# Suggestions for attic cooling



## Forseti (Jul 22, 2010)

Hi all,

I have an older (1967) 1 story rancher in Maryland. We just had the a/c unit for the house replaced, and during that ordeal I found out a bit about our attic:

1) It's about 150 degrees up there on a hot summer day
2) Previous owner only had 2" of insulation installed
3) Currently the attic has two high gable vents, a ridge vent, and an electric vent on the back of the roof
4) Soffits on most of the house appear to be too small (5") for soffit vents. The front of the house has appx 2' of overhang


I'd like to increase airflow, and take steps to prevent heat transfer in the summer and heat loss in the winter. 

I figure that I should install a ton of insulation. Beyond that, What would you all suggest that I do? 

I was thinking of installing thermal barrier attached to roof joists? Or adding more ways to vent?

Thanks for the help


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## FrankL (Jun 9, 2010)

Search around on the internet but you can find solar power roof vents or search solar attic fans. You can get a tax credit. They are not cheap but not that expensive either. 

http://www.atticbreeze.net/
http://www.solardynamicsinc.com/
http://www.amazon.com/SOLAR-POWER-VENT-ROOF-MOUNT/dp/B000XZYR4C
http://www.amazon.com/Solar-Attic-Fan-25-year-Warranty/dp/B0002YWVJM/ref=pd_sim_dbs_e_4

There are a bunch more. It seems like $250 is an avg price. I am not sure what the tax savings are. It seems like a good idea. I am not sure if they can move enough air. 

_"Moving over 1550 CFM of air"_ 

That seems like a lot of air. 

Frank Lardino


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## Joe F (Jan 27, 2008)

I believe gable vents used in conjunction with a ridge vent can cause the cooling air to "short circuit"


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## justintime08 (Nov 14, 2008)

In lieu of soffit vents you can install fascia vents or the In Vent which is a roof top vent. Check out the products listed on Coravent's website.


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## justintime08 (Nov 14, 2008)

If you do add the fascia or In Vent you should seal off the gable vents.


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## Yoyizit (Jul 11, 2008)

Forseti said:


> Currently the attic has two high gable vents, a ridge vent, and an electric vent on the back of the roof


For fan CFM vs. attic volume, the volume for a gable roof is HWL/2, where H & W are the gable height and width and L is the roof length. A 3' high gable 28' wide on a 32' roof should be 1344 cu. ft.
Above 30 air changes per hour is probably not worth it, especially at our latitude.


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## seeyou (Dec 12, 2008)

Forseti said:


> Hi all,
> 
> I have an older (1967) 1 story rancher in Maryland. We just had the a/c unit for the house replaced, and during that ordeal I found out a bit about our attic:
> 
> ...


Installing more insulation and air sealing any penetrations from the living space to the attic will give the best results. It sounds like you probably have enough venting. If it's 100 degrees outside, it doesn't matter how much venting you have, it's never gonna get below 100 in the attic. Stop that heat from radiating through to the living area.


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## Thurman (Feb 9, 2009)

For What It's Worth: I had a new roof installed (not roof-over) three (3) years ago with brand new ridge vents. I have a gable roof home with vents. Just to see, I kept a check on the attic temps and did find the attic was hotter with the new ridge vents _and _the gable vents with one gable vent having an automatic fan. Maybe short-circuiting air. I closed off the gable vents with some exterior foam sheathing with foil backing. I changed the fan to one a "squirrel cage type" that came from an old A/C split system, it hangs 18" from the roof peak, is on a thermostat, and is now ducted to the ridge vent along a 10' length, and the attic is much cooler. I bought a smoke bomb for detecting air movement fro a local Safety Supply Store and found that the air is indeed moving from the soffit vents up to the fan and out via the ridge vents. Maybe a little over-kill but it works. Sometimes innovation is the key to solving problems, to me at least. David


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## justintime08 (Nov 14, 2008)

By currently having the gable vents sealed and having a ridge vent for exhaust you have created a situation in which you are going to be exploiting any tiny leak you have from your conditioned areas. This means that because the ridge vent can not pull air from a proper intake vent it will pull it from any other little openings to your conditioned spaces.


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## handy man88 (Jan 23, 2007)

FrankL said:


> Search around on the internet but you can find solar power roof vents or search solar attic fans. You can get a tax credit. They are not cheap but not that expensive either.
> 
> http://www.atticbreeze.net/
> http://www.solardynamicsinc.com/
> ...


GAF now sells dual power attic fans, but they are low flow though.

http://www.gaf.com/Roofing/Resident...wered/MasterFlow-GreenMachine-DualPowered.asp


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## Forseti (Jul 22, 2010)

Thanks for all the replies. Yesterday I went back up into the attic (after sundown) to reassess the situation. 

