Seal Gable Vents After Ridge Vent Installed?

tacoma5050 · 08-31-2007, 12:27 PM

I just replaced a roof with 30yr asphalt fiberglass shingles. Previously there were only gable vents and the customer wanted a ridge vent so I installed one. There are only three small soffit vents, so I will be adding soffit vents at each rafter spacing.

Someone suggested that once there is proper soffit ventilation and a ridge vent, that I should seal off the gable vents. The therory being that the gable vents will disturb or decrease the disired air flow from the soffit vent to the ridge vent, or that the ridge vent will pull more air from the gable vent then from the soffit vent. I would assume that we want the gable vent to pull most air from the soffit vent and not the gable vent.

Any comments? Thanks....

The house is a 2 story colonial in the northeast with a walkable pitch.

**Ed the Roofer** · 08-31-2007, 01:01 PM

[quote=tacoma5050;282597]

I would assume that we want the gable vent to pull most air from the soffit vent and not the gable vent.

quote]

I presume that you meant to say Ridge Vent to pull most air from the soffit vent and not the gble vent.

Please download the free ventilation publication from Air Vent Corporation, entitled "The Principle Of Attic Ventilation", which will be a constant source of information for you, and you can even order the printed booklette for free.

Yes, according to proper air flowage dynamics, the gable vents should be sealed off so as to not "Short-Circuit" the attic ventilation flowage.

Ed

tacoma5050 · 08-31-2007, 02:36 PM

Hi Ed,

Oops, yeah I meant to say: "we want the Ridge Vent to pull most air from the soffit vent and not the gable vent."

Thanks for the info and the answer to my question.

I found the doc you referenced here:
www airvent com/professional/resources/literature.shtml
(the forum won't let newbies post URLS)

thanks...

[quote=Ed the Roofer;282603]

Quote:

Originally Posted by tacoma5050

I would assume that we want the gable vent to pull most air from the soffit vent and not the gable vent.

quote]

I presume that you meant to say Ridge Vent to pull most air from the soffit vent and not the gble vent.

Please download the free ventilation publication from Air Vent Corporation, entitled "The Principle Of Attic Ventilation", which will be a constant source of information for you, and you can even order the printed booklette for free.

Yes, according to proper air flowage dynamics, the gable vents should be sealed off so as to not "Short-Circuit" the attic ventilation flowage.

Ed

Tom R · 08-31-2007, 07:42 PM

One time I did an addition on the back of a rancher, - - the main house had gable end-vents, - - but my addition had soffit and ridge vents. I reverse-gabled the (fairly low-pitched) addition onto the existing roof. I installed cobra ridge vent and shingled the roof. And at some point I cut a hole through the existing (now covered part of the) roof for attic-access from old to new.

Anyway, - - that night it snows and when I show up in the morning, - - there was a straight line of actual snow on the subfloor directly below the ridge vent

Turned out I finally figured out the gable vents combining with the ridge vents were creating a reverse air-flow and actually drawing the snow 'into' the building.

I installed a (removable) cover over the access-hole, - - and no more leaks ever again . . .

PlainPainter · 08-31-2007, 08:38 PM

This begs the question - if a building has already gable vents - is there a real need for ridge vents? Perhaps this is before the practice of insulating an attic - where as now if an attic is insulated, you still want a flow of air between the insulation and roof decking. And if the attic is insulated - if you cut off the gable vents - the space is no longer ventilated - so it might be you want both in those circumstances.

dennis · 08-31-2007, 10:43 PM

I will have to respectfully disagree with ed's reply. Unless your house looks exactly like, and the air flow dynamics are the same, as the one on the airvent site. I think there are too many variables for a simple solution.

My reasoning is explained here http://roofersreview.com/Ventilation

and here http://roofersreview.com/htmlpage2

**Ed the Roofer** · 08-31-2007, 10:59 PM

Dennis,

Do you have any references to supply to validate your hypthesis?

Are there any actual wind flowage studies you can cite to back up the illustrations you linked to?

Doesn't the following quote from Toms previous post depict a real life scenario and the obvious conclusions?

Quote:

I installed cobra ridge vent and shingled the roof. And at some point I cut a hole through the existing (now covered part of the) roof for attic-access from old to new.

Anyway, - - that night it snows and when I show up in the morning, - - there was a straight line of actual snow on the subfloor directly below the ridge vent

Turned out I finally figured out the gable vents combining with the ridge vents were creating a reverse air-flow and actually drawing the snow 'into' the building.

