Upgraded insulation/seems hotter


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Old 09-19-03, 09:28 AM
Boat
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Upgraded insulation/seems hotter

I just had my attic insulation upgraded to R-30 this past weekend. It may be my imagination, but it seems hotter inside the house now than before. Has anybody heard of that? I live in Lutz, FL (just a few miles north of Tampa).
 
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Old 09-19-03, 10:38 AM
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Yes, this is probably the biggest concern with insulation when it comes to cooling a home. The way insulation prohibits heat flow is by retaining it. This specifically addresses conductive heat transfer. The problem here is in the cooling season, the dominant heat transfer mechanism is radiant. All that means is the hotter an object gets, like insulation, the more heat it will radiate. Though by prohibiting the heat in the attic to conduct into the house is a major concern when dealing with heat gain which keeps the house cool, when you added more insulation to the attic, you created a large enough thermal mass that retained a large amount of heat. It is the heat in this mass that is radiating into your home and causing the discomfort.

I know what you are thinking, why did I ever add more insulation if this is the case? Though radiant heat dominates heat gain in the summer, conductive heat transfer still plays an important role in keeping your house cool in the summer. The thing to remember here is the hotter an object gets, the more heat that object will radiate. So the trick is to not let the insulation retain so much heat.

Now there are a variety of ways to accomplish this, my personal preference is induced convective heat trasfer. What conductive heat transfer states is that air at a lower temperature than the objects, like insulation, it passes over, will extract heat from those objects. Induced means forced, like an attic fan.

In other words, if you installed a thermostatically controlled attic fan, it would force lower temperature air from the outside into the attic. As this lower temperature air passed over the insulation, it would extract heat from the insulation. As you extract heat from the insulation, you diminish its ability to radiate heat. Thereby making the house cooler.

When either heating or cooling a home all three heat transfer mechanisms are present, conductive, radiant and convective. When addressing comfort in your home, the best results are when all three mechanisms are utilized. In other words, not one by itself will produce adequate results.

While some may deduce that the added insulation may have obstructed you eave or soffit vents as the cause, R-30 is a considerable amount of insulation which can retain a considerable amount of heat in the summer. Providing adequate air passage at your eave is prudent, however, considering the amount of thermal mass R-30 insulation possesses, I would still recommend forced attic ventilation.
 
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Old 09-19-03, 03:43 PM
Boat
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Thank you for your advice. Now that you mention it, my husband said that there was an inoperative ventilation fan in the attic. I guess we need to get it working. How much ventilation should there be? I know that at two of the gables, there are vents.
 
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Old 09-19-03, 06:01 PM
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The rule for your application is 1 : 300. That means for every 300 square feet of attic floor area, you need one square foot of free venting. Free venting means that you have an equal amount of high vents to lower vents. High vents are your gable vents, which is probably adequate. Low vents are either eave or soffit vents, which are probably obstructed with the newly added insulation.

Now there are a few ways you can clear the air passage at your eaves or soffit area. The most common is to take a broom stick handle and press down the insulation near the eaves. Sometimes the insulation just expands and obstructs the eave again, but considering that this does not cost you anything other than a little effort on your part, it is well worth it. Another way is to purchase styrofoam baffles which are relatively inexpensive and slide them inbetween the roof decking and the insulation at the eaves. What is nice about this is once this is done, you never have to do it again.
 
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Old 09-20-03, 10:23 AM
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Vents

If you go over to www.lomanco.com there is a lot of good info there on attic vents. ED
 
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Old 09-21-03, 12:46 PM
Boat
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Thank you for all of your advice! I appreciate it!
 
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Old 03-20-10, 03:43 PM
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Do you wear a sweater in August?

Originally Posted by Boat
I just had my attic insulation upgraded to R-30 this past weekend. It may be my imagination, but it seems hotter inside the house now than before. Has anybody heard of that? I live in Lutz, FL (just a few miles north of Tampa).

