Air conditioning in humid attic - urgent help needed please

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Old 07-27-14, 01:35 AM
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Air conditioning in humid attic - urgent help needed please

So my uncle lives in my attic after going jobless. The space is fairly big and has a lot of the AC plenum box in the attic. I installed a supply vent (one that provides air) in the attic using the existing AC system (it is perfectly fine for that space without affecting the pressure of the system) and the only issue is - the attic IS TOO humid and hot in the summers.

The 1st floor of my house will get much much cooler but his room (which works off the same central air) will be well over 95 degrees humidity.

What can I do about this folks? I'm thinking ATTIC foil but I heard it just makes it EQUIVALENT to outside temperature at best...which would be 105 degrees and the same level of 65% humidity.

In need of DIRE help from an expert on this.

I did NOT install a return vent in the attic...perhaps this was my failure and a reason as to the humidity in the attic?
 
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Old 07-27-14, 06:23 AM
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For proper exchange of air you need a return. Hopefully your system can handle it the extra load.
 
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Old 07-27-14, 06:53 AM
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Attics aren't insulated, actually they need to breath. The envelop of your house it's insulated.
Your never going to cool that space and the air your blowing up there is going right out the vents.
Move your uncle to a room within the house, or help him find some work so he can get back into his own apartment.
 
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Old 07-27-14, 09:02 AM
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If you add a return air in the attic your duct work will probably grow mold.

If it is possible in your application, making an attic livable would involve a general contractor an an additional heating/cooling unit.

I agree with Tom. You need to get your uncle out of the attic.
 

Last edited by Houston204; 07-27-14 at 10:03 AM.
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Old 07-27-14, 01:52 PM
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How would adding a return vent add mold into the ductwork during summer? That makes no sense if the air is so humid. During winter I doubt it could if I seal the attic...and even then I think its a far reach. My chances of mold in the ductwork is not high. You all are asking me to take him job hunting etc but Im looking for practical advice here. A lot of the advice so far provided makes no sense. I had someone in HVAC already test the space for AC and he said my current system can easily handle it...the only issue was the cost he wanted just to retrofit ductwork.

Like I saidm..regardless of breathing as an attic with ONLY soffit vents and natural crevices...I dont think this attic is "breathing" at all. If it were then it would not be so humid...dare I say more so than outside.

Can someone with more experience please post?

Thank you
 
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Old 07-27-14, 02:50 PM
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Just a spring chicken Here compared to those other two I'am sure. A attic has about the same footprint as the foundation.Alot of hot air. If your system can handle it ,seal and go for it or don't seal at all. Nice that your trying to take care of your uncle and good luck.
 
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Old 07-27-14, 03:17 PM
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I have never done the attic cooling before, but from experience, it is hard to see this will work. First, let's forget about the return duct, since you have soffit vents, the return duct won't help much anyway. The problem I am thinking is how do you control the temperature in the attic. I believe your T-stat is downstair, let's assume the outside temp is 95F, you set the t-stat at 75, when downstair room reaches 75F, the AC will stop, at that time the attic may be somewhere around 80F (since upstair always a few degree higher). In a few minutes, the attic will reach 90F because it is open and not insulated. And the AC won't start for another 15 to 20 minutes because your downstair rooms are all insulated. This is all I can think about now, there may be other issues, you need to discuss all the details with your HVAC guy before you start the refrofit work. Many posters here are HVAC experts, not that they don't want to give you practical advice, it is because this one is not that easy.
 
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Old 07-27-14, 04:18 PM
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Any time that I run into organic growth on an evaporator I search for and repair the return air leak that caused it.
 
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Old 07-27-14, 10:11 PM
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Thank you Guk - I will seal the attic and dehumidify the air inside...then I will try to plug up any ridge roof vents (only 1 in the nearby area)...and I am planning on doing ATTIC FOIL to reflect radiant heat. I will cover the soffits first from the outside completely....then I will install a return VENT.....then I will dehumidify it...and finish it off with attic foil
 
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Old 07-27-14, 10:46 PM
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What type of heating do you have?
If you have a gas furnace with metal vent pipe it requires combustion air which would prevent you from sealing the attic too tightly.
 
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Old 07-28-14, 08:43 AM
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May be easier if you can build a room in the attic with walls and ceiling and insulate the room all around. This way you don't have to worry about the air supply as mentioned for the heating system (or hot water heaters or even bathroom vents).
 