I installed a (removable) cover over the access-hole, - - and no more leaks ever again . . .

I am not saying that I believe everthing that Air Vent and other ventilation manufacturers force feed us contractors, but I am always willing to explore new theories with proper back up data.

A real life example such as the one listed and many I have observed personally for nearly 30 years of roofing and studying my craft extensively tend to persuade me otherwise from your conviction.

Ed

dennis · 09-02-2007, 12:37 PM

Hi Ed,

Here are some of the sources I have found.

http://www.upea.com/winter/Influence%20of%20climate.pdf
http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc38715/
http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc38517/
http://www.fpl.fs.fed.us/documnts/pdf1999/tenwo99a.pdf
http://www.agresearchforum.com/publi...5/100_page.pdf

There are a lot more if you google “wind flow over a building“ and “computational fluid dynamics” etc.
Do you have any specific questions about my ideas or items on the webpages that I could maybe try to explain better? Is there something you see there that doesn’t look right?
If you know of any studies or sources to refute my ideas I would be happy to read them.

Quote:

Doesn't the following quote from Toms previous post depict a real life scenario and the obvious conclusions?
Quote:
I installed cobra ridge vent and shingled the roof. And at some point I cut a hole through the existing (now covered part of the) roof for attic-access from old to new.

Anyway, - - that night it snows and when I show up in the morning, - - there was a straight line of actual snow on the subfloor directly below the ridge vent

Turned out I finally figured out the gable vents combining with the ridge vents were creating a reverse air-flow and actually drawing the snow 'into' the building.

I installed a (removable) cover over the access-hole, - - and no more leaks ever again . . .

Anecdotal evidence. Was the ridge vent installed correctly? Was the ridge vent poorly designed?

“Anyway, - - that night it snows and when I show up in the morning, - - there was a straight line of actual snow on the subfloor directly below the ridge vent

Turned out I finally figured out the gable vents combining with the ridge vents were creating a reverse air-flow and actually drawing the snow 'into' the building.”

The snow was directly under the ridge vent. Does that mean that the gable vents were pulling air from the ridge vent? Should he scrap the ridge vent?

“I installed a (removable) cover over the access-hole, - - and no more leaks ever again . . .”

Does that make any sense to you?

Looks like we got about the same amount of time in this game. I was picking nails and shingle pieces out of bushes when I was thirteen.

**Ed the Roofer** · 09-04-2007, 09:51 PM

Thanks for the links Dennis. I will copy them and read through the information later this week when I have more time.

I do have a particular insight into some additional air dynamics testing results from an intake ventilation manufacturer which surprised him about the water flowing upwards under the shingles, but I am awaiting the hard copy of the reports from an independant testing laboratory first, so I can draw my own conclusions.

I was involved very deeply in another forum with many pros and cons being brought forth which each had their own merits.

Sometimes, you can only decipher all of the scientific mumbo-jumbo so much, and then go to work doing what is commonly accepted.

Ed

theroofinggod · 09-06-2007, 01:08 AM

"on the road again"eh dennis

--you are untiring in this pursuit,my info agrees w/ ed,Tom r apparently didn`t nail the ridge vent down well before capping it,1st time I`ve heard of that

dennis · 09-06-2007, 07:35 PM

theroofinggod.

I would be happy to look at "your info". Can you direct me to the scientific information that supports your ideas?

**Ed the Roofer** · 09-07-2007, 01:26 AM

Dennis,

Read page 17 of the following link regarding gable vents.

http://www.osti.gov/energycitations/...e/10186298.pdf

The following descriptions of passive venting strategies are based more on anecdotal

evidence and a consensus of practitioners than on actual measurements (see Forgues,

1985 for a more detailed discussion of attic venting strategies):

" Gable vents":

Usually consisting of a set of horizontal louvers shaped to discourage
the entrance of precipitation, are installed on vertical surfaces in the attic. They
can provide high flow rates but depend strongly on wind direction. They are
inexpensive and are often the only existing ventilation, however they do not
usually provide good air flow at lower portions of the attic unless combined with
soffit vents. They do not get covered with snow but may allow entry of wind driven
snow in some circumstances if not properly re-designed when installed
(some contractors fasten a thin layer of fiberglass over the opening and fabricate
a drip tray with flashing in order to avoid snow entry). Contractors report
commonly finding plastic over gable vents installed by homeowners to solve this
problem.The large air flows through gable vents have also been reported to

create suction at roof louvers and thus draw snow into the attic.