I've definiately got a problem... A smoke test showed that air is coming in through the ridge vent and exiting via the power fan.  So I definitely need to fix that (on top of everything else). I wish the roofers would have informed me of the issue when I had the new roof put on a few years ago.

There are also MAJOR gaps around pipes and our 2nd access panel.


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## igneous1 (May 6, 2010)

Increase your insulation to 20". Install radiant barrier foil .... http://www.atticfoil.com


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## Yoyizit (Jul 11, 2008)

http://www1.eere.energy.gov/consumer/tips/insulation.html


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## handy man88 (Jan 23, 2007)

Forseti said:


> Thanks for all the replies. Yesterday I went back up into the attic (after sundown) to reassess the situation.
> 
> I've definiately got a problem... A smoke test showed that air is coming in through the ridge vent and exiting via the power fan.  So I definitely need to fix that (on top of everything else). I wish the roofers would have informed me of the issue when I had the new roof put on a few years ago.
> 
> There are also MAJOR gaps around pipes and our 2nd access panel.


What happens when the power fan is turned off?


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## hereslookingatU (Feb 8, 2010)

Hi

Sounds like your building might be a candidate for some sustainable initiatives: e.g. Solar Thermal - to heat the water in your home and maybe PVs to provide some background electricity?

Why? Well one of the issues you have is solar gains into the attic and if you want to cure this you need to stop the solar gains entering the roof structure and if you clad part of the roof with solar thermal panels you will reduce the amount of solar gains while at the same time heating the domestic hot water. 
You don't want to cover the whole roof in solar thermal panels otherwise you will end up having more hot water than you can use and you will then need to find a way of dumping the excess heat! Secondly add some PVs to cover a larger area of the roof. Both these initatives have the benefit of shading the roof (thereby reducing solar gains and making the loft cooler.)

Next issue is the amount of insulation - the type of insulation you use will dictate the thickness that you require, for example with PIR (foam) Insulation the cost benefit starts to become insignificant after around a thickness of 4". To install the material you would generally put 2" between the rafters (to maintain an air gap between the insulation and the roof covering thereby allowing the roof structure to breathe; and 2" over the face of the rafters (this would normally be a composit material with a plasterboard finish - but it does not have to be! Just depends on the finish that you want!) The extra insulation will also assist in reducing incoming solar gains, while retaining heat in the building in the winter months.

Regards


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## Gary in WA (Mar 11, 2009)

So it sounds as if the air handler is in the attic, along with the ductwork? http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

Be safe, Gary


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## Deckmaster (Jul 15, 2009)

Even with proper venting and insulation a radiant barrier is a great idea especially on an older home. Check out Enerflex radiant barrier, I saw it in Money Magazines energy section last week. Suppose to decrease attic temp by 30 degrees. Seems pretty simple to install. link to a you tube video http://www.youtube.com/watch?v=EDfUW1dGBGE


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## matrixman (Sep 14, 2010)

Deckmaster said:


> Even with proper venting and insulation a radiant barrier is a great idea especially on an older home. Check out Enerflex radiant barrier, I saw it in Money Magazines energy section last week. Suppose to decrease attic temp by 30 degrees. Seems pretty simple to install. link to a you tube video http://www.youtube.com/watch?v=EDfUW1dGBGE


 After watching that video something tells me that can't be good for the life of the shingles. Sounds like it would cook the shingles which would lead to shorter shingle life.


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## Deckmaster (Jul 15, 2009)

*Radiant Barriers and Roof Shingle Temperatures*

According to the Reflective Insulation Manufactures Association's independent study, a radiant barrier may cause an increase in shingle temperature between 2-5 degrees Fahrenheit on a hot summer day. Given that shingle temperature at that time is in the range of 160-190 degrees, this increase is negligible and does not accelerate shingle degradation. Although roofing manufacturers were concerned about shingle failure in the years when radiant barriers were first used, it is no longer an issue. Roofing material warranties are not affected by the installation of radiant barriers.

Read this roof shingle temperature study for more details.
http://www.rimainternational.org/technical/tb103.html

The Florida Solar Energy Center also conducted a study on the use of radiant barriers under shingle roofs and found that properly installed radiant barriers do not void the warranty for the shingles.


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## FrankL (Jun 9, 2010)

As far as solar power, it appears you can do hot water heating and maybe an attic fan. Do any of the solar systems generate enough power to drive air conditioning during the day? I assume you would have to be on a separate circuit. 

Frank Lardino


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## Deckmaster (Jul 15, 2009)

Solar powered attic fan, proper insulation and a radiant barrier are all a great start.

