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I have an old house with an open cornice roof overhang which does not allow the use of any type of soffit/eave intake vents. I would like to install a ridge vent but don’t know how to provide a proper ait intake path. Gable vents are out of the question (it’s a tudor revival style house). I am considering some sort of powered fan with external intake ducts that would blow air into the space behind the knee wall of the finished attic (the air would be exhausted through the ridge vent). Has anyone had experience with this type of thing? Will this type of system work to property vent the roof?
Thanks!
Replies
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Narendra
You came to the right/wrong place to ask that question. Before the sh*t hits your attic fan dig into the archives here at 'breaktime' and read up on attic venting . . .there's a lot to read.
enjoy ;}
-pm
*Narendra. In addition to consulting the archieves, see Chapter 23 Attic Ventilation in my book, _Complete_Building_Construction_, 4th Edition published by Macmillan Publishing Company. Check Barnes & Noble. I fhtye have it you can read it free in their store.GeneL.
*living nextdoor to a firman for 9 years i would hear many bad stories of electric or thermostaticial controled atic venting units. the problem is in the heat of the day the unit gets hot then kicks on and gets even hotter properly installed there ok:::but make SURE THAT THERE INSPECTED AND MEET CODE!!!!!!
*Seems to me without intake you'd be intaking from house leaks, sucking warm moist air. Not a good idea.
*narenda...i don't neccessarily agree with your supposition that you can't provide an intake path thru the open cornice area ...if there is a cornice.. it can usually be modified to allow some type of screened venting.... it may be more work thatn you want to do.. but it can be done..and would undoubtably be superior to the power intake you're thinking of...
*Narendra. See Norm Kerr's (2) post-in Energy, Heating. Insulating & Venting for October 29, 1999.Mike. Screening use for soffit vents is generally a NO NO. Is the screening 70% open or &0% closed (14 threads to the inch)? The best solution in these cases may be the ComboVent now called the Smart Vent, available from ABC Supply Co.Inc 800-366-2227.Fans will short circuit the ridge vent. Ridge vents must be driven by soffit vents. Remember, not all combinations of ridge/soffit vents work. GeneL.
*glad you qualified that Gene, a NO-NO,seems to me Narendra is talking about something that is architecturally significant...someplace in that cornice , if it is reworked and redesigned, there should be room for a continuous one & half to two inch slot, with Bronze screen....since ridge vent II is primarily a PULL type vent, the continuous screened soffit in the cornice should provide the balance needed...if the choice is between something that MAY be ugly , and thus NOT get installed , or something that can be worked into the architectural detailing and thus WILL get installed, my choice is clear....
*Mike. Once again I want to emphasize that one msat be certain that the screening is 70% open: ask how many threads per inch. If there are 14 threads to the inch the screening is 70% closed: only 30% of the available air will enter and thus cause ridge vent reversal. Remember how hot it is in a screened tent?GeneL PS. I understand that FredL is no longer with us at BT?
*didn't get that part of the advice from your first post.. but the one about 14 threads per inch now makes sense...as far as FredL... he ain't been around... and i do miss his input....much as i disagreed with him..now the only fun i have is arguin with you....i was hoping his article in FHB on cellulose insulation would be more boundary stretching , but it seemed like the plain vanilla version for the new initiates...guess i wanted more fire...not to worry, he's only a click away
*Mike. In the Thermal Performance Of The Exterior Envelopes Of Buildings VII, there is a paper, "Organic Insulation Materials: Effect On Indoor Humidity and Necessity of a Vapor Barrier,"by Carsten Rode, that might interest you. The author seems to suggest that under certain conditions, even with a wll full of cellulose insulation, a VDR may be necessary.Sorry if at first I didn't clearly explain my objection to screening for soffit vents.GeneL.PS. In one post the writer suggested that FredL and GeneL might be the same. Good grief. The writing styles are so obviously? different. I too miss him, but have you noticed that some posters are still attackers? His abcense hasn't lessened the uncalled for acidic remarks.
*Freddy casts a long shadow.Rich Beckman
*GeneL.. i don't have access to that paper...what is the gist of it?...i just did a thread count on our bronze screen, it's 14 to 16 threads per inch..but i can't conceive of how it can be 70 per cent ...i'd wager that if a free moving colum of air were blowing across a surface, only 30 per cent might make it to the other side of the screen placed at right angles to the flow... but i find almost zero constriction of flow in a vacumn set up.. ie.. if i place the bronze screen across an inlet being evacuated by a vacumn cleaner the difference would be less than 5 per cent vacumn.. this is what i am talking about in saying that ridge vent air flow is a pull type flow... and i contend that a soffit vent will supply the required air.. another example would be Freddy's blower door... if i set up a blower door and put a 14 count screen door in front of it .... will it exhibit the behavior of a 70 percent closed door?hmmm?...i think the positioning of the soffit vent in the soffit (ie: closer to the fascia...or closer to the frieze)... would have more effect than the screening...don't you think the filter fabric in Shingle Vent II as the same restriction as a 14 count screen?but tell me more..b but hey, whadda i know?