Ed

**Ed the Roofer** · 09-08-2007, 05:39 PM

Dennis,

I thought you might find this older paper useful too.

http://irc.nrc-cnrc.gc.ca/pubs/bpn/57_e.pdf

Ed

**Ed the Roofer** · 09-08-2007, 05:45 PM

Here is another paper stating proper requirements.

This is the link for this paper:
http://ct.gov/dps/lib/dps/office_of_...07/i-11-07.pdf

Ed

STATE BUILDING CODE INTERPRETATION I-11-07

April 9, 2007

The following is offered in response to your request for an interpretation of the provisions of Section 1503.5 of the 2003 International Building Code (IBC) portion of the 2005 State Building Code.

Question:
When re-roofing a building that has existing gable end louvers for attic ventilation, can one add ridge vents without adding soffit vents and disabling the gable end louvers?

Answer:
No. Section 1503.5 of the IBC states, in part, that roof intake and exhaust vents shall be installed in accordance with the manufacturer’s installation instructions. A review of a variety of manufacturer’s installation instructions as well as several ICC evaluation reports for ridge vents indicates that in all cases reviewed the ridge vents are intended to be installed in conjunction with eave, cornice or soffit vents. The combination of low intake vents at the eave, cornice or soffit, and high exhaust vents at the ridge promotes uniform ventilation of the entire attic space based on cooler air entering at the low vents and warmer air exhausting at the high vents. Gable end louvers, while not as efficient as a combination low and high system, likewise promote uniform ventilation where intake and exhaust occur at different ends of the attic depending on wind direction. When one mixes gable end louvers with ridge vents, however, the venting system is short circuited when air enters through the gable end louver and exits through the ridge vent in close proximity to the gable wall with the louver in it. Thus, the air at the lower portions of the attic and in the middle of the attic midway between the gable end louvers becomes stagnant and may result in a build up of excessive heat or moisture.

NOTE: Although this interpretation is based on the requirements of the IBC it is likewise applicable to attic ventilation in building construction governed by the 2003 International Residential Code portion of the 2005 State Building Code.

**Ed the Roofer** · 09-08-2007, 05:57 PM

This is regarding Pigs and ventilation, but concludes the same thing about short-circuiting the attic ventilation.

Ed

VENTILATION BASICS FOR SWINE

Mark Storlie, ISU Extension Swine Field Specialist, August, 2006
Reviewed by Jay Harmon, ISU Ag Engineer; Steve Hoff, ISU Ag Engineer and Dan Meyer, ISU Extension Ag Engineer
Over the years, several people have requested information or specific suggestions on the temperature they should
maintain their building for a certain pig weight or age. My general response “let the pigs tell you.” The fact is that
there is not a specific temperature that is appropriate for all building designs. The intent of this paper is to give a
brief overview of ventilation factors and principles that may help you establish the appropriate effective
environment for pigs in your operation or specifically your buildings. Different set points may be appropriate for
different building type, ventilation system, and season changes within the same operation.
Energy Exchange – four basic methods:
Conduction – transfer of heat by physical contact with another surface. Ex: floor, walls, etc.
Convection

– transfer of heat by physical contact with air, mud or water. Ex: Cold daft – negative, but positive when cooling.

Radiation

– heat transfer as result of “radiatively seeing” surface temps that differs from the pigs surface. Ex: Stand next to

a large window, in winter it is feels colder, while in summer feels warmer than the air temp of the room.
Evaporation

– heat transfer as result of water conversion to a vapor. Ex: Breathing – water evaporation in respiratory tract and

useful in cooling systems such as sprinklers and drippers.
Assessing the Thermal Environment:
Air Temperature – thermometers; affects convection, and evaporation
Speed of Air Moving over the pigs

– smoke (stick, bag,etc.), digital, paddlewheel sensors; affects convection and evaporation

Surface Temperatures

– infrared thermometer; affects conduction and radiation

Relative Humidity –

hygrometer; affects convection and evaporation

Add them up = EFFECTIVE ENVIRONMENTAL TEMPERATURE (EET)

Be critical of potential drafts from air inlets, door ways and in winter, unused summer fans leaking. Ensure that enough air

inlet area is provided – too few inlets or too many shut off will increase the speed of air entering and may cause drafts.
Leaving a door open in summer will “short-circuit” the system and actually increase effective temperature by reducing airspeed.
Observe influence of lights, feed and water line on air current if placed in front of inlet air. Ensure enough attic intake
area is provided – protective covering with 3/8” holes. House soffit covering is too restrictive and can plug easily with dust
or snow, thus increase the static pressure in the building.

