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litespeedrider

07:10PM | 04/04/05
Member Since: 04/03/05
1 lifetime posts
Bvroofing
Our roof was recently destroyed in a hail storm. It was suggested that we replace the 2 turbine vents with ridge vents for increased energy efficiency. We live in south Texas and from June through mid-September the afternoon temperatures are in the upper 90's and often over 100 in July and August.

Would we see a reduced cost for cooling if we use the ridge vents instead of turbines?

Are there any problems with ridge vents that we need to be aware of?


dodgeroof

02:53PM | 04/05/05
Member Since: 03/27/05
95 lifetime posts
You might see a reduction in cooling costs. Ridge vents will vent the attic more thoroughly, but only work as well as the amount of air intake you have through the soffits.

You also want to make sure you have adequate attic insulation or you could end up paying more in the winter for heating costs due to heat loss due to an improved ventilation system.

Or maybe you guys in Texas don't have heating costs in the winter:}

A roof CAN be your friend

bravey

10:15PM | 04/06/05
Member Since: 06/23/04
161 lifetime posts
I live southeast Texas and have similar heat levels to contend with. When you live this far south, attic ventilation takes on a whole new complexion. Further north, attic ventilation is primarily for moisture control and to a lesser degree heat evacuation. When the temperatures hover between 95 and 105 for weeks on end, the levels of ventilation used in northern climes don't cut the mustard. If you investigate houses built before the common use of air conditioning you will find larger eave vents (huge by todays standards) and large gable vents which moved much more air volume than turbine vents or ridge vents. Two basic principles to remember when dealing with large scale heat removal are 1) the more air removed, the more heat removed (when you sweat do you cool down faster with a light breeze or a gale?) and 2) larger openings move more air.

As an example, take a 1500 sf house 25' x 60' with a 6:12 gable roof 60' long. The attic volume is about 4700 cubic feet.

Assume the house to be fitted with three turbine vents on the roof and 30 soffit vents (4' centers both eaves). The soffit vents let in the cooler air and the turbine vents let out the heated air. A 12" base dia. turbine vent is 0.78 sf x 3 each = 2.34 sf. The soffit vents are usually 4"x10" (or smaller) stamped vents with about 25% free area which, for 30 vents, translates to 2.00 sf. The smaller of the two areas is the controlling opening size. Thus there are 2 sf of area to ventilate 4,700 cubic feet of attic. If the heated air is moving at the velocity of 2 feet per second (generous) the system will remove 240 cfm of air. With the attic volume of 4,700 cf divided by 240 cfm, it will take 19.58 minutes for one air change (3 air changes per hour). That is not going to cool the attic very well.

Ridge vents advertise openings of 12 to 20 square inches per linear foot. Converting, 20 si = 0.139 sf x 60' =8.33 sf for the entire ridge. That is nearly four times the area of the 3 turbine vents! Remember, equally large (or larger) soffit vents areas must be provided to supply the air for the ridge vents.

Traditional gable vents are 10' to 12' long with about 60% free area which calculates out to 21.65 sf per vent. With one vent at each end of the roof you have 43.3 sf of vent area. That is FIVE times greater than the ridge vent. NOW we are moving some air and heat!

To cut costs, builders have been installing ever smaller vents until, in the past decade, many houses have been built with no vents at all. In the 80's and 90's many builders used 2" dia. aluminum disk soffit vents with stamped slots totalling 0.5 square INCH of area. At every 4 feet that would be 0.10 sf for the whole house! That is so insignificant as to be criminal.

If you want to cool your house, install anything you like as long as it has large FREE area to pass large volumes of air. Don't be taken in by slick advertising. Remember that FREE area is much less than the NOMINAL size of the vent. What works ok in Illinois isn't necessarily sufficent for south Texas. Learn from the old homes in your area (1800's-1940's). They HAD to have better ventilation, wereas we just let the AC run longer.

Also remember that building codes in Texas now establish minimum ventilation standards. Note the word MINIMUM. This does not mean that the sizes required are high performance, it means that they are the LOWEST that the code will allow.

Regards

becknsteve

04:10AM | 03/15/07
Member Since: 03/04/07
2 lifetime posts
your post was extremely helpful. I have a 1920's vintage home in Wichita,Ks and am putting in two gable fans for circulation. Yes, the gable openings are huge compared to more modern homes and that makes air movement much easier, but are there any rules of thumb as to fan positioning for maximum efficiency. My home has an east-west ridge line with multi level gables. Two gables are on the prevailing wind side and one on the opposite side.. any ideas or suggestions?

