temps were in the mid 20s today and the condensation is gone.  Looks like my HRV can keep up till we dip to the teens and below.

I would be interested in knowing more about the possibility of adding something that dries the air.  Right now it's mainly from cold outside air mixing with humid inside air and causing water to drain in the condensate line from my HRV. 

Thanks your your help.

Ben

Rob, I'm not saying mechanical ventilation is a bad thing. What I am saying is that building a house that DEPENDS on it to maintain good indoor air quality and humidity levels is crazy in my opinion. I'd rather be in a house with a non-toxic breathable skin and good mechanical (or passive) ventilation than an airtight styrofoam and OSB box that depends on mechanical ventilation to bring in fresh air to dilute the off-gassing of those materials and to moderate humidity levels. One of the beautiful intrinsic qualities of clay, either as earth plaster or in earth/ straw matrices such as light straw-clay, adobe, or cob, is that clay is naturally hydrophilic (water loving) and hygroscopic. It will pull moisture out of the air and dehumidify it, then later release it when the air is drier. A sort of fly wheel effect.

Ben,

You might want to look into getting a desiccant wheel dehumidifier to solve your condensation issue. A fellow competitor from the 2005 Solar Decathlon in Washington D.C. installed a desiccant wheel in his team's house (Cornell University) to dehumidify the incoming fresh air. It worked great. There's was the only house on the Mall that met the required humidity levels during the competition.

I will always love passive methods, but I see nothing crazy about requiring mechanical ventilation either. Offgassing stops after a relatively short period of time, after all. Don't get me wrong; I don't LIKE offgassing, and I do like passive/natural building methods for sure. But I'm not yet so sure that everyone in america should be building strawbale as well.

Ben we also have Anderson’s, but with double hung and storms on every window. Everyone told us storms weren’t necessary because we had good windows, but we don't have any condensation issues at -5F with 35% inside. I hate to tell you but unless you add storms you have to get the humidity down to prevent it, you will have to play with the ratio of indoor humidity to outside temp. In our last house they told us we had to be below 20% at –5F and that’s just the way it is.

The only other thing you could do is get small fans and blow air across the windows, it doesn’t take much air movement to greatly reduce the condensation. Try it on your worst windows first.

Also if you have shades or heavy drapes it will be more likely to condense because it traps the cooler humid air between the drape/shade and the cold glass, sort of the opposite of moving air across the windows.

Oh one more thing, since you house is new even though your "air" humidity might be 30% the structure itself will likely be radiating more humidity since it is new. Next year after it dries out some more it will likely be a bit less of an issue, you could speed this process by dropping the humidity a lot this winter, but with the wood floors you don't want to go to far.

Thanks Brock,

I'm not too thrilled about the storm window idea... but if that's what it takes....

I have wondered about the the new house syndrome and if we'll have similar problems next year.

Have a Merry Christmas.

Ben

The proper ERV will control humidity.

Badger-

I'd actually asked for an ERV instead of an HRV, but my installer said we're too far north to need an ERV.  Is that true? 

I'm at 52240, southeast Iowa.

I ran the HRV on minimum all last night when I saw the forecast for temps in the single digits.  This morning the condensation on the windows was less  (about 1/2 to 3/4 inch at the bottom. 

I've also noticed my hardwood floor is starting to show signs of movement.   I don't think I want to go much drier in here.

Ben

What was your humidity when you had less condensation? Is there condensation on pretty much on every window or are some worse? (thinking fan idea again).

Brock-

The indoor humidity has been 31%-33% for almost 2 weeks now.  The condensation is on all windows whenever the outside temp gets in the low teens.   When it stays in the single digits for more than a  day the condensation forms little ice dams on my north and west windows.

Now that it's 34 degrees you'd never know I have issues with condensation.

I've tried running my ceiling fan and air handler on high just to get air moving around, but it's not directed at the glass so it doesn't really take care of it.  I leave our curtains up about 6" to allow for whatever circulation there might be.

Thanks for your help!

Ben

Ben;

 

what type of windows are in your house?

I've got Andersen casements. 

Ben