**Ed the Roofer** · 09-08-2007, 06:04 PM

And, here is a good thread from another forum about actual hands on experiences from home inspectors.

Ed

http://www.nachi.org/forum/showthread.php?t=10736

dennis · 09-08-2007, 09:50 PM

Hi Ed, and thanks for the links. I did read through them.

From your first link;

"ABSTRACT

This report was commissioned by the New York State Energy Research and Development
Authority and the New York State Department of State to review the history and state-ofthe-
art of attic ventilation and air sealing. It includes a mathematical model that is used to
examine the complex relationships between such variables as attic bypass leakage area,
outside air temperature, household moisture production, and venting area. The primary
recommendation is to reduce heat and moisture flows into the attic by permanently sealing
all air leakage paths between the house and attic, especially in climate areas that experience
sustained periods of low wintertime temperatures. It concludes that current attic ventilation

codes, which omit reference to considerations of climate zones, are of marginal utility to the
building or retrofit industry and are in need of revision. Recommendations for further
research are included."

"Nonetheless, building codes, HUD standards, and ASHRAE "past practice"
recommendations have led to relatively uniform attic ventilation standards. These
standards usually require attics to have one square foot of net free vent area for every
300 square feet of insulated ceiling area. In many areas, twice as much ventilation
(a ratio of 1 in 150) is required in buildings with flat roofs and cathedral ceilings or if
there is no vapor barrier. These standards were developed in the 1940s based on
limited field experiments. "

"The primary research on ventilation air flows was performed in 1962 by a research
engineer for a company that manufactures attic vents (Hinrichs, 1962)."(not particularly unbiased, I am still looking for a copy of this paper)

" In reality, there is no guarantee that providing a specified area of passive ventilation openings will yield some desired level of ventilation. Predicting ventilation flow rates is difficult due to difficulties in modeling site-specific wind patterns, especially at shielded sites, and the
unpredictable effects of wind speed and direction on a given system of vents. "

" The American Society of Heating, Refrigeration, and Air
Conditioning Engineers (ASHRAE), a major building science organization, altered its
description of venting standards from"Recommended Good Practice" to "Past
Practice" in 1981, and has made no new recommendations since then. "

I will stop there.

Your second link/report is from 1985. Nothing new there, although I like the illustrations, (they are about as sophisticated as mine)lol.

The IBC codes are based on the same old studies reffered to in the above paper and on manufacturers installation instructions.

Not sure what to make of the swine barn referance.
"Leaving a door open in summer will “short-circuit” the system and actually increase effective temperature by reducing airspeed."
Wouldn't that be the same as opening a soffit vent???

I am still looking for a recent scientific study that uses computational fluid dynamics for it's modeling of wind and airflow around buildings and in attics.

And I have seen many referances to the "short circuit" of ventilation systems. But I have never seen any scientific study that illustrates or tests the idea.

I have seen a study that shows that airflow through an attic is not laminar, but turbulent. Which adds another variable to the equation. I'll see if I can find and post it.

I do appreciate your time and effort. I'm not trying to be bullheaded. Just trying to figure it out.

**Ed the Roofer** · 09-08-2007, 10:38 PM

Good for you and me too Dennis.

I am always looking for alternative explanations.

By the way, here are the key search words to try to locate that document you desired to locate. I don't have any more time tonight to search for it, but I have already found it referenced to in several other papers.

Hinrichs, H,S, "Comparative Study of the Effectiveness of Fixed Ventilating

Louvers," Ac_J:iEL/_.TransactionVso,l, 68, pp.297-309, ASHRAE, Atlanta, GA,1962.

I noticed you did not make a comment regarding the thread from the NACHI forum, which depicted many inspectors real life observations from a short circuited ventilation system. I am sure you will get to reading through that thread in due time though.

There is another guy on that forum who challenges the neccessity of attic ventilation at all. He is from Canada, but the links he threw at me were very well thought out and full of supporting observations and testings. I disagree with him on the lack of a need for attic ventilation, but I applaud his conviction and resourcefullness of plucking out so many technical documents and scientific laboratory controlled simulations to support his stance.

I will edit and post a link to that attic ventilation thread for you. There is a chit-load of links contained within its contents.

