*
I have a house at the beach and I am concerned about proper attic
ventillation. Presently, there are three gable vents, a continuous soffit vent,
a powered attic fan, and two 10″ by 10″ vents that appear to be abandoned–one
was damaged in a hail storm and admits water into the attic. The last two vents
I would like to remove. I am also getting water infiltration through the gable
vents. These are just some off-the-shelf wood gable vents with no special
severe-weathering characteristics. These too I would like to remove. I want to
install a continuous ridge vent in their place because I am convinced I will get
superior ventillation. Is this correct? Also, what type of ridge vent do you
reccommend for installation at the beach. Lastly, If I decide to leave the gable
vents, are there better performing gable vents than what I have. The house has
fiberglass shingles and hardiplank siding.
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Replies
*
John,
The best venting combination is continuous soffit
vents coupled with a ridge vent. The problem is that,
due to house configuration, you may be undersized.
The rule of thumb is to use 1 sq. ft. of vent for 150
to 300 sq. ft. of attic floor. How "severe" is your
weather condition. You never said where this house
is. I would always go for 1 sq. ft. to 150 or 200 sq.
ft. as a rule (for most harsh climate areas of the
country).
Thing is, this may require the addition (or re-use)
of gable end vents. They are great and powerful ways
of increasing ventilation. I don't know where to go
to get well profiled vanes in these vents. They
should have some sort of minimal drip edge built into
them and a decent overlap to boot. Try calling some
local storm window manufacturers.
*John,What are you trying to achieve with the ventilation? Is this a summer-only house? Are you trying to keep the house cool? Are you trying to keep the attic dry? Is this a year-round residence? Do you heat the house in winter? Is it insulated? With what? What is the climate like?The answers to these questions will help determine if you need more venting or less or none, and may point the way to better solutions for your particular problems.Steve
*John. FredL's points are well taken. What do you mean by "proper attic ventialtion"and what do you think it will do for you? By the bye. It is just about impossible to design a gable-end luvered vent that will not take in rain or snow. GeneL.
*Something I've never done, but have thought of is to put in a gable end vent and set it on a very wide piece of flashing; 18" or so, turn this upward inside the attic and brace it with some pieces of wood tied at a angle to the studs. This way any splatters of rain that gets in will drain out to the exterior. Even though, I've never really heard of them causing that much trouble in an attic. They could reak havoc on cellulose insulation, but that's about all.gg
*Garyg. The best solution to gable-end louvered ventsisis to not install or use them. Because they are wind dependent they work only when the wind blows directly into them--wind parallel to ridge. When the wind is perpendicular to the ridge only a tiny amount of air enters the vent. The entering air moves in a short distance then turns around and exits the same entrance vent. See chapter 23 Attic Ventilation in my book, _Complete_Building_Construction_4th Edition, published by Macmillan.The chapter shows all the air flow paths for the various attic ventilation devices.No, adding soffit vents makes no difference. GeneL.
*Gene,Gotta question this one. IF you have a ridge vent then I contend you will have thermosiphoning air flow of hot air out. No doubt about it, hot air will rise. This creates suction. Suction draws in air from all other available openings. This would include soffit and gabel end vents. If anything, the gable end vents might short circuit air flow from soffit vents (IF they all existed in the same building), since they are closer to the ridge.Any comments?gg
*Garyg. ONLY :-}If you have the right combination of ridge/soffit vents will you have thermosiphoning.By the bye. The suction takes place without soffit vents or warm air rising. The external baffle causes the wind to jump over the vent and the result is suction.Excessive soffit NFVA-Net Free Venting Area-will short circuit the ridge vent. Little or none of the soffit air flow reaches the ridge vent. You are correct about the gable-end louvered vents short-circuiting the ridge vents--path of least resistance.GeneL Ridge vents without an external--internal baffles are No-NOS-- bring in air rather than exhausting it. This is true even if the soffit vents are correct. Use only a continuous double louvered soffit vent--single-louvered soffit vents can be installed two ways, one of which is wrong--located next to the fascia board. DO NOT use drip-edge vents. GeneL.
*And for Gabe's snidely pleasure...sign me...ventlessly near the stream,j
*I'm renovating an additon on the north side of my house (see "Addition Renovation" thread). As I've been planning I've read a lot of books, websites, manuals, etc., and Fred's postings here on insualtion & ventilation are the first I've ever heard of not venting an attic. My question is regarding baffles: Are there any opinions on the qualitative differences between plastic and styrofoam baffles? Also, since the addition's angled roof meets the exterior wall a ridge vent is out. I haven't been able to locate a "roof to wall" vent although I've seen them referred to in the literature. Suggestions? Brent
*garyg. I'm in agreement with Fred. But, as I noted these last several years, many are afraid of not venting.I argue that if you must vent (the vent police say you MUST, evberyboidy says ridge/soffit vents is the way ands son on) then do it right even if that right isn't quite right.But attic vents are asked to do things they were never designed to do. The FIRST:-} line of defense against ice dams and moisture problems is not attic ventilation. It begins in the basement by sealing all the openings in the cellar ceiling, and doing the same thing in the attic by sealing all the openings in the attic floor.Brent. The vent you are looking for is a flash vent and is manufactured by Air vent, Inc. WARNING.The junction of the roof and exterior wall is in the high wind pressure zone.Putting a vent there guarantess rain and snow penetration.Seal the ceiling by eliminating all penetrations. No penetrations means no moisture laden air getting in the ceiling. Beef up the insulation levels with blown-in cellulose. Do not use fiberglass.Retarding, minimising--you can't stop it-both the moisture movement and heat movement into the attic, reduces if not eliminates the need for ventilation. GeneL.
