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Old 07-22-2010, 08:36 AM   #1
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Suggestions for attic cooling


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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Old 07-22-2010, 10:34 AM   #2
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Suggestions for attic cooling


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-VE.../dp/B000XZYR4C
http://www.amazon.com/Solar-Attic-Fa...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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Old 07-22-2010, 10:59 AM   #3
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Suggestions for attic cooling


I believe gable vents used in conjunction with a ridge vent can cause the cooling air to "short circuit"
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Old 07-22-2010, 11:01 AM   #4
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Suggestions for attic cooling


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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Old 07-22-2010, 12:42 PM   #5
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If you do add the fascia or In Vent you should seal off the gable vents.
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Old 07-22-2010, 01:01 PM   #6
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Suggestions for attic cooling


Quote:
Originally Posted by Forseti View Post
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.

Last edited by Yoyizit; 07-22-2010 at 01:06 PM.
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Old 07-22-2010, 03:18 PM   #7
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Suggestions for attic cooling


Quote:
Originally Posted by Forseti View Post
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
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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Old 07-22-2010, 03:23 PM   #8
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Suggestions for attic cooling


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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Old 07-22-2010, 06:21 PM   #9
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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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Old 07-22-2010, 07:42 PM   #10
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Suggestions for attic cooling


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Originally Posted by FrankL View Post
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-VE.../dp/B000XZYR4C
http://www.amazon.com/Solar-Attic-Fa...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
GAF now sells dual power attic fans, but they are low flow though.

http://www.gaf.com/Roofing/Residenti...ualPowered.asp
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Old 07-23-2010, 07:42 AM   #11
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Suggestions for attic cooling


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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Old 07-23-2010, 10:04 AM   #12
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Increase your insulation to 20". Install radiant barrier foil .... http://www.atticfoil.com
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Old 07-23-2010, 10:27 AM   #13
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http://www1.eere.energy.gov/consumer...nsulation.html
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Old 07-23-2010, 06:27 PM   #14
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Suggestions for attic cooling


Quote:
Originally Posted by Forseti View Post
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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Old 07-25-2010, 04:39 PM   #15
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Suggestions for attic cooling


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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