Here is that link:

http://www.nachi.org/forum/showthread.php?t=19078

Go there and post something to bring it back up to the top. It warrants a bump, but not from me.
Ed

**Ed the Roofer** · 09-08-2007, 10:51 PM

Here is another great document, which is lengthy, but very informative.

http://www.fsec.ucf.edu/en/publicati...CR-1526-05.pdf

Ed

reveivl · 09-09-2007, 01:40 AM

"however, the venting system is short circuited when air enters through the gable end louver and exits through the ridge vent in close proximity to the gable wall with the louver in it. Thus, the air at the lower portions of the attic and in the middle of the attic midway between the gable end louvers becomes stagnant and may result in a build up of excessive heat or moisture."

Now this comment requires some thought (beyond the inappropriate use of an electrical metaphor for air movement driven by heat).

"may result in a build up of excessive heat or moisture" It seems to me that if heat is building up in "the air at the lower portions of the attic and in the middle of the attic" then according to all physics and all experience, this air will rise and not remain stagnant. It will take any moisture with it and leave via the ridge vent or the gable vents.

Hang onto this thought: Hot air rises.

08-31-2007, 12:27 PM	#1
tacoma5050 View Profile tacoma5050 Registered User Send Message Follow Blogs (0) Threads (2) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Registered User Trade: Gen Construction Join Date: Aug 2007 Posts: 2	Seal Gable Vents After Ridge Vent Installed? I just replaced a roof with 30yr asphalt fiberglass shingles. Previously there were only gable vents and the customer wanted a ridge vent so I installed one. There are only three small soffit vents, so I will be adding soffit vents at each rafter spacing. Someone suggested that once there is proper soffit ventilation and a ridge vent, that I should seal off the gable vents. The therory being that the gable vents will disturb or decrease the disired air flow from the soffit vent to the ridge vent, or that the ridge vent will pull more air from the gable vent then from the soffit vent. I would assume that we want the gable vent to pull most air from the soffit vent and not the gable vent. Any comments? Thanks.... The house is a 2 story colonial in the northeast with a walkable pitch.

08-31-2007, 01:01 PM	#2
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? [quote=tacoma5050;282597] I would assume that we want the gable vent to pull most air from the soffit vent and not the gable vent. quote] I presume that you meant to say Ridge Vent to pull most air from the soffit vent and not the gble vent. Please download the free ventilation publication from Air Vent Corporation, entitled "The Principle Of Attic Ventilation", which will be a constant source of information for you, and you can even order the printed booklette for free. Yes, according to proper air flowage dynamics, the gable vents should be sealed off so as to not "Short-Circuit" the attic ventilation flowage. Ed

08-31-2007, 07:42 PM	#4
Tom R View Profile Tom R Pro Send Message Follow Blogs (0) Threads (6,484) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Carpenter Join Date: May 2004 Posts: 6,484	Re: Seal Gable Vents After Ridge Vent Installed? One time I did an addition on the back of a rancher, - - the main house had gable end-vents, - - but my addition had soffit and ridge vents. I reverse-gabled the (fairly low-pitched) addition onto the existing roof. I installed cobra ridge vent and shingled the roof. And at some point I cut a hole through the existing (now covered part of the) roof for attic-access from old to new. Anyway, - - that night it snows and when I show up in the morning, - - there was a straight line of actual snow on the subfloor directly below the ridge vent Turned out I finally figured out the gable vents combining with the ridge vents were creating a reverse air-flow and actually drawing the snow 'into' the building. I installed a (removable) cover over the access-hole, - - and no more leaks ever again . . .

08-31-2007, 08:38 PM	#5
PlainPainter View Profile PlainPainter Pro Send Message Follow Blogs (0) Threads (431) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Join Date: Dec 2004 Posts: 431	Re: Seal Gable Vents After Ridge Vent Installed? This begs the question - if a building has already gable vents - is there a real need for ridge vents? Perhaps this is before the practice of insulating an attic - where as now if an attic is insulated, you still want a flow of air between the insulation and roof decking. And if the attic is insulated - if you cut off the gable vents - the space is no longer ventilated - so it might be you want both in those circumstances.