*If possible a good way to vent this shed roof condition is to vent the roof up through the exterior walls it leans against, into the attic and out. This would require opening up the walls and inserting those syrofoam baffles or dams that are sold for rafter cavities. You could also use circular mushroom roof vents on the roof, below the junction of roof to wall.To all those people out there who are skeptical about the need for venting, wake up! Moisture is produced in great quantities within a house; bathrooms, people emit it, kitchens, laundry, drying firewood inside the house, etc.. This moisture will condense as soon as it hits a cold surface. Even great vapor barriers do not create perfect non-permeable, zero emissivity envelopes. This moisture condenses and hurts your cellulose, or rots your wood studs, or sogs your fiberglass and hurts it's R-value, and probably does other nasty stuff too. So, ventilate that old attic boys !!! and don't look back!gg
*>>Moisture is produced in great quantities within a house... This moisture will condense as soon as it hits a cold surface.<<In agreement here, Gary, but then is it really wise to suggest that we channel this moist air up through the cold shed-roof rafters, through the cold exterior wall framing and on into the cold attic, where it will it will, as you so aptly put it, "condense, hurt your cellulose, or rot your wood studs, or sog your fiberglass and hurt it's R-value, and probably do other nasty stuff too?Wouldn't it be wiser to try and keep it out of the framing in the first place, by creating a sound air barrier and evacuating the air via more controllable, less damaging routes, like vent fans or heat exchangers?I can understand the argument for venting in the event that moisture does make it's way into the cold spaces. Doing it in a fashion that lets the attic ventilate without causing damage from rain and snow penetration is the trick. Advocating chanelling the moisture through the cold spaces intentionally seems couterproductive.Steve
*With a ceiling properly sealed, would soffit vents alone be enough to prevent moisture build up from what little moisture gets into the attic from the few imperfections that still are there in the ceiling?
*The exterior wall the roof connects to is two layers of brick so I don't think its feasable to go up through that wall. Any thoughts on plastic vs. styrofoam baffles? Attached is a picture of the shedexterior showing the open cornice(before everyone asks about that gutter, I moved it to try to show more for the pic). I could build a soffit, but what of the probability of venting directly throught thewall? Would this pose the same problem as a gable vent & let in snow, rain, etc? The exposure is north. Thanks.
*Thanks Fred,I am kind of thinking about the old 10 to 1 permiability rule of vapor barriers. If the ceiling has 1 square foot of net effective leakage then put in 10 square feet of vent but put it where water won't get blown in. (And use cells to keep radiant summer heat out of the house.)Ron
*Ron. On the positive side soffit vents provide air flow regardles of wind direction. But the negatives are greater: (1) With the wind perpendicular to the ridge the air flow is from the soffit on one side to the side opposive. But when the wind is parallel to the ridge the air enters one end of the soffit vent, moves into the attic in a semi circular path and exists out the other end of the same soffit; (2) the air flow is confined to the attic floor where it could reduce the attic floor insulation effectiveness; (3)the underside of the roof sheathing is not ventilated and little moisture is removed; (4)what little effectiveness they have is due to the wind; (5) there is no air movement due to thermal effect, when there is no wind; (6) they MUST :-} be located next to the fascia board. GeneL
*GaryR. Steve is right on. As I said earlier stay away from trying to ventilate a shed roof attached to a vertical wall. It is in ahigh pressure area and snow and rain penetration are guaranteed. Although such a vent--flash vent--is made for that purpose, the manufacturer's reps report trouble with this attempt to ventilate. Part of the reason being builders rarely install it correctly.GeneL.
*Hi Y'all. I have a 1902 victorian in Central Illinois. I have done a LOT of reading about the whole ventilation issue but have not found a definitive answer so I came up with my own solution. I basically tried to hedge my bets.I read all about the ridge and soffit vents and it certainly made more sense than the power vent that was installed in the 70s. I have used Icynene in the walls and read the literature claiming you didnt need a roof vent if you used Icynene.So, I installed the ridge vent on my 12/12 roof when I stripped, decked and shingled. I put in the soffit vents by notching the lookouts right behind the facia and nailing right behind the facia. An unobtrusive look.The attic is floored with 12 foot ridge. I put 1-by spacers under the spaced decking from the cedar roofing. To this I attached 1/4 plywood between the rafters to provide a channel for the air. I painted the side of the plywood facing the roof just in case. Now, when I finish this I plan to have the Icynene sprayed between the rafters onto the panels I installed. My thinking is that I should have a complete, or very near complete, seal with the Icynene and have a good channel for airflow.I just wonder what you might think about this? Im keeping it regardless, just curious about other opinions. By the way, no need for flames, but sincere thoughts pro or con are appreciated.
