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frost on walls – new construction

chuckanduck | Posted in Energy, Heating & Insulation on December 7, 2013 12:28pm

Hi folks.  I am new to this forum and probably am bringing up an old topic so forgive the redundancy…I am looking for advice on a problem with a newly constructed home.  We experiencing our first really cold weather this year and just found frost on an exterior North facing wall – in a stairwell landing between 1st and 2nd floors.  Its in the corner of the wall.  We also have condensation in the corners of some North facing windows.  The house is a custom build with blown in insulation and Anderson 400 windows.  We have geothermal with a heat pump and zone heating with all the bells and whistles, including a humidistat which measures the interior humidity at 30%.  We have a humdifier on the furnace because we have a lot of woodwork and were told to keep the humidity at about 25% in Winter.  However, now that the temps are getting low, (its currently 1 degree above zero outside) in addition to the frost we are finding that there are outlets that have cold air blowing out of them, and as you run your hand along the exterior walls, you can find certain areas that are very cold to the touch compared to most of the wall surface, which is room temperature. I am not an expert on these matters but from what research I have seen, everyone indicates frost/condensation is caused by high interior humidity, but I dont think 30 percent is high enough to be the problem, rather I think its poor insulation.  The house is still under warranty – we’ve been in it for about 4 months.  I will address these items with the builder but would like to be armed with impartial information on this before i speak with him – not that i dont trust him – my wife and I wouldnt have chosen him to build our dream house if we didnt, but i want to be well informed regardless.  :  )    Any information/advice from you folks that know a lot more about this than me would be greatly appreciated!  Many thanks.

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  1. calvin | Dec 07, 2013 07:11am | #1

    chuckandorduck

    Your concerns are warranted for the frost on the walls-windows, you will find can easily show some condensation usually along the bottom half inch or so of the glass.  Lack of air movement across the glass from blinds, drapes, furniture or in the case of radiant heat (no furnace blower), are usually the cause.  R-values of even triple pane glass and their hard smooth surface are still way lower than insulated walls.

    So too would concentrations of more humidity being generated in certain areas-bathrooms, kitchens or areas with plants, aquariums etc.

    The walls are a different story.  Could be a case of no insulation at all in an area or even a moisture source within or near the wall.

    Measuring the humidity in a house or even relying on setting a humidifier seems to me to be not real accurate.  25% and your furniture might start cracking at joints-static electricity from running around on carpet and sparking the dogs nose............35% here is the most comfortable for us.  Cold-sub teens will still show condensation on our glass-but not so in rooms with air circulation (ceiling fans).  We have radiant heat.

    The only real way to "see" a lack of insulation without removing wall finishes would be to use a thermal imaging camera.  You can search and find info-but here's a site that might be worth a look

    http://www.flir.com/thermography/simulator/?pi_ad_id=29221320745&gclid=CKrmoaKJnrsCFa4-MgodCgkAhA

    Fluke makes several.  You might be able to rent, as they aren't cheap.  Or hire an energy audit which will also offer you the opportunity for a blower door test which might uncover sources of air entry (or exit) you don't know exist.

    Here, there was offers from the Gas company to do an energy audit for as low as 25 dollars...........since expired.

    What is the construction of your house?  Framed or slab floors?  Since it's new-there's more moisture being given off by the materials (drywall/paint etc) in the first several months.  But a concentrated area of a wall is reason to be suspect-(don't let a builder fall solely on the vapors of new construction for this one).

    Best of luck.

  2. DanH | Dec 07, 2013 08:22am | #2
    1. Where do you live?

    2. What kind of siding is on the house, and what do you know about the wall construction, in particular, is there housewrap?

    First understand that a new house will naturally have high humidity -- all the lumber and drywall and concrete and tile mud contains moisture and it takes a year or two for it to fully dissipate.  So the humidity will naturally run high for awhile.  But for frost you need both high humidity and low surface temperature.

    There is a corner in this room (office/bedroom) that will generally collect a little frost at 20 below, and another corner in the front foyer.  But generally you should not get frost in a properly constructed house when the temp's only zero.

    The air blowing out of the outlets is a clue -- if it's more than barely perceptible that indicates that the wall is not properly air-sealed on the outside.  We used to get air blasting out of the outlets (and frost in the problem corners at about 5 below) before we resided (1976 house) and applied Tyvek housewrap.  The difference with the housewrap was night and day.  (Folks will tell you that you don't need housewrap if the sheathing is tight, but they're flat-out wrong.  And the problem of poor air sealing is greatly exacerbated with vinyl or metal siding, as it offers essentially no wind resistance.)

    Unfortunately, I don't know what you can do about it, aside from moving or completely residing.  Though if you're really lucky and the problem is only in a few spots, then maybe you can figure out where the air leaks are and seal them.