There are solar powered 240 W AC units, but unfortunately initial price is high ranging from $10K to $20K depending on size. Than again, if your energy bill is $800 a month it may be worth the investment. http://www.solarac.com/

My suggestion is to add a radiant barrier and solar attic fan (make sure you have enough insulation too), see how much your AC/electrical bill shrinks (I've heard some save over 50%) then decide whether your want a solar AC unit.

I know Enerflex Radiant Barrier also qualifies for a tax credit. http://www.enerflexfoil.com


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## Gary in WA (Mar 11, 2009)

Before purchasing a radiant barrier, check your savings, if any, as it depends on location: http://www.ornl.gov/sci/roofs+walls/radiant/rb_02.html

http://www.advancedenergy.org/build...entilation/Attic Ventilation Case Studies.pdf

http://www.ronhungarter.com/black_mold.html

Gary


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## Deckmaster (Jul 15, 2009)

You will save using a radiant barrier, no question.
Your savings on heating and cooling bills will vary, depending on many factors. Savings will depend on the type of radiant barrier application, the size of your house, whether it is a ranch style or a two story house, the amount of insulation in the attic, effectiveness of attic ventilation, the color of the roof, the thermostat settings, the tightness of the building envelope, the actual weather conditions, the efficiency of the heating and cooling equipment, and fuel prices. http://hvac-talk.com/vbb/showthread.php?p=7853862


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## Gary in WA (Mar 11, 2009)

Ahhh. You work for them. 75% of your posts push radiant, and your sales pitch is showing. 

OP, savings may be minimal and you may *lose the shingle manufacturers warranty*. The savings might better be used to seal any attic air leaks, add a balanced ventilation system, or just add more insulation to the minimum suggested R-value for your location. http://www.ornl.gov/sci/roofs+walls/radiant/rb_tables.html#table4

“Reflective barriers are not generally considered a good application in houses
located in climates *where heating is dominant*.” --------- from: http://www.energyideas.org/documents/factsheets/PTR/HeatTransfer.pdf

 I could see *radiant in Zones 1, 2, and parts of 3*; check your location and heating degree days: http://www.nrel.gov/docs/fy00osti/26450.pdf

If you get snow, adding radiant rather than more insulation or sealing air leaks and you may get ice dams: http://www.buildingscience.com/documents/digests/bsd-135-ice-dams

Gary


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## federer (Aug 20, 2010)

love your thoroughness GBR


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## Deckmaster (Jul 15, 2009)

Yes, I work for NASA where we invented radiant barriers. We use radiant foil suits on the space station and on our suites merely because they look cool not because they reflect heat. 

*House Shingles*
Apparently you didn't read the info from RIMA and FSEC.
Read this roof shingle temperature study for more details.
http://www.rimainternational.org/technical/tb103.html

The Florida Solar Energy Center also conducted a study on the use of radiant barriers under shingle roofs and found that properly installed radiant barriers do not void the warranty for the shingle

Part of your post is accurate in that a radiant barrier is most effective in Southern regions where it is typically hot not cold. A radiant barrier is great for the heat, but insuilation is the first go to in the colder climates (half as effective).


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## matrixman (Sep 14, 2010)

Deckmaster said:


> According to the Reflective Insulation Manufactures Association's independent study, a radiant barrier may cause an increase in shingle temperature between 2-5 degrees Fahrenheit...


Not sure I am going to take my research from an association that can monetarily benefit from this "study". There are always ways to rig a study.


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## matrixman (Sep 14, 2010)

Deckmaster said:


> Part of your post is accurate in that a radiant barrier is most effective in Southern regions where it is typically hot not cold. A radiant barrier is great for the heat, but insuilation is the first go to in the colder climates (half as effective).


I hear the same things that it is better suited for places like Arizona and Florida. Hot and Humid.

Saw this, they claim its good for winter as well since it traps the heat.

RBS Chips: 
http://www.savenrg.com/1rbschip.htm 
http://www.savenrg.com/winter.htm 

From site:



> If you live in a cold climate and really want to mpact our heating bills, and make your home warmer in the winter and cooler in the summer, then consider installing Barrier System Chips (RBS Chips)
> 
> Keeps heat in during winter, out during the summer
> Lifetime performance warranty (over 20 years of installations)
> ...


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## matrixman (Sep 14, 2010)

Deckmaster said:


> My suggestion is to add a radiant barrier and solar attic fan (make sure you have enough insulation too), see how much your AC/electrical bill shrinks (I've heard some save over 50%) then decide whether your want a solar AC unit.


I ended up buying this today after much research on solar attic fans:
*Attic Breeze Zephyr AB-252D-GRY*

I like:
American made
Lifetime warranty
higher 25W better type monocrystalline solar panel
sealed bearings
weatherproof metal
14" fan blade
1550 CFM

Of course manufactured in USA means alot of things to different marketing folks, so I still have an email into them on if they use all american parts.