*I am new to this discussion group, and I hope you can help me. I am in the process of building a new house in Pine Mountain, GA. We will have continuous ridge vents and soffitt vents for ventilation. We will also have windows in the garage that can be opened.I would like to put a whole house fan in the garage to use 90 - 95 degree air from the outside to force out the superheated air in the attic, when the house is being air conditioned. I called Ga Power Goodcents and the engineer there said that if I had R30 insulation in the attic, adding the fan would not do any good. He didn't think it would do any harm, either.What do you think? Is it worth $400-$500 to install this fan? Will it do any good? Can it do any harm?Thanks for your help, MikeM
*MikeM. Keep in mind that the main heat transfer mechanism in an atic is radiation. Radiation cannot be flushed out of an attic by ventilating it. Not all combinations of ridge/soffit vents work. The only ridge vent that works is one with an exterior baffle. The soffit vents must be continuous double-louvered vents located next to the fascia board.If the house and garage are under the same roof, if the garage ceiling is open,and if the garage doors, winmdows or both are open, the ridge vent will reverse: air will be sucked into the garage and attic. The air change per hour (ACH) in an attic with an airight ceiling ,no ductwork and vented to code, is 3 to 6 air changes per hour. At this rate the heat transfer to the rooms below will be reduced 2 to 3 percent.If leaky ductwork is installedin the attic space the heat transfer to the rooms below--the conditioned spaxe- is increased by 25%. In the South air conditioning ductwork is usually located in the attic.Years of testing the effects of power venting attics shows that even if the attic temperature is reduced by 20 to 30 degrees, it has little or no effect on the house's total air conditioning load. All researchers agree that insulation is the most effective and least costly way to retard, slow down the heat transfer from the attic to the conditioned space below.What happens if one ventilates one's attic in Georgia Or anywhere in the USA where the summers are hot, humid or both? Bringing hot humid air into an attic full of air conditioning ductwork spells disaster. The first thing the hot humid air (HHA) sees is cold R-6 insulated ductwork,where it readily condenses, and drips, drips. Another thing the HHA sees is the ceiling without a vapor diffusion retarder (VDR). Interior VDRs are a No-no in the south. The HHA diffuses through the insulation until it reaches the cold, air conditioned ceiling. It condesnses and guess what? Building scientists including those at the Florida Solar Energy Center are arguing for insulation not ventilation. Beef up the attic insulation, preferably with cellulose, and forget the ventilation. GeneL.
*b ATTIC HEAT:I am reinsulating an older home in southern Wisconsin. I plan on using the attic for some storage and want to know how to prevent abominable summer temperatures in the storage space. I was considering a solar powered ventilation fan. I am confused by the information here which continually pooh-poohs ventilation of attics but does not seem to be addressing the issue of high summertime temperatures. Any help?
*Mike,What kind of insulation do you have? If it is fiberglass the fan would help a little. If it is cellulose, its radiant heat blocking ability is so good that the fan would do no help. It it is fiberglass, a few inces of cellulose over the fiberglass will work better than the fan, use no electricity and cost less to install.
*Hi Johnnie,If you want the attic itself to stay cool, you'll have to insulate the rafter bays themselves, not the attic floor, and use an insulation that is effective at stopping radiant heat transfer, which Fiberglass does not do well. Cellulose is good for this, what else, I'm not sure of. Others like foil radiant barriers, but they must be installed in specific ways and kept free of dust build-up (yeah right, in an attic?).See Gene's post (#17 in this thread) about attic fans. I'm not sure if he means a fan will only be able to lower the attic temp 20-30 degrees. Maybe he will clarify. How cool do you want it to be in your attic?Steve
*Gene, You have stated countless times that the only kind of ridge vent that works, is one with an exterior baffle. In 30 years of installing thousands of roofs in NE Ohio, a location that gets hot and cold weather extremes, the only problems I have encountered with ridge vents, are the aluminum and plastic ridge vents eventually leaking at the seams(plus the fact they are ugly).When concealed ridge vents became available, I started using them exclusively.(Ridge-line and Core vent are the brands I use). They look good, because you can't see them- there are no baffles, and THEY DON"T LEAK!It's not just me, other roofers I talk to don't have problems with these ridge vents. You write as though it is accepted fact that baffled ridge vents are the only ones that work. I can tell you that is simply not true.Truly baffled, John
*So we have two simultaneous meanings of a ridge vent "working": (1) leaking air; and (2) not leaking water.Ah, this clarifies things for me too.