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Old 07-28-14, 09:43 AM
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Dear all

Thank you for your responses. Especially mr. forum moderator sir

"If you have a gas furnace with metal vent pipe it requires combustion air which would prevent you from sealing the attic too tightly."

It is a "combustion furnace" But I can't expect to seal the attic 100%. At most, BETTER than what it currently is - thats what I can ask for.

Currently...the attic is HUMID, and the HOTTEST part of the house. I know that mold does not grow in such summertime climates but that level of moisture and barely any real ventilation is NO doubt going to lead to mold UNLESS I DO SOMETHING.

The builders clearly screwed up and I was not in a position to even KNOW that was the case.

I clearly cant SEAL the soffits COMPLETELY...all I plan on doing is just putting either insulation BOARD over them....I don't want to SPRAY foam the soffits, as removing that can be AWFUL. (Am I right?) Plus...the soffit is vented...so spray foam could show on the outside of the house like some yellow disgusting stuff....

I am essentially very much trying to get this done for my uncle. There are no other rooms, I assure everyone here I have exhausted options.


QUESTION FOR THE EXPERTS: I was thinking of SPRAY foam which is about R20....but then changed my mind for DENIM insulation (R-30).

I do however notice the wall cavities in the attic ALREADY has FIBERGLASS Insulation...not sure if R30...but there is SO SO much humidity in the attic I am seriously doubting that insulation DOES anything...it's just not normal...at all.

Soffit vents can't possibly bring that much heat....the only other issue I can see is...the ROOFING has no "reflective" foil....it could be on the TOP of the house...but a part of me seriously doubts it.

Any expert guesses as to why this supposedly insulated attic is HOT AND HUMID (more so than the house).

I guess it comes down to simple logic: theres too many air leaks...and perhaps no reflective shielding for radiant heat? Humid...hot....a nightmare.

Please help anyone who can.
 
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Old 07-28-14, 09:45 AM
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You say the attic is insulated - the floor or the ceiling?

If I missed this in your already posted information, I apologize.
 
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Old 07-28-14, 10:30 AM
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Originally Posted by Michael Landon
Any expert guesses as to why this supposedly insulated attic is HOT AND HUMID (more so than the house).

I guess it comes down to simple logic: theres too many air leaks...and perhaps no reflective shielding for radiant heat? Humid...hot....a nightmare.
-First - climate - which state are we dealing with ?
-Second - what sort of house - row, twin, single? Style? Cape Cod, 2 story? Masonry or wood? Slab or basement?
-Third - surroundings woods, suburban lawns?
-Fourth - how long? "The attic it too hot in the summer(S)" - how many summers?


If I were you....

First thing, paint the roof white. Yes. Paint (tar) or whitewash (asphalt)

A friend worked with Philadelphia PA Health Dept. a few years ago on a pilot program
for green-building ideas. Retrofitting rowhouses by painting the roofs white was a start.
Painting the roof white dropped the roof temp by 50-80 degrees.
Yes, you read that right. Up to eighty (80) degrees.
Interior temps dropped by about 10-15 degrees.
Temperature in the street dropped by about 5 degrees.

Second, instead of a/c try a whole house fan.
When you pump cold air into a space that is in contact with hot roof,
or in contact with the soffit air that is in contact with the hot roof,
the majority of the cooling is expended in condensing water out.

You'd do better by removing the hot air, rather than trying to cool it.
It's called relative humidity. Long story short, humidity increases eh, roughly exponentially with increased temperature. Double the temperature, it will hold 4x the moisture.
If you have hot dry air, add a little moisture you drop the temperature a lot. That's how midwest swamp coolers work.
The flip side of that if you have hot moist air, it takes A LOT of cooling to drop the temperature a little. Instead, you raise the humidity a lot.
 

Last edited by Hal_S; 07-28-14 at 11:23 AM.
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Old 07-28-14, 11:05 AM
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How about a portable A/C venting through the soffit or am I way off base?
 
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Old 07-28-14, 11:44 AM
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Eh, trying to cool the hot air in the attic instead of venting it is
pushing the car up the hill with the parking on to keep it from rolling back....

OP needs a roof vent, a whole house fan, or a gable window with a fan.

- And a white roof.
 
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Old 07-28-14, 05:13 PM
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-First - climate - which state are we dealing with ?

- Southern California

-Second - what sort of house - row, twin, single? Style? Cape Cod, 2 story? Masonry or wood? Slab or basement? 2 story -

soffit holes on one side (not soffit vents)

-Third - surroundings woods, suburban lawns?