This is a well kept secret and one actually propagated by insulation manufacturers, lobbyists and electric utility companies that sell energy. Google "adding attic insulation"
Look for a title: "SRP: Questions and answers about attic insulation". SRP is a electric utility in Phoenix AZ. A customer wrote in asking:
" Q: I'm debating whether to add insulation to my attic. My house was built in the early 1970s and is a concrete block home of about 1,300 sq. ft. The concrete block walls are not insulated and do not have drywall on the inside of them. Due to the age of the house and construction of the walls, would extra ceiling insulation be beneficial?

A: Yes, additional insulation would help reduce air conditioning costs while increasing the comfort level inside. Homes built in the 1970s typically had R-19 or R-22 attic insulation. Over time, these levels would be reduced due to settling of the materials.

Of course this is what a power company is going to say, they want to sell more power.

The WORST thing you can do in a hot climate, especially one that has a great deal of solar radiation hitting the roof, is add more attic insulation. But why? Like the title states "do you wear a sweater in August?" Of course not, so why would you think that adding sweaters (fibrous insulation) would make your home cooler?
Fact is this: Fibrous insulation was never designed to keep heat out but rather keep heat in. To prove this, we build two identical 3200 sq foot homes in Phoenix AZ in 1986. Arizona State University did the testing under the guidance of Dr. Byard Wood. One home had R-19 fiberglass in the walls and R-30 blown into the attic. The other house had no insulation and two layers of metalized film in the walls (no insulation), and two layers in the attic. The result? The home with no insulation used 35% LESS energy than the home with insulation. What was really important to note was how long the heat was stored in the insulation after the sun went down, continuing to radiate heat into the home for hours, well past 10pm.

A high profile architect in Sydney Australia added more insulation in her attic and her electric bill went up and her home was miserably hot. A couple in Phoenix was quoted on the news: "We added more attic insulation and our bills went up and our house got hotter". Back in Australia, a Senate hearing on the direction of a mismanaged countrywide insulation program where a homeowner would get $1500 back from the government for adding more attic insulation, provided similar informaion. Dr. Richard Aynsley of the University of Western Australia was quoted during the hearing: "there has been no conclusive evidence that adding more bulk (fibrous), insulation in a hot climate reduces energy use. In fact, it may increase the use of energy to obtain comfort". To which a Senator responded: "How many months has this information been known?" "Months?" replied Dr. Aynsley, "How about decades?"

Put a piece of R-19 fiberglass in your windshield, point your car South and see what happens. This is one of the biggest sources of misinformation and has been propagated for decades by those who would make the most from this misinformation. Or, perhaps you do wear a sweater, jacket, hat and mittens in August in which case non of the above would be relevant.
Solutions? Proper attic venting is a start and if you live in a hot climate the building code for venting is NOT for heat removal but rather moisture egress. Homes in hot climate need at least FOUR TIMES what is recommended by code. Intake vents around the perimeter (that are not blocked with insulation), and exhaust vents place high on the roof peak. Especially in a hot climate adding a multi-layered, dust proof radiant barrier would make a significant impact.

End note: On attic venting, stay away from Home store fans made in China the are over rated, catch on fire, vibrate, have cheap inaccurate thermostats (stick on or stick off), and have bushings not sealed bearings...total waste of time. Even worse are the solar powered attic fans. 10 watt, 20 watt, or the "Super Powerful" 30 watt fans are grossly over rated (claim "up to 1200cfm, actual is 310cfm), have motors with brushes (last two years), bushings, not rated for attic temperatures and underpowered. Google "attic venting" and look for better stuff.



 

Last edited by savenrg; 03-20-10 at 04:50 PM. Reason: Forgot to add something relevant to the reply....thanks
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Old 03-21-10, 06:35 AM
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Old 03-21-10, 08:24 AM
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Original post is 6 1/2 yrs old.......please check dates..thx
 
 

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