*JRS. I first used a ridge vent--manufactured by Air Vent, Inc., on the 1977 Leger House. Although it was aluminum, easily damaged-we were careful with the installation. Twenty-two years later it still works and has never leaked. Air Vent's externally baffled ridge vent is the only ridge vent I have used for the last 22 years.We never had a leaky ridge vent. If a ridge vent leaks it's because it is incorrectly installed, or it is taking in water, or snow.I intend no offense when I say that builders are fond of saying "We've had no problems." By the time the problem appears the warranty has expired or the builder is long gone. But dwellers in the snow belt are treated annualy to the millions of dollars of ice dam damage.If all these attic ventilation devices are working how account for the staggering cost and the severity of the damage from ice dams? Over the last several years here in New England we have had some beautiful ice dam winters.Ice dams were found on houses with unvented attics, attics vented according to code, on metal roofs. Imagine the shock to the home owner when his heat tape equipped roof had ice above, below, over, under the heat tapes. Yes, and many houses with ridge/soffit vents had ice dams. Rather than take a half-dozen pages here, may I suggest you read chapter 23 Attic Ventilation in my book, _Complete_Building_Construction, 4th Edition pubished by Macmillan. See especially page 607 Ridge Vents and page 608 Baffles. This explains why we claim that only ridge vebnts with external baffles work.The validity of the years and years of research in Florida is reaffirmed by the research in 1995 at the University of Illinois.Gary Riskowski and Steve Ford with the Department of Agricultural Engineering in the Bioenvironmental and Structural Systems Laboratory, conducted a series of tests to compare the performance of different makes of ridge vents under different wind conditions.The following ridge vents wer tested: 1. Multi-Pitch Filter Vent. 2. Shingle Vent II. 3. Roll Vent. 4. Cobra Vent. 5. Cor-A-Vent. three styles of ridge vents were tested: 1. molded ridge vents. 2. Rolled ridge vents. 3. Corrugted ridge vents. Summary. Only the externally baffled ridge vents were able to create a negative pressure in the attic space and therefore an air flow from the attic exhausting through the ridge vent. The baffleless ridge vents took in air rather than exhausting it. To further prove a point, the researchers cut off the external baffle and the ridge nvent too failed to exhaust air from the attic.Contact the researchers at the University of Illinois or Air Vent800-AIR-VENT for a copy of the test report.My book's chapter on attic ventilation is based largely on the research of H.S. Hinrichs, whose paper "Comparative Study Of The Effectiveness of Fixed Ventilating Louvers."is published in the ASHRAE Transactions, volume 68, 1962. Available from ASHRAE. 800-5-ASHRAE. The reports on ridge vent testing has never been published , other than in my book, in any of the hundreds of books on architecture, construction, building that I have read. Indeed, read Fred L's #19 post this page. Finally, I agreed with Joe Fisco, that given the sad state of house construction: leaky ceilings, some ventilation is better than no ventilation even if the devices used don't perform as claimed. In otherwords, ventilation is a fail safe in case we screw-up. But as I have been arguing over the last 10,years sealing he ceiing is more important than attic vnetilation. IS Attic Ventilation Climate Specific?Indeed, attic vnetilating in wet, cold coastal climates is a No-no. In these climates the major source of moisture in attics is the moisture in the outside air brought in to the attic by ventilation. Higher ventilation rates increase the sheathing moisture content moisture and make for colder attics but do little to reduce the attic moisture content.Here is a case where ventilation is not only unnecessary but useless. However, house interior RH must be controlled by ventilation. On this subject see Forest and Walker's 1993 report, "Attiic ventilation and Moisture." Can be purchased from Canadian Moertgage and Housing corporation. I hope the clarifies things a bit. GeneL. Finally, I'd
*John,
Joseph FuscoView Image
*One approach might be to do what you think best and MONITOR the situation closely for a time afterwards to see how the roof is performing. Certainly you can make the gable end vents more waterproof.
*Well Joe, I guess you're right. I've only been around here for 6 months, and already I can see how these vent discussions go. Maybe I worry too much about the impressionable amateurs out there, or unseasoned professionals, when this topic comes up. I hate to see those comments on "venting police" go unchallenged. Also, the comment that fly-by nights somehow convince people that vents will cure all their roofing problems. Where I come from, its the fly-by-nights that don't worry about venting. They just want to slap some shingles on and collect their money. They won't be around if a warranty issue comes up. Vents are not a big money-maker for roofers. They would just as soon leave them off, and spend the time laying more shingles.I also get tired of endless references to "papers" on this subject,as if those papers mean a thing to a contractor or customer who faces a warranty claim. If studies have been around for 37 years that "prove" roof vents to be useless, there must be more to the story than an evil consortium of vent manufacturers bent on quashing this important development. Believe me, the vent industry is not that large and powerful.Since I don't much care for long winded posts on this subject, I'll sign off for now.John
*Nice breeze...