Other houses, an mountain - really hot area and humid outside in summers


-Fourth - how long? "The attic it too hot in the summer(S)" - how many summers?

Starting from End of May to September (5 good months with summers the most humid and hot)
 
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Old 07-28-14, 05:17 PM
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"

You say the attic is insulated - the floor or the ceiling?

If I missed this in your already posted information, I apologize.
"

The attic has fiberglass installation on the wall barriers and attic floor....and it seems the roof has some 1/4 inch metal layer.....underneath (though i doubt its doing anything)

Also can someone tell me how to cover up soffit vents WITHOUT spray foam? They are super hard to reach...so not sure if I can buy a "foam board" either.....x_x I'm struggling.


Seriously struggling trying to cover up these big expanses of soffits with tiny holes...like a grill.

I want to keep the HEAT AND AIR OUT from these soffits....if I simply put clear tape on the outside - can this work?
 
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Old 07-29-14, 06:02 AM
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OK, here's the problem as I see it - with the insulation in the floor of the attic, this space is not insulated and not currently designed to be conditioned space. The long term answer, IMO, if you want this to be conditioned space is to remove the insulation in the floor and insulate the ceiling of the attic. You could do this by creating a hot roof or you could install baffles to maintain an airway for ventilating the roof and the insulating (like with spray foam) under that.
 
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Old 07-29-14, 12:48 PM
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Originally Posted by Michael Landon
Seriously struggling trying to cover up these big expanses of soffits with tiny holes...like a grill.

I want to keep the HEAT AND AIR OUT from these soffits....if I simply put clear tape on the outside - can this work?
No.
You need to let the air flow through the soffits.

The hot air flowing through the soffits is keeping water from condensing inside the roof and causing mold. If you think it's bad with the humidity at 95%, that's nothing compared
to an attic where the air is below dew point - e.g. 100% humidity, where everything is damp and moldy.

Quite simply, you need to partially finish the attic by adding air gaps and insulation along the roof.

I would NOT remove the insulation in the attic floor because, for now, it adds sound insulation.
When your guest is gone, you will have a double insulated house
- insulation in the attic floor, and insulation along the attic roof.

With a large dead air space, I'd look at a roof vent or a whole house fan for ventilation.
Or, perhaps, a gable window or skylight for both light and ventilation.

    It sounds like your first step is to install some roof vent baffles. They will connect the soffit
    to the ridge vent, to allow air to flow and keep the roof from rotting and keep the hot air out of the living space where it's a problem.




    Basically, instead of trying to cool all of the hot air in southern California,
    you'll only have to cool the hot air in that room.

    Then see about adding some insulation.
     

    Last edited by Hal_S; 07-29-14 at 01:35 PM.
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    Old 07-29-14, 01:58 PM
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    You guys are saying that I should keep the soffits sealed but are not realizing they aren't doing anything other than bringing in humidity along with the roof. I rather INSULATE the roof (which has radiant barrier BUT HORRIBLY INSTALLED - sandwiched between the roof and the wood....idiots) and then a return vent in there...

    This would be much better and PREVENT humidity.
     
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    Old 07-29-14, 02:30 PM
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    Originally Posted by Michael Landon
    You guys are saying that I should keep the soffits sealed but
    Eh, not quite. The soffit and ridge vent must be connected to allow ambient air to circulate along
    the underside of the roof to prevent condensation and rot.


    Originally Posted by Michael Landon
    are not realizing they aren't doing anything other than bringing in humidity along with the roof.
    Eh, trying to air condition an uninsulated space is what is bringing in humidity. The soffits and ridge vent are reducing the humidity created by the addition of A/C.

    Originally Posted by Michael Landon
    I rather INSULATE the roof (which has radiant barrier BUT HORRIBLY INSTALLED - sandwiched
    between the roof and the wood....idiots) and then a return vent in there...
    No. If you put insulation directly against the roof, it will rot out the roof.

    SOLUTION

    First - increase the albedo of the roof - (paint it white) That should drop your exterior summer roof temperature by about 50-80 degrees.

    Second, install vent baffles from soffit to ridge vent, to protect and vent the underside of the roof.

    Third, air seal the attic so you are not wasting time trying to air condition the outside air.
    Then rough in at least some insulation.

    Fourth, install some form of attic vent to let the warm air out of the attic, and passively pull cooler air up from the rooms below.
     
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    Old 07-29-14, 08:44 PM
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    Hi Hal,

    Thank you for the reply.