08-31-2007, 10:43 PM	#6
dennis View Profile dennis Pro Send Message Follow Blogs (0) Threads (158) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Join Date: Nov 2004 Posts: 158	Re: Seal Gable Vents After Ridge Vent Installed? I will have to respectfully disagree with ed's reply. Unless your house looks exactly like, and the air flow dynamics are the same, as the one on the airvent site. I think there are too many variables for a simple solution. My reasoning is explained here http://roofersreview.com/Ventilation and here http://roofersreview.com/htmlpage2

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09-04-2007, 09:51 PM	#9
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? Thanks for the links Dennis. I will copy them and read through the information later this week when I have more time. I do have a particular insight into some additional air dynamics testing results from an intake ventilation manufacturer which surprised him about the water flowing upwards under the shingles, but I am awaiting the hard copy of the reports from an independant testing laboratory first, so I can draw my own conclusions. I was involved very deeply in another forum with many pros and cons being brought forth which each had their own merits. Sometimes, you can only decipher all of the scientific mumbo-jumbo so much, and then go to work doing what is commonly accepted. Ed Last edited by Ed the Roofer; 01-19-2008 at 06:06 PM.

09-06-2007, 01:08 AM	#10
theroofinggod View Profile theroofinggod Expert Roofer Send Message Follow Blogs (0) Threads (322) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Expert Roofer Trade: ROOFING/HOME IMPROVEMENTS-WINDOWS/SIDING/GUTTERING/COPPER WORK,ETC Join Date: Jun 2007 Location: pomona,new york,10970 Posts: 322	Re: Seal Gable Vents After Ridge Vent Installed? "on the road again"eh dennis--you are untiring in this pursuit,my info agrees w/ ed,Tom r apparently didn`t nail the ridge vent down well before capping it,1st time I`ve heard of that

09-06-2007, 07:35 PM	#11
dennis View Profile dennis Pro Send Message Follow Blogs (0) Threads (158) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Join Date: Nov 2004 Posts: 158	Re: Seal Gable Vents After Ridge Vent Installed? theroofinggod. I would be happy to look at "your info". Can you direct me to the scientific information that supports your ideas?

09-07-2007, 01:26 AM	#12
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? Dennis, Read page 17 of the following link regarding gable vents. http://www.osti.gov/energycitations/...e/10186298.pdf The following descriptions of passive venting strategies are based more on anecdotal evidence and a consensus of practitioners than on actual measurements (see Forgues, 1985 for a more detailed discussion of attic venting strategies): " Gable vents": Usually consisting of a set of horizontal louvers shaped to discourage the entrance of precipitation, are installed on vertical surfaces in the attic. They can provide high flow rates but depend strongly on wind direction. They are inexpensive and are often the only existing ventilation, however they do not usually provide good air flow at lower portions of the attic unless combined with soffit vents. They do not get covered with snow but may allow entry of wind driven snow in some circumstances if not properly re-designed when installed (some contractors fasten a thin layer of fiberglass over the opening and fabricate a drip tray with flashing in order to avoid snow entry). Contractors report commonly finding plastic over gable vents installed by homeowners to solve this problem.The large air flows through gable vents have also been reported to create suction at roof louvers and thus draw snow into the attic. Ed Last edited by Ed the Roofer; 09-07-2007 at 01:29 AM.

09-08-2007, 05:39 PM	#13
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? Dennis, I thought you might find this older paper useful too. http://irc.nrc-cnrc.gc.ca/pubs/bpn/57_e.pdf Ed

09-08-2007, 05:45 PM	#14
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? Here is another paper stating proper requirements. This is the link for this paper: http://ct.gov/dps/lib/dps/office_of_...07/i-11-07.pdf Ed STATE BUILDING CODE INTERPRETATION I-11-07 April 9, 2007 The following is offered in response to your request for an interpretation of the provisions of Section 1503.5 of the 2003 International Building Code (IBC) portion of the 2005 State Building Code. Question: When re-roofing a building that has existing gable end louvers for attic ventilation, can one add ridge vents without adding soffit vents and disabling the gable end louvers? Answer: No. Section 1503.5 of the IBC states, in part, that roof intake and exhaust vents shall be installed in accordance with the manufacturer’s installation instructions. A review of a variety of manufacturer’s installation instructions as well as several ICC evaluation reports for ridge vents indicates that in all cases reviewed the ridge vents are intended to be installed in conjunction with eave, cornice or soffit vents. The combination of low intake vents at the eave, cornice or soffit, and high exhaust vents at the ridge promotes uniform ventilation of the entire attic space based on cooler air entering at the low vents and warmer air exhausting at the high vents. Gable end louvers, while not as efficient as a combination low and high system, likewise promote uniform ventilation where intake and exhaust occur at different ends of the attic depending on wind direction. When one mixes gable end louvers with ridge vents, however, the venting system is short circuited when air enters through the gable end louver and exits through the ridge vent in close proximity to the gable wall with the louver in it. Thus, the air at the lower portions of the attic and in the middle of the attic midway between the gable end louvers becomes stagnant and may result in a build up of excessive heat or moisture. NOTE: Although this interpretation is based on the requirements of the IBC it is likewise applicable to attic ventilation in building construction governed by the 2003 International Residential Code portion of the 2005 State Building Code. Last edited by Ed the Roofer; 09-08-2007 at 08:56 PM.