*GeneFred deservedly lost a lot of credibility here when he started deleting his posts. He lost what was left when he demonstrated childish petulance by going back into the archives and deleting all those posts as well, and he further tarnished his rep. by changing his name to "." so that deleted posts wouldn't be identified as his.He managed to draw many threads around himself, and then gutted them by deleting his posts. Quite the agenda!I don't know which acidic remarks you are referring to, but he certainly deserves any that I send his way. He brought way too much baggage to this forum.. . I don't miss i him at all.regards-pm
*My information on the screening came from engineers who measered the air flow through screening. One of them was Hank Spies--now retired--from Univesity of Illinois. The other engineer, now retired, was technical director for an attic ventilation devices manufacturer. Air flow measurements through the fiberglass filter shows little or no restriction of the out ward air flow. the location of the soffit vents in the soffit is crucial. But little or no attention is paid to this.As H.C. hinrichs note almost 40 uyears ago, "Their is very little possibility of damaging infiltration in the soffit area if the openings are adjacent to the fascia annd a minimum of 8"from the side wall of the house." More laterPatrick. Sorry for lack of clarity. The acidic remarks I refere to were not directed to Fred. So, even id he is gone, the uncalled for adhominem attacks will persist.Are you familiar with the new http://www.NoRTH-RTHN.org web page? GeneL. Did you know that the pumping or suction action of a baffled ridge vent works independent of soffit vents? More later.d
*GeneTypo on that website? Small case doesn't work either, unless it's http://www.northern.ca???-pm
*Narendra,Let me start with a question that may seem really stupid at face value. Why do you want to vent the roof? You say it is an old house. Is the roof still sound? Is the roof rotting? Or is it comfort you are looking for? Are the upstairs rooms too hot?-RobP.S. - Just spent a week with Fred at Affordable Comfort in Ohio. He split is room with me due to my late registration and the fact that all the rooms were booked. He is one of the nicest, smartest people you will ever meet regarding anything, not just building science. We spent many hours talking shop with many other people that were there as well. After finding out what he knows, and talking with the people he associates with in this field, I am surprised he even chose to argue these things with these people. Sadly the sides he takes have been proven as fact for over two decades, both in the lab and in the field.Fred removed all of his posts due to his realization that the content of the threads began to disturb him and were so far removed from education to be meaningless. He came to this realization when his son was reading one of his posts. He (and many others) has serious disagreement with the way FHB editors are running the site.I may be the closest thing to Fred Lu left here. But I have even less time to argue over reinventing the wheel with people who still think we don't even need wheels, much less they be round.
*Double dittos and amen.PS Robb: I'm jealous - I couldn't get away but will try again next year.
*Bill - It was worth every penny. I was like a kid in a candy store, I couldn't take in enough information. The contacts and friends made nationwide have already paid off. It gelled every counterculture idea I've had relating to building science since my teens.The down side is that I am even more critical, angered, cynical and disappointed with the state of residential construction. It makes much of the "energy efficient" anything seem even more laughable. At least now I can argue from fact and first-hand experience. Though, as I have said before, I can't type for nothing so the last place I intend to argue is online!! Besides, I'm too busy consulting, diagnosing building failures, and doing inspections now.-Rob
*Patrick. I typed in the URL just as I posted it: http://www.NoRTH-RTHN.org and it came up. But afterbthat I had some trouble. You can contact Darrel Smith(about the web site)at CHMC. He's in the Research Division.If you do contact Darrel, pleas e let me know how you learned.Rob. Glad to hear you're busy. GeneL.