    "Eh, trying to air condition an uninsulated space is what is bringing in humidity. The soffits and ridge vent are reducing the humidity created by the addition of A/C.
    "

    This is not correct. The attic is already humid with no AC present. Also the AC units are spackled/wrapped in a radiant heat foil themselves special to HVAC units for furnace/plenum boxes.

    As for the soffits - I rather air seal them and make the entire attic A/Ced and add a 10x6 return grille for the small area which sees my uncle's main quarters.
     
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    Old 07-30-14, 04:32 AM
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    Originally Posted by Michael Landon
    The attic is already humid with no AC present.
    That's what I'm unclear about.
    There is always some humidity in the air, cooling the warm air increases the humidity.

    Would have to work backwards to figure out exact numbers

    First post said -

    Originally Posted by Michael Landon
    {The attic} will be well over 95 degrees humidity.

    What can I do about this folks? I'm thinking ATTIC foil but I heard it just makes it EQUIVALENT to outside temperature at best...which would be 105 degrees and the same level of 65% humidity.
    If you're at 105 degrees and 65% humidity outside, you have 230 grains (archaic weight measurement) of water in that air.



    When you cool that down to 95 degrees, that same 230 grains of water will represent 95% humidity.
     
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    Old 07-30-14, 02:20 PM
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    Hal

    Thank you again for your continued response.

    So you're saying even if I add a RETURN duct into that small space...it will still be humid?

    Surely there must be a way to make a room out of that humid place...sealing it and adding a return vent?
     
      #26  
    Old 07-31-14, 05:45 AM
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    You need to build an enveloped room within the attic space. Building codes will apply.
    You cannot seal the soffit vents and insulate the roof. This will increase moisture along the roof line which will lead to failure of the roof structure.

    Listen to what these guys are telling you. Your attic space needs to breath, air flow must occur on the roof line. Soffits, ridge vents, gable vents etc. they're all there for a reason.
     
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    Old 07-31-14, 08:09 AM
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    Originally Posted by Michael Landon
    So you're saying even if I add a RETURN duct into that small space...it will still be humid?
    Yes. If you add a return duct, then the entire HOUSE will become hot and humid.

    Think of your house, then think of your car, sitting in a large LA parking lot on a sunny summer day.

    When you get into a hot car, do you
    (A) seal up the car and turn on the AC full blast?
    or
    (B) roll down the windows to let the superheated air out, THEN turn on the AC?

    Separate yourself from the hot roof and hot air BEFORE you try and cool anything.


    Basically, on a 95 degree day, the roof shingles are probably eh, 150 to 180 degrees in full sun?
    The shingles are nailed to the attic, so they conduct heat into the attic.
    The inside of the roof is probably 120 to 150 degrees?
    Go into the attic, put your hand on the south facing part of an uninsulated roof at noon.
    I will be hot - way too hot for any home AC to attempt to cool down a 180 degree roof.


    So, you use convection and baffles to cool the roof.
    If the roof is 150, then having roof vent baffles from soffit to roof vents actually cools the roof by conducting 95 degree outside air along the underside of the even hotter roof.

    Then, you use insulation to separate the roof from the cooled living space.


    Originally Posted by Michael Landon
    Surely there must be a way to make a room out of that humid place...sealing it and adding a return vent?
    1) White roof - drops the roof shingle/tar temp by 50-80 degrees.
    2) Vent baffles - cools the hot roof by directing ambient air along the underside of the roof
    3) attic insulation and sealing - means that you only have to cool the air once, rather then trying to constantly cool new hot air.
    4) attic vent and fans - if your AC is comfortable on the lower floor(s) that cool dry air will pickup some heat and moisture.
    However, even warm dry air will feel cool in the attic if you have a fan circulating it.
    And, with a simple passive roof vent, the warmest moist air will rise and exhaust through the roof, pulling up warm dry air to replace it in the process.
     

    Last edited by Hal_S; 07-31-14 at 08:39 AM.
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    Old 07-31-14, 04:55 PM
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    I measured the attic at 100 degrees F. Inside of roof is 105 degrees F. Outside air temperature is 100 degrees F.

    This is with the soffits sealed......

    Seriously guys I think you're giving soffits way too much credit here....they don't do anything....
     
      #29  
    Old 08-01-14, 10:45 AM
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    Any advice? 25char fulfillment
     
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    Old 08-01-14, 01:50 PM
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    What kind of roof do you have ????
     
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