  3. VaTom | Dec 07, 2013 08:40am | #3

    More documentation would help, as Calvin suggests.  You can buy an infrared thermometer for about $25 that will do a dandy job of measuring wall and window temps.  That will tell you in seconds precisely where you are losing heat fast enough to cause a problem.  Further, you can buy a portable rh/temp monitor for about $40.  We use one to constantly monitor the rh in our house so that we know to adjust as necessary.  The battery lasts several years.  Your wood would be happier at higher rh, but the primary thing it wants is constancy.  No large changes between winter and summer.

    When you have positively identified where the cold spots are, and if you indeed have a rh problem, go to your builder.  Knowing both temp and rh, consulting a dew point chart or calculator will show exactly where condensation will occur.

    Ventilation is not anything you mentioned, and will make a great deal of difference particularly when it gets cold outside.  Was this part of your house plan? 

    Welcome, your questions are of broad interest.  No need for guessing when you have the proper tools.

    1. kxm1 | Feb 02, 2014 06:02am | #8

      good answers tom...

      ...and practical for average homeowner to use.

      what do you mean by your reference to ventilation helping the situation?

      what sort of ventilation did you have in mind?

  4. User avater
    Perry525 | Dec 11, 2013 06:33am | #4

    Surface temperature of everything.

    Buy an infrared temperature gun from Amazon. They are only a few US$.

    Point at anything pull the trigger and you have an instant display of the surface temperature.

    Do keep in mind that if your builder did not take heat bridges into account, where they are will be colder.

  5. FHB Editor
    JFink | Dec 11, 2013 09:50am | #5

    A couple of things.

    Hi Chuck,

    The responses so far have given good thoughts and summaries, but I had a couple of things I want to mention/reinforce.

    As noted, frost is a problem that stems from both temperature and humidity. Your interior humidity isn't excessive, but that doesn't really matter if the surface of the wall is cold.

    It sounds like you have an issue of air flow and insulation gaps. Others have suggested an IR camera to check for cold spots. I've played with IR cameras many times and I can tell you that they are of limited usefulness without being used in conjunction with a blower door test. Used alone, an IR camera just tells you the surface temperature of whatever you point it at. You can do the same thing with a non-contact thermometer, the IR camera just makes it look pretty. If you really want to know what's going on, you need to run a blower door test, then use the camera to look for telltale streaking patterns in the temperature read-out. The streaking is what indicates the flow of cold air, and helps trace where it's coming from.

    Heat moves on air. Blocking the air is your first priority (yes housewrap helps), then insulation. Insulation without airsealing is just an expensive way to filter the air as it flows through your walls.

    1. kxm1 | Feb 02, 2014 06:12am | #9

      great post justin!

      are you an energy auditor?

      at least you recognize the importance of air sealing-most posters on this forum do not seem to get that.

      i agree with your comment about insulating without air sealing being an expensive air filtering system-when fiberglass batts or roll insulation is used.

      however, properly installed (i.e. at the correct density) blown cellulose does a very good job of providing air sealing and a better insulation performance in a retro application where air sealing with other methods is not a viable option.

  6. User avater
    Perry525 | Dec 13, 2013 07:17am | #6

    Home temperature, condensation, frost.

    It is likely that the insulation was wet, when it was

    installed.

    Writing about humidity "30%" doesn't mean anything! To

    make sense of humidity, one needs to know the air

    temperature at that moment. Relative humidity rises and

    falls with temperature. For a given room, as you raise

    the temperature the relative humidity goes down. As you

    lower the temperature the relative humidity goes up.

    If you have a temperature of 90C and a 90% relative

    humidity, then the air is very wet indeed and dew point

    is 87C.

    If you have a temperature of 5C and a 90% relative

    humidity the air is almost dry.

    Once you reach 0C and below, regardless of what the

    humidistat indicates the air is dry.

    Do you have a ground to water heat pump with zoned UFH?

    The thing with temperature and humidity is that fine

    furniture likes things to be steady, as indeed does the

    other wood work in any home.

    I am happy to keep my indoor temperature at between 22C

    and 22.9C, my relative humidity ranges from 45% in

    spring to 70% (it is 70% and 22.8C at this moment)

    Our body temperature is 98.4F/37C (at this moment the

    palm of my left hand is 35C/94F) the wall beside me is

    23C/73F. It feels cold to the touch, after all there is

    a 12C/21F difference.

    Have you bought the infra-red temperature gauge?

    I am not too sure what you mean, when you write; certain

    areas are very cold, compared to most which is at room

    temperature?

    The frost on your wall is entirely due to the outside

    temperature being below 0C/32F, the frost indicates

    that, either your indoor temperature is below freezing,

    or it is not high enough to melt the frost. 30% indoor

    humidity is very low and can/will cause discomfort.