*Steve, et al. There is a common, widespread belief that power ventilating an attic makes a difference. It is claimed that the fans make are effective because they reduce attic temperature and , therefore, reduce air conditioning loads. Heat gain through a ceiling does contribute to a house's cooling load. Therefore, universities, public utilities, the federal government and others conducted studies in real houses to determine the effectiveness of forced atic ventilation in reducing cooling loads. They found that approximately 24% of the total calculated sensible heat gain was from the ceiling. Forced attic ventilation reduced the daily ceiling heat gain by 50%. BUT, BUT, this represented a reduction of only 7.9% of the total calculated heat gain of the residence. The University of Illinois researchers attributed the samll reduction in heat gain to the well insulated ceiling. They concluded"An analysis of the data...reveals that the addition of 2-inch thick insulation is considerably more effective in reducing ceiling heat gains than the maximum ventilation rate. When 3-5/8-inch is added the effect of ventilation is almost insignificant.Research by Doug Burch then with the old National Bureau of Standards(now the National Institute of Standards and Technology)"Summer Attic and Whole-House Ventilation , NBS special Publication #548, confirmed that power fans did lower attic temperatures, reduce the heat gain through the ceiling and into the air- conditionig ducts. but the reduction had little or no effect on the houses total cooling load. Repeated testing of homes with and without out powered attic fans used the same amount of energy for cooling, despite the wide differences in attic tempersature. When you add in the cost of operating the fan , mechanical ventilation is a net energy looser, and one still has a hot attic. I hope this answerts your question Steve. All these studies and research papers are beginning to "mean"something. CertainTeed now gives a 10 year warranth on their shingles applied to an unvented attic. It was a building scientist involved in studies and papers, who backed-down the hardboard siding industry. Any of you who remember the laws suits know that his research benefitted the buider and the home owner. It is up to those of us who understand the stuff to put it in a useable and understandable form so that builders and home owners can see how it benefits them. GeneL.
*Dear John,I know just what you mean. I hate it when somebody waves a well documented and controlled study in my face to prove me wrong. It took me years to come to terms with the idea that my experience could be fooling me.Now about that unvented roof warrantee thing: Neither you, nor anyone else we could find has ever heard of a roof failure claim rejected because of lack of venting. You made your case and it didn't fly, so it's time to get over it. And that other thing about venting not being profitable for roofers: Roofing Contractor magazine says otherwise. And I've got quite a bit of literature from manufacturers claiming that retrofitting their product is a real money maker. Of course I would dismiss those claims right along with their performance claims if they ever made any.Over it, Fred
*Fred,When did I say I never heard of a roof warranty being rejected because of lack of ventilation? Don't start putting words in my mouth big guy.
*JRS. In your 21.1 post you said, "If studies have been around for 37 years that "prove" roof vents to be useless, there must be more to the story than an evil consortium of vent manufacturers bent on quashing this important development." I am the one who is and has been citing the many studies on attic ventilation. Hinrichs's research is the only 37 year old research I quoted from. Nowhere in that report does he say that his research "prove[s]" roof vents to be useless." What he actually wrote in regard to gable-end louvered vents was "Gable end louvers are ineffective in producing air flow through the attic when wind is perpendicular to ridge." Hinrichs did all his research in a real house not in a laboratory. On the same subject I have said that with the wind perpendicular to the ridge that gable-end louvered vents are useless, or that they essentially stop working. As for your statement that "... an evil consortium of vent manufacturers bent on quashing this important development." I don't know what you are talking about. Yes I have said that manufacturers either know about the research or ignore it. However, they have never rebutted it. GeneL.
* Gene,
Joseph Fusco View Image
*Joe. Good hearing from you again. Did you receive my post about the BETEC Air Barriers Technologies II in Washington, DC on November 10, 1999? Although there may be a steady average wind direction, winds frequently shift direction as much as 30 degrees and often as much as 90 degrees within a few seconds. Obviously this shifting of direction has a great effect on the continuity of attic air flow .I believe that the word "When" in the phrase "When the wind blows perpendicular to the ridge," is self explanatory and acknowledges that the wind often shifts direction: When the wind blows perpendicular, or parallel or diagonally to the ridge. Indeed, Hinrichs further says "With diagonal winds, pressures at the soffit and gable end will in some cases counteract each other, thus decreasing the air flow through either louvers or vents."I hope this answers your question. GeneL.
*INSULATING AN OLDER HOME: I'm about to insulate my 75 year old home. The walls and ceilings are plaster and wood lath. I plan on doing extensive air sealing in the attic.My question is I'm interested in putting in cellulose - how to do this? Loose blown or dense pack? How can you dense pack an open (no floor) attic? If loose blown is done do you put down plastic sheeting first? Can I as a DIY'er do loose blown or dense pack?
*Actually Joe, the wind most often blows perpendicular to the ridge vents -- more than in any other direction. The roof plain directs approaching wind like a airplane wing, increasing its speed and focusing it right up the pitch and into the ridge vent. Natural convection has a rule whereby a small opening at the intake end and a large opening at the exhaust end of a convection stream increases the speed and therefore volume of flow. Therefore, for a ridge vent to work against other forces, its area of exhaust must exceed the area of intake of the gabel vents .. by, perhaps 200% or 300%. The wind approaching a house is sped up and directed into the ridge vent so the desirable flow of exhaust is reversed. A micro climate of chaotic air patterns will form in typically vented attic spaces.