One fan will cover my 1925 sq. ft. on an 8/12 weatherwood colored roof.


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## federer (Aug 20, 2010)

thanks for the update. let us know how it goes


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## Gary in WA (Mar 11, 2009)

And that’s not all the chips trap: “A radiant barrier installed on top of attic floor insulation is more susceptible to dust accumulation. This undesirable installation method may also trap moisture in fiber insulation during cold weather. A radiant barrier installed on the cold side of the insulation acts as a vapor barrier in the wrong location. When warm moisture carrying house air leaks into the attic in the winter, it may condense on the underside of the barrier. Even a perforated radiant barrier can trap moisture in cold climates since the water can freeze in the small holes and seal them. Because of these hazards, it's strongly recommended that you NOT apply radiant barriers directly on top of the attic floor insulation. Of course, installing them at all in a cold climate is not generally cost effective anyway.” From: http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11680

Also: http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11680

They also trap dust: “When the radiant barrier is placed on the attic floor, dust does become a problem. As dust builds up, insulating value is reduced by as much as half, over a period of *one to ten years*.” From: http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/92/920704.html

If you have gas units, be careful: http://www.advancedenergy.org/build...entilation/Attic Ventilation Case Studies.pdf

Your attic fan could pull conditioned air from the living space below unless you air sealed first: http://www.rd.com/how-to-seal-attic-air-leaks/article18158.html

It will also short circuit any gable or ridge vents, negating the soffits as intakes.

Gary


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## Deckmaster (Jul 15, 2009)

A radiant barrier should not be in contact with the floor insulation. It will lose its effectiveness as dust collects or if in contact with virtually any othre surface, that's why it's recommended to be installed on or between the roof joists and on all vertical / gable ends. 

If installing on your bottom insulation, your attic will still heat up because it's allowing the sun's radiant energy to penertrate into the attic space.


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## Gary in WA (Mar 11, 2009)

This seems typical of most salesmen:* don't listen*, just run your spiel. The original poster (almost two months old, usually means resurrected by a product ad) lives in Maryland, where a radiant barrier would not be positive, but negative: http://www.inspectapedia.com/Energy/Radiant_Barriers.htm

Read my last post again, slowly- notice the word “chips”? 

Read post #28 again- or first time……… 

I know where radiant works, NOT always with gains as you said: “You will save using a radiant barrier, no question.” I feel sad that you believe this lie enough to tell it to others. Tell them the other side of the story, you can reap *negative numbers*.

Some areas will* lose* money installing it rather than more insulation in a colder climate. Your pitch is almost as bad as fiberglass insulation’s. (I've heard some save over 50%)

Gary


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## Deckmaster (Jul 15, 2009)

Thanks for the kind words Gary, but I don't sell. You really haven't done your research on this topic, and it's clear. Radiant barrier will work in virtually any climate and obviously in the hot climates your payback period is much shorter than in the cold climates. Radiant barriers work both ways: keep hot out in the summer and retain heat in the winter. Like I said, choose proper insulation in the cold climates first. Regardless, live green.


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## Gary in WA (Mar 11, 2009)

I did some more research. 

I knew that radiant barriers work best in warmer climate areas, reducing the cooling load and don’t affect the heating load, other than negating it. In the winter, you need the heating effect of the sun in the attic, not block it.
So if one has minimal insulation with more heating days than cooling (using the AC), it is more cost effective to add more insulation than a radiant barrier. 

“Radiant barriers are more effective in hot climates than in cool climates. Some studies
show that radiant barriers can lower cooling costs between 5%–10% when used in a
warm, sunny climate. The reduced heat gain may even allow for a smaller air conditioning system. But in cool climates, it's usually more cost effective to install more than the minimum recommended level of insulation rather than a radiant barrier.”--- http://docs.google.com/viewer?a=v&q...pnJuQ_&sig=AHIEtbQqrIgmkhZbubw3EezxxzJ6a8AaeA

“The best application of radiant barriers is when the house is in a climate which needs cooling and has either the air conditioner or ducts in an unconditioned attic.” --- The sheets are a plus here but not the chips or the paint: http://www.recurve.com/your-home/building-basics/radiant-barrier/

” Our survey simply shows how the two systems performed compared to one another. This comparison also makes it obvious that, even in Louisiana’s mild climate, some type of insulation is needed.” http://www.healthyheating.com/Page 55/Downloads/Insulation_Comparison_Demonstration.pdf
That is the fifth one down from here: http://www.healthyheating.com/Page 55/Page_55_o_bldg_sys.htm

Gary


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