    When you get the infra-red temperature gun, go round the

    house, check the temperature in the centre of the

    windows and doors, and the walls above, below and on

    either side. Check carefully, get up close to the

    corners and the area where the ceiling meets the wall.

    Do the same on the inside. This will show where there is

    missing insulation. Check during the evening or early

    morning before the sun comes up and distorts the

    readings.

    1. DanH | Dec 13, 2013 06:17pm | #7

      30% indoor humidity is very low and can/will cause discomfort.

      I can assure you that 30% humidity (at roughly 68F) is quite appropriate for outdoor temperatures below 5F or so.  And drop that about 5% for each 10F below that outdoor temp.

      It does depend to a degree on the construction of the house, but you need to roughly observe that schedule just to avoid excessive window condensation on standard insulated glass windows.

      1. kxm1 | Feb 02, 2014 06:40am | #11

        wrong...again...dan!

        Please visit the wikipedia site and read the excellent definition and explanation of relative humidity.

        you do not understand what that term means and should not be posting inaccurate-or just plain dead wrong- information on this forum.

        a relative humidity value can exist at any air temperature at anywhere between 0% and 100%.

        you should understand at least some basic thermodynamic principles before you start trying to be a know-it-all and advise people about those principles. people asking for help understanding these issues do not need to nor should they be misled.

        1. DanH | Feb 02, 2014 08:43am | #13

          a relative humidity value can exist at any air temperature at anywhere between 0% and 100%.

          That I agree on.  But if you have air at 50% and cool it, RH will go up.  If you heat it, RH will go down.

          You're the one posting inaccurate information.

    2. kxm1 | Feb 02, 2014 06:28am | #10

      you missed it perry...

      ..again!

      relative humidity does not rise and fall with air temperature.

      relative in the term relative humidity refers to the air temperature/water vapor concentration relationship.

      since colder air can not contain as much water vapor as warmer air can, the concentration of water vapor is lower in  colder air.

      water vapor concentration is technically (or, thermodynamically speaking) referred to as water vapor pressure.

      see te excellent definition of relative humidity at wikipedia.

      water vapor pressure saturation point is lower in colder air than in warmer air but at any air temperature the relative humidity can-theoretically at least-be anywhere from 0-100%.

      1. DanH | Feb 02, 2014 08:40am | #12

        relative humidity does not rise and fall with air temperature.

        That is pure BS.  Look at a dewpoint chart some time.  "Relative humidity" is "percent of saturation", and saturation occurs when the temperature and the dewpoint are equal.  Take an enclosed volume of air and heat it -- RH will go down.  Cool that air and RH will go up.  Dewpoint is the proper way to measure the "absolute" amount of moisture in air.

        Honestly, you call yourself an expert but you haven't got a clue!

        1. kxm1 | Feb 02, 2014 08:52am | #14

          here we go again!

          you are just plain ignorant dan-and often obnoxious!

          first-you referred to me as an expert so i guess my accurate information contained in my posts is some kind of threat or at least an irritant to you.

          i do not post information on topics i am not well informed about.

          as i have already stated in prior posts-relative means relative.

          RH is expressed as a percentage...please do your homework and study the thermodynamic principle involved here.

          then get back to us and explain what you have learned about this topic.

          I did not discover or fabricate the princples of thermodynamics involved in the explanation of RH.

          remember this fact dan as you try to comprehend what i am discussing here: air temps of 30 below and 100 above will both have an RH expressed as a percentage (...a percentage of what dan?..) and that percentage can be anywhere between 0 and 100-that is how percentages work!

          please get with the program dan...please be gone from this forum!

          1. DanH | Feb 02, 2014 09:17am | #15

            Strike two!

            Yes, RH is expressed as a percentage.  Pretty much everything else you've said about it is wrong, though.

            And, like I said, I'm quite familiar with thermodynamics.  It was a required course in engineering school.  (Though the link between thermodynamics and this "discussion" on relative humidity is tenuous at best.)

          2. kxm1 | Feb 02, 2014 09:29am | #16

            thermodynamics..

            ..is totally relevant to this entire forum dan.

            can't believe you have any engineering experience...since you just can not seem to understand what RH is.

            you continue to be 100% in the wrong about this issue.

            i have asked you repeatedly to do the research but you refuse to do it.

            your credibility as a poster on this site in an advisory capacity remains severly jeopardized-and will stay that way until you post an accurate description of RH.....

            keep studying-you have got to get it sooner or later...particularly if you have had any training in thermodynamics as you say you have...which i rather doubt based upon your ridiculous posts on that topic!

            good luck dan!

            i wish you well in your struggle to comprehend RH!

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