* tedd,
Joseph Fusco View Image
*Venturi, not Ventura.The Ventura effect is most common in Minnesota, and it is characterized by blind devotion to a charismatic, if somewhat addlebrained wrestling personality.;-)
*I think Ventura Affect (as opposed to Effect) would be the the blowing by female breezes resulting in the Effect the Joe desires.Venturi refers to the speeding up of a flow of a fludi by narrowing the passage. This is not the same principal as modifying the intake and output areas of a convection stream. For a house to be a venturi, its convection intake and output diameters would have to exceed the diameter of the house.Haven't you heard of vertical wind sheer? Who cares what direction the breezes come from when its their behavior once they hit the house that counts.
*How about "Bernoulli effect"? (I don't remember exactly what that is, but it sounds good.)Basically the airflow over the house creates a low pressure zone downstream, high pressure upstream.
*I am beginning to think that gable end vents are the best way to go. If the ceiling is sealed well enough that there is very little moisture load and cellulose is used for insulation and blocking of radiant heat then very little ventalation is needed, only enough to dissapate small amounts of moisture that come thru imperfections in the ceiling air barrier. Maybe the fact that they don't work well is their advantage.
* tedd,
Joseph Fusco View Image
*JNohn - yes - it's not hard at all to d.i.y. cellulose. Home centers rent or loan machines. Read through posts in the archives for techniques - also at the Old House Journal board. Plan on your first day or weekend being a learning and experimenting time.You can't dense pack an open floor - but you close it with some housewrap and battens or similar low-tech means.Dense packing does require listening to the machine and feeling the cels pack - meaning it's time to draw the hose back a little. Probably figuring out how to seal hole for teh last few feet is the trickiest thing until you've done it once.Good luck and don't hesitate to post more questions.
*Hey Bill, you've been quiet for a long while. John, there are many discussion of diy cellulose in the archives, perhaps around last winter. Try "Search," esp. for articles by "connor" and "freddy."
*Hi Ron,I would be careful with gable end vents. They can get weather blown into them pretty easily if they are oriented into the wind. I just looked at an attic last month that had ridge vents, soffit vents and gable end vents. The gable end vents faced the side that got the prevailing weather, and there were black water stains all over the roof deck and rafters above the vent. Only there. Steve
*tedd. Your # 28 post is, for me,a bit confusing, somewhat incorrect, and scary.Wind prevails mostly from the west and north.Yes the wind flows over the roof as you mentioned. The scary part, if it is true of all ridge vents, is that the wind moves directly into the ridge vent... "so the desirable flow of exhaust is reversed.[Damn the cost, rip the ridge vents off the roof]. Years and years of testing at Construction Research Laboratory (CRL) in Miami, Florida, and at other facilities, shows that the scene you describe is true of ridge vents Without external baffles. Just how effective are externl baffles? I admit that there is no agreement among attic ventilation device manufacturers as to the need for an external baffle. CRL ran a series of tests of ridge vents with and without baffles, to measure wind-driven penetration into the vents at wind speeds of 50, 75 and 100 mph. The simulated rain rate was 8 inches per hour, the rate used for Dade Cunty, Florida evaluation. The water spray was added to the airstream upwind of the test speciment at a rate equal to 8 inches per hour of rain. In one series of tests at 50 mph lasting 5 minutes, water entered the entire length of the baffleless ridge vent and dropped down inot the atic space. The total water leakage was 1.5 quarts or 9 ounces per minute. Under the same conditions the extrernally baffled ridge vent allowed only 0.2 ounces of water penetration in 5 minutes, 0.6 ounces at 75 mph, and 1.2 ounces at 100 mph in 5 minutes. And so on and so on. Anyone wanting a copy of the test report send me 50 cents--stamps OK- and I'll mail you a copy.Thus it can be seen that baffleless ridge vents tend to be self-feeding when the wind direction is perpendicular to the vent. Air will enter the wondward side of the vent and be short-circuited to the leeward side of the vent. This prevents air movement from soffit vents to ridge vents.Ridge vents must be used only with double louvered soffit vents. There must not be other vents. Therefore, I asume by other forces you mean other vents in the attic. The combination of gable-end louvered vents and ridge vents is such that the ridgs vents NFVA far exceeds the NFVA of the gable end vents. (Unless the gable-end vents run the width of the house and from floor to attic). GeneL.
*Gosh darn you Gene,There you go throwing all that pointless data around again. How's anyone supposed to evaluate anything based on anectdotal evidence if you're gonna keep throwing facts backed by research into the mix?;-)Steve
*Cellulose: Is there much variance in quality of the type of cellulose on the market. I have already been told that there are some discount centers that sell a bag of cellulose wherein you can still make out and read tiny strips of newsprint! This would seem unacceptable. How can I tell if I am getting a high quality cellulose for loose and dense pack?I have heard of dense packing an open attic by battening down house wrap over the joist bays then dense packing the cellulose into that.How easily is this done and what advantage(s) does it confer over loose fill (preceded by air sealing) in the open bays?thanx, Johnnie in Wisconsin
*Joh. Csall the Cellulose Insulation Manufacturers Association toll free, at 888-881-CIMA and ask for Dan Lea. Or visit their web page http://www.cellulose.org. GeneL.