09-08-2007, 05:57 PM	#15
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? This is regarding Pigs and ventilation, but concludes the same thing about short-circuiting the attic ventilation. Ed VENTILATION BASICS FOR SWINE *Mark Storlie, ISU Extension Swine Field Specialist, August, 2006* Reviewed by Jay Harmon, ISU Ag Engineer; Steve Hoff, ISU Ag Engineer and Dan Meyer, ISU Extension Ag Engineer Over the years, several people have requested information or specific suggestions on the temperature they should maintain their building for a certain pig weight or age. My general response “let the pigs tell you.” The fact is that there is not a specific temperature that is appropriate for all building designs. The intent of this paper is to give a brief overview of ventilation factors and principles that may help you establish the appropriate effective environment for pigs in your operation or specifically your buildings. Different set points may be appropriate for different building type, ventilation system, and season changes within the same operation. Energy Exchange – four basic methods: Conduction – transfer of heat by physical contact with another surface. Ex: floor, walls, etc. Convection – transfer of heat by physical contact with air, mud or water. Ex: Cold daft – negative, but positive when cooling. Radiation – heat transfer as result of “radiatively seeing” surface temps that differs from the pigs surface. Ex: Stand next to a large window, in winter it is feels colder, while in summer feels warmer than the air temp of the room. Evaporation – heat transfer as result of water conversion to a vapor. Ex: Breathing – water evaporation in respiratory tract and useful in cooling systems such as sprinklers and drippers. Assessing the Thermal Environment: Air Temperature – thermometers; affects convection, and evaporation Speed of Air Moving over the pigs – smoke (stick, bag,etc.), digital, paddlewheel sensors; affects convection and evaporation Surface Temperatures – infrared thermometer; affects conduction and radiation Relative Humidity – hygrometer; affects convection and evaporation Add them up = EFFECTIVE ENVIRONMENTAL TEMPERATURE (EET) Be critical of potential drafts from air inlets, door ways and in winter, unused summer fans leaking. Ensure that enough air inlet area is provided – too few inlets or too many shut off will increase the speed of air entering and may cause drafts. Leaving a door open in summer will “short-circuit” the system and actually increase effective temperature by reducing airspeed. Observe influence of lights, feed and water line on air current if placed in front of inlet air. Ensure enough attic intake area is provided – protective covering with 3/8” holes. *House soffit covering is too restrictive* and can plug easily with dust or snow, thus increase the static pressure in the building. Last edited by Ed the Roofer; 09-08-2007 at 06:06 PM.

09-08-2007, 06:04 PM	#16
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? And, here is a good thread from another forum about actual hands on experiences from home inspectors. Ed http://www.nachi.org/forum/showthread.php?t=10736