OddBall

02:47PM | 03/19/07
Member Since: 11/10/06
138 lifetime posts
If you want to use gable vents, you need wind or power fans otherwise the air don`t flow !! It also creats a horizontal vortex that mixes the air rather than move it !!

The installation of ridge vents combined with prop vents and soffit vents allows the rising of heat to drive, the soffit vents will intake and the prop vents on the rafters, allows your option to put a finished cieling for your loft room !! Wind is not an issue !!

If you have small crawl space,...same applies without the finished room !!

Ridge venting creats a vertical vortex, without wind, still moves air.

Consider: When the fire dept. goes to your house the first thing on their mind is occupants, then heat consentration in the attic along the ridge peak. that`s where they make the vent holes.

The New England Shakers, useually built Colonial style homes with the stairs in the center of the house from the basement to the attic. A coopular box vent was put on the roof atop the stairwell. (size depended on size of home or numbers of coopulars)

A oil powered chandelare was put atop the stairwell. The windows on the second and or third floor were closed. Only the windows on the first floor were left open a few inches. When the lanterns were lit in Summer, the heat rose up threw the coopular, drawing the air in the first floor windows. The size of the flame on the candles dictated the speed of the draft created by the chimney effect. This draft can be measured by a wind speed indecator. Sometimes enough to put out the candles !!

Just some quick input,....when I have time I`ll get more detailed for ya !!

OddBall,...30 yr. roofing !!

becknsteve

06:10AM | 03/25/07
Member Since: 03/04/07
2 lifetime posts
Thanks for the input! I really appreciate your experience here, and I need to give more details. This house doesn't have any soffet vents and none to add yet due to its original design and the cost involved. The original roof was removed last summer four static vents put (in where there were none before) on a roof with a 10/12 pitch. This is an older house with lathe and plaster throughout so very little insulation exists. Air movement through the attic is my primary concern at this time There was no ridge vent installed either, however this may be necessary at some time in the future as you advise. Cooling in Kansas is primary due to our climate, and any further input is still greatly appreciated.

2to4GSRB

08:19AM | 02/03/10
Member Since: 11/01/09
4 lifetime posts
In a post called, Attic Vnetilation, on 04/07/2005, bravey said the following:

"... A 12" base dia. turbine vent is 0.78 sf x 3 each = 2.34 sf. The soffit vents are usually 4"x10" (or smaller) stamped vents with about 25% free area which, for 30 vents, translates to 2.00 sf. ..."

Since "free area" (or Net Free Area, NFA) is only mentioned regarding the soffit vents, the implication is that the 2.34 sf for the turbine vents is their NFA, & the NFA for one such turbine vent is 0.78 sf. Is this true / a fact?

alabama homeowner

12:50PM | 02/13/13
Member Since: 02/13/13
1 lifetime posts
I am replacing the roof on my 1950's one-story house near Birmingham, AL. The house is situated on the edge of a north-facing ridge line, and there is a nearly continuous flow of air coming up the ridge, with the direction of flow changing from northerly to southerly according to weather conditions. In my carport, located at the east end of the house, there is nearly always a strong breeze. I'm trying to decide if I should change from the current system of two wind turbines on the roof (almost always in motion) to a ridge vent system, and if so, should I have any concern about a wind baffle for the ridge vents, given the strong flow of air at my home site. At present, there are three 12x12 inch soffit vents under the eaves on both the front and back of the house. Do I need to add more soffits for the wind turbines? For the ridge vent system? I should mention that I rarely use air conditioning in the summer, as the french doors to the north-facing deck stand open, and open windows on the front of the house create a good breeze. I'd like to make sure my attic is adequately ventilated, with the least amount of cost. Thanks.

BV001721

11:33AM | 08/01/13
Is 8' of ridge vent adequate for a standard size free standing 2 car garage? My roofer says that is all that is needed.

BV002774

12:11PM | 12/11/13
I just want to chime in here regarding the "up north" and "moisture control" by way of using ventilation. You want to control the moisture before it reaches the attic. Looking to ventilation to control moisture in an attic is like handing you a pail on a sinking ship with a gaping hole in it. Either fix the problem or move out. Ventilation is often used as an answer to attic mold issues up north. We get the calls when it does not work. I am starting a new discussion (hopefully) regarding a new term: "CEILING ENVELOPE" as a play on the overused and abused "building envelope" discussion which I see as a refuge that is being used by those that are looking for an answer to the interior moisture problems. The thinking is usually that moisture emanates from without but often moisture originates from within a structure. Then condensation occurs because of improper handling of interior moisture. Channeling moisture into an attic and expecting vents to carry it out is really a ridiculous idea that has been fostered by manufacturers of roofing products that require venting to cool vulnerable fiberglass based, less malleable asphalt products.
Moldy4
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