*I am an architect need to control marine air moisture intrusion into an insulated attic. The building is located right on the ocean shore in N Calif. Am considering eave vents combined with roof vents near the ridge. The insulation (currently fiberglass batts) is to be replaced with either blown cellulose or rigid foam. The ceiling is vaulted on the underside of the scissors roof trusses @ 24" o.c.. Thre roof is mission tile on plywood. Any comments / opinions / suggestions will be most appreciated.Thanksjohn [email protected]
*Joe and GeneIf you use a carburator you will know the design is to narrow the passage to increase the rate of flow of gas. A house cannot be a venturi since it has a larger diameter than the openings. I can't remember the name of the principle but when a fluid enters a small opening and moves into and through a larger diameter cavity (opposite of the venturi, it slows down and distributes throughout the cavity. The way to increase its rate of flow is to increase the diameter of the exhaust opening. This is contrary to the idea that one can increase the flow of fresh air by increasing the diameter of the openings on the windward side of a house. Same goes with close to ground cold air openings and second floor windows. Small diameter cold air intake will increase the rate of flow if the warm air exhaust has a larger diameter. For non-mechanical systems.Joe, You don't need to insult me. I though we was funnin'. The same principles apply passively to roof ventilation. The directions and velocities of air can be modified by louvres but when wind enteres the ridge after having been accelerated by the lift of the roof line (a nearly perpendicular flow relative to the the ridge, by the way), the ridge vent will not exhaust the attic air. If the gable or soffit vents have a larger area of intake than the ridge, the tendency of the air stream will be down, not up. Since there is generally more area of soffit ventilation than ridge ventilation (and worse so with added gable vents) the design is inherently contradictory.If louvers direct the roof-top wind stream through and upwards from a ridge vent, then the design could "pull" attic air and this would draw in soffit and gable vent air to flush the attic. This wold not be a venturi, it would be a draftting effect. Perhaps a ridge vent could be designed incorporate a venturi in its louvered pathways. I would say that gable vents would be counterproductive in any case and stick with the soffit vents since they make for too much intake diameter that would disturb the draft, the lift and the convection stream. This is a convection stream, whetaher you like it or not and a convection stream can be modified by changing the shape and diameter of the intake, throughput and exhaust openings and pathways of any stack or convection stream. This is hardly tripe and essential to the design of low cost, passively cooled and heated buildings and as well as fundamental to mechnaical HVAC systems.
* tedd,
Joseph Fusco View Image
*tedd. A ridge vent might be likened to a bumble bee. According to aerodynamics he can't fly. But because he is ignorant of these principles he flies...and thus the ridge vent works. GeneL.
*Dirk,This venting method seems to defeat the cost you will be paying for the Icynene. I too thought about creating a "channel" under the roof deck - but after careful consideration opted not to (at least as of yet - I have NOT applied the insulation). I am still considering the Icynene an also a closed cell product (I am waiting for the installers info....). I would appreciate any additional thoughts of yours too....
*Keep in mind the Dollars/R-value/Square foot cost. Icynene is a good product and I do use it where I feel it is the best choice but it is expensive and doesn't have the R-value of PUR. Keep us informed on the prices in your area.
*Gene,
Joseph FuscoView Image
*When the wind blows, the bumblebee stays indoors.Are you saying that the attic space, even when its environment is sealed from the building's interior space will have a postive pressure (without mechanicals)? How is this possible ? If it were true, then air would be exhausting via the soffits and the ridge vents. Do you mean a negative pressure caused by drafting across the ridge in which air is streaming in through the soffits to fill the void. Or maybe its a postive pressure from wind lift up the walls an into the soffits and filling the attic an exiting the ridge ?Can't compute but open to instruction (not insults) ...tedd
*Here Icy is $1.75 sf for 2x6. That's about R-19, and probably a truer R-119 than fg because of even coverage, airtightness.
*Andrew,How much is PUR in your area for 2x6 and 2x4? Was the Icynene price for a nominal fill or a compleat fill with trimming to flush with the studs?Ron
*Icynene was a complete job I believe. The trim pieces can be used in the attic too, maybe mix 'em with cellulose? No one I called locally had any idea what PUR is; I believe EFI sells it and I plan to look into it to get some numbers. 50 cubic feet (or 600 "board feet") costs $600 from them, presumably R-7/in. So for an R-14 wall -- 2 inches of PUR -- it would be somewhat less than $2 sf if I undestand correctly. Pricey too, and there is a question (raised by the Icynene people) what happens to the seal as the framing shrinks.
*The PUR with framing shrinking sounds like a question for Gene L.
*Fred, On the issue of cellulose composition. Chunkier is better? I got that from your post anyways. A commercial cellulose installer told my buddy not to buy the coccon or other hardware store brand (Blowes, Home Deport, etc.) because the fire retardant is Aluminum something or other. It causes corrosion on copper pipes and does not deter insects. He said the "commercial grade" stuff uses borate which also deterrs bugs and causes no corrosion.As far as I can tell the aluminum would be anodic and the copper would be the cathode. So while there would in fact-be an oxidation reduction reaction it would actually be reduction occurring on the copper pipe (Aluminum plates out) as opposed to copper going into solution. Care to comment.Is i better (from a product application point of view) to blow cellulose in the winter? Assume the blower is outdoors and the installers are iso-therma
*Geez, someone spent too much time in chem class! The Cocoon has boric acid in it and I'd tell you the fire retardent if it didn't require me to go outside (it's cold out there!).