09-08-2007, 09:50 PM	#17
dennis View Profile dennis Pro Send Message Follow Blogs (0) Threads (158) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Join Date: Nov 2004 Posts: 158	Re: Seal Gable Vents After Ridge Vent Installed? Hi Ed, and thanks for the links. I did read through them. From your first link; "ABSTRACT This report was commissioned by the New York State Energy Research and Development Authority and the New York State Department of State to review the history and state-ofthe- art of attic ventilation and air sealing. It includes a mathematical model that is used to examine the complex relationships between such variables as attic bypass leakage area, outside air temperature, household moisture production, and venting area. The primary recommendation is to reduce heat and moisture flows into the attic by permanently sealing all air leakage paths between the house and attic, especially in climate areas that experience sustained periods of low wintertime temperatures. It concludes that current attic ventilation codes, which omit reference to considerations of climate zones, are of marginal utility to the building or retrofit industry and are in need of revision. Recommendations for further research are included." "Nonetheless, building codes, HUD standards, and ASHRAE "past practice" recommendations have led to relatively uniform attic ventilation standards. These standards usually require attics to have one square foot of net free vent area for every 300 square feet of insulated ceiling area. In many areas, twice as much ventilation (a ratio of 1 in 150) is required in buildings with flat roofs and cathedral ceilings or if there is no vapor barrier. These standards were developed in the 1940s based on limited field experiments. " "The primary research on ventilation air flows was performed in 1962 by a research engineer for a company that manufactures attic vents (Hinrichs, 1962)."(not particularly unbiased, I am still looking for a copy of this paper) " In reality, there is no guarantee that providing a specified area of passive ventilation openings will yield some desired level of ventilation. Predicting ventilation flow rates is difficult due to difficulties in modeling site-specific wind patterns, especially at shielded sites, and the unpredictable effects of wind speed and direction on a given system of vents. " " The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE), a major building science organization, altered its description of venting standards from"Recommended Good Practice" to "Past Practice" in 1981, and has made no new recommendations since then. " I will stop there. Your second link/report is from 1985. Nothing new there, although I like the illustrations, (they are about as sophisticated as mine)lol. The IBC codes are based on the same old studies reffered to in the above paper and on manufacturers installation instructions. Not sure what to make of the swine barn referance. "Leaving a door open in summer will “short-circuit” the system and actually increase effective temperature by reducing airspeed." Wouldn't that be the same as opening a soffit vent??? I am still looking for a recent scientific study that uses computational fluid dynamics for it's modeling of wind and airflow around buildings and in attics. And I have seen many referances to the "short circuit" of ventilation systems. But I have never seen any scientific study that illustrates or tests the idea. I have seen a study that shows that airflow through an attic is not laminar, but turbulent. Which adds another variable to the equation. I'll see if I can find and post it. I do appreciate your time and effort. I'm not trying to be bullheaded. Just trying to figure it out.

09-08-2007, 10:38 PM	#18
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? Good for you and me too Dennis. I am always looking for alternative explanations. By the way, here are the key search words to try to locate that document you desired to locate. I don't have any more time tonight to search for it, but I have already found it referenced to in several other papers. Hinrichs, H,S, "Comparative Study of the Effectiveness of Fixed Ventilating Louvers," Ac_J:iEL/_.TransactionVso,l, 68, pp.297-309, ASHRAE, Atlanta, GA,1962. I noticed you did not make a comment regarding the thread from the NACHI forum, which depicted many inspectors real life observations from a short circuited ventilation system. I am sure you will get to reading through that thread in due time though. There is another guy on that forum who challenges the neccessity of attic ventilation at all. He is from Canada, but the links he threw at me were very well thought out and full of supporting observations and testings. I disagree with him on the lack of a need for attic ventilation, but I applaud his conviction and resourcefullness of plucking out so many technical documents and scientific laboratory controlled simulations to support his stance. I will edit and post a link to that attic ventilation thread for you. There is a chit-load of links contained within its contents. Here is that link: http://www.nachi.org/forum/showthread.php?t=19078 Go there and post something to bring it back up to the top. It warrants a bump, but not from me. Ed Last edited by Ed the Roofer; 09-08-2007 at 10:57 PM.

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09-08-2007, 10:51 PM	#19
Ed the Roofer View Profile Ed the Roofer Pro Send Message Follow Blogs (0) Threads (7,135) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Roofing Contractor Join Date: Dec 2006 Location: NW Suburbs of Chicago Posts: 7,135	Re: Seal Gable Vents After Ridge Vent Installed? Here is another great document, which is lengthy, but very informative. http://www.fsec.ucf.edu/en/publicati...CR-1526-05.pdf Ed

09-09-2007, 01:40 AM	#20
reveivl View Profile reveivl Pro Send Message Follow Blogs (0) Threads (1,716) Photos (0) Reviews (0) Projects (0) Toolbox (0) View All Activity Pro Trade: Renovations Join Date: May 2005 Location: West Coast Canada Posts: 1,716	Re: Seal Gable Vents After Ridge Vent Installed? "however, the venting system is short circuited when air enters through the gable end louver and exits through the ridge vent in close proximity to the gable wall with the louver in it. Thus, the air at the lower portions of the attic and in the middle of the attic midway between the gable end louvers becomes stagnant and may result in a build up of excessive heat or moisture." Now this comment requires some thought (beyond the inappropriate use of an electrical metaphor for air movement driven by heat). "may result in a build up of excessive heat or moisture" It seems to me that if heat is building up in "the air at the lower portions of the attic and in the middle of the attic" then according to all physics and all experience, this air will rise and not remain stagnant. It will take any moisture with it and leave via the ridge vent or the gable vents. Hang onto this thought: Hot air rises. __________________ From where does knowledge come? If you need to know what is in a box, you could ask someone (not reliable), you could pray, (not useful), you can consult with the scripture (not helpful) or you could open the box (science)