*JRS. We heard of lots of leaking problems with "hidden"ridge vents that are alleged not to leak. In one case external baffles had to be provided to stop the leaks. GeneL.
*Hello Gene,I'm a little curious about what prompted your remark today. My last post on this thread was Sept. 10. I have used concealed ridge vents since 1989, on more than 500 roofs. I have received no complaints from leaks with these ridge vents. In addition to the mfrs. warranty I include a 5 yr. workmanship warranty on my roofs, so when a problem crops up I do hear about it. Before '89 I used Leigh's aluminum ridge vents(no baffles) and the problem I had with these was that the joints between the 10' sections would invariably start leaking after 3-5 years, requiring a repair to the joint. This was one reason why I was eager to try the concealed vents(one other reason being for the improved appearance) I can certainly envision scenerios that could result in vents leaking-such as hurricane conditions with sustained high velocity winds blowing in conjunction with huge amounts of rainfall-but we don't get those conditions here in NE Ohio. I wonder if even baffles would be able to keep water out in such conditions?John
*what are you guys talking about when you say "concealed ridge vents"?is that the same as a "shingle-over ridge vent"?..i had the same problem as you John, i was using Air-Vent alum. worked great, then the joints started leaking about 5 years down the road..some of the smoke testing i've seen and the test data convinced me that the only ridge vent i will buy, install , spec , or recommend is ShingleVent II , .. which is a shingle over vent with a baffle, built-in end plugs, and a filter fabric......but i was curious,too, Gene, why you resurrected this thread?
*Hi Mike,Concealed ridge vents are shingle-over or cap-over ridge vents. I use Everflow and Ridge line. Cobra vents are popular here, but I don't like the "soft" surface they create. You never dare step on them, and even sitting on them will push the vent down, while the nail stays firm at its original hight. Crushing is another reason why I don't like aluminum ridge vents.John
*JRSI am in Rochester, NY and I didn't think we were in a "high wind area" either. But in spring and fall we routinely get 45 - 70 mph winds.Two weeks ago we had sideways rain, 54 mph wind from the west. I was outside and noticed no water was dripping off the west side of my as-yet gutterless metal roof. The wind stopped briefely and water deeper than the 1" ribs gushed off the roof in a rather comical deluge. The point - the wind was pushing 100 or so gallons of water up my 4/12 metal roof, so I am glad I caulked the heck out of the filler strips for the hips and ridge, and I'm also glad I forgot to add the vented ridge.-Rob
*Gene's power works in mysterious ways. I don't think we need question his ways. 8-)-Rob
*John et al. I've long wanted to say something about hidden ridge vents, and reading John's post triggered a response. The strange thing about this business is that some of us swear by a product while others cannot stop swearing at the same product.When Air Vent introduced its Shingle over vent I switched from their aluminum to their plastic vent. I never in twenty years had a single complaint about leaking vents.But I always supervised the installation of these vents.When I was Code Enforcement Officer I was in monthly contact with attic ventilation manufacturer's reps. So I was getting lots of feedback about what was working and not working. I was privy to the testing results of many of these vents in Dade County,Florida. From the testing labs and from the reps I learned of the substantial quantities of water taken in by some of these hidden vents. In one instance external baffles had to be furnished to homeowners to reduce the water intake. Indeed, it was from builders that I got the negative information against drip-edge vents.However, the technical engineer at one attic vetilation manufacturer warned me not to buy any drip-edge vent including the one made by his company. I saw with my own eyes the damage caused by drip-endge vents.My findings were supported by one of the biggest house builders in the USA. Today, I recommend only the ComBo Vent for a drip edge vent. This vent is now called the Smart Vent and is manufactured by Globe 800-473-7151, and distributed by ABC Supply Company 800-366-2227. ABC calls it the Intake Vent. What this taught me was that we put too much emphasis on attic ventilation by asking vents to do what they are not designed to do. This led some years ago to my stating that the first line of defense against ice dams begins in the basement.Customers complain only when they discover a problem. But it may be years before they notice the problem. Thus the builder is able to say i don't have any compllaints. The tens of millions of dollars of ice dam caused damage should be telling us something.GeneL
*
I have a house at the beach and I am concerned about proper attic
ventillation. Presently, there are three gable vents, a continuous soffit vent,
a powered attic fan, and two 10" by 10" vents that appear to be abandoned--one
was damaged in a hail storm and admits water into the attic. The last two vents
I would like to remove. I am also getting water infiltration through the gable
vents. These are just some off-the-shelf wood gable vents with no special
severe-weathering characteristics. These too I would like to remove. I want to
install a continuous ridge vent in their place because I am convinced I will get
superior ventillation. Is this correct? Also, what type of ridge vent do you
reccommend for installation at the beach. Lastly, If I decide to leave the gable
vents, are there better performing gable vents than what I have. The house has
fiberglass shingles and hardiplank siding.