*Don't miss FreddyL's misinformation the least bit.A lot of roof venting, regardless of the type, fails simply because it's not designed specifically for the house in question. Everyone uses the cookie cutter design of ridge vent/soffit supply because it's too much trouble to design or adjust venting to suit specific needs.The original poster, in this case, did not supply enough information or dialogue to allow anyone to give an intelligent answer to help solve the problem with the ventilation.But that didn't stop the brown nose destruction crew from putting in their 2 cents worth.A lot of bozos are hell bent on eliminating venting because they don't understand it's role in healthy homes.GeneL, someday you'll shock me by actually answering the question asked by a poster, in an intelligent fashion, without trying to peddle your book. It hasn't happened yet.Gabe
*How stupid were my questions back to her?-Rob
*Gabe,In your post you say: A lot of roof venting, regardless of the type, fails simply because it's not designed specifically for the house inquestion. Everyone uses the cookie cutter design of ridge vent/soffit supply because it's too much trouble to design or adjust venting to suit specific needs. I need a vent design for a specific existing (1920s) house up north. It is near an airport, and the repairs are being paid for using air travel tax dollars. The home has to be quieter after the work than before, so the number of penetrations has to be absolutely no greater than necessary. It has a tile roof, felt paper below, board sheathing (butted), all hips, no overhangs, and a gutter covers half of the fascia depth. The ceiling is not airtight, there is a hole for passive air movement between the bathroom and the attic, and there are presently no roof vent devices. There is some blackening of the underside of some of the sheathing, but there are no signs of viable mold spores.Quiestion 1. Vent or not? The client wants to do everything possible to reduce the noise and demands strong justification for any new holes made in the envelope. Would tightening the ceiling plane be sufficient, along with bthroom vents to the outside? What is the difference in moisture load to the attic from a ceiling-tightened house versus one without tightening (the client asks me).Question 2. If vents, what design air flow--based on what assumption about moisture source? What are we aiming for in terms of performance? Mechanical or passive vents? How to size vent openings so that the opening area is the bare minimum for the load? Are fascia vents okay? What design? Passive vents require much more opening area than mechanical for the same estimated dilution flow, which is very undesirable in terms of noise.Question 3. If mechanical, what direction, in or out? Exhausting fans risk pulling moisture from below, especially without overhangs. Intake fans use pressure to restrict moisture flow into the attic from below, but may need maintenance of exterior screens. What controls (or continuous operation year-round)? What makeup openings, and where?I am sure you could provide sincere and good answers to these questions, and so could I (I have to!), and our answers are likely to differ, which is okay. My point is not to get into the details of this, but to challenge your assertion that specific venting design can and should be done on individual homes, and to present a difficult case. In particular, how do we find the crossing point where one constraint, say moisture, could argue for larger openings and another constraint, say noise control, argues for smaller openings or none at all?
*Hi Bill,The first thing that comes to mind is dividing the project into relevant tasks.The first being the bathroom venting.The second being sound attenuation.The third being whether or not to vent the attic.Item 1. The living areas envelope is being compromised by the passive air movement between the bathroom and the attic. Assuming an average lifestyle, by the owners, during times of heavy use, (showers etc.)it would be reasonable to expect moisture beading on the ceiling and walls during these activities. Even if you can't see the mold, it certainly doesn't mean it isn't there. The bathroom would have mold spores. A mechanic exhaust would be a must and the ceiling sealed. I would hope that the main dwelling would have an air exchanger and be completely sealed.Item 2. I have trouble imagining a better roof for sound attenuation than a tile roof. So the emphasis should be limited to the building envelope with special attention to the windows. Simply by replacing the glazing with a heavier glass will dramatically effect the sound proofing of the house as would ensuring that foam was installed between the windows and the framing.Item 3. Tile roofs are ventilated by shape and installation. There is no need to ventilate the attic for the benefits of the tile, unlike flat asphalt shingle. The attic itself is another matter. This is probably one time that I would consider a mechanical air exchange system for this area.Chat laterGabe
*On a scale of 10 on the stupid meter, I'd give you a 7.Gabe
*I don't get it:"Why do you want to vent the roof?" - 7 out of 10 on the stupid meter."The third being whether or not to vent the attic." - reasonable issue to resolve from a seasoned expert.BTW - Bill R, where is the house? Is this part of that Minneapolis or Wisconsin deal where these multi-thousand homes are all getting redone. I am surprised that the prescriptive and non-climate specific code of your choice doesn't help here.Is that to say that codes should be more climate specific?Or should they be more performance oriented?Physics provides very clear answers to your questions despite their absurdity relative to the conventional wisdom.-Rob
*Because the poster didn't ASK for comments on the validity of venting but on HOW to do it properly.I gave you a 7 on the stupid meter so that you would have room to raise the benchmark and you never disappoint me.Gabe
*Rob - it seems Gabe doesn't think much of your question. Perhaps he knows what building problem the poster is trying to solve without knowing climate or any other particulars. Could be one system fits all. Let me know how it comes out - I don't read his posts.
*Gabe. At least you are consistent. Once again I ask you why you claim my responses ALWAYS:-} contain a reference to my book? Why do you fail to mention the mnay books, research papers and so on--written by others-I refere posters to? GeneL.
*Rob,You ask: BTW - Bill R, where is the house? Is this part of that Minneapolis or Wisconsin deal where these multi-thousand homes are all getting redone. I am surprised that the prescriptive and non-climate specific code of your choice doesn't help here. Well, I don't want to be too specific, but you're on the right track, and it's not one home by any means. I'm not surprised that you're (not) surprised that prescriptive and non-climate specific codes don't help.For me it's a physics question, not a code question, but that doesn't simplify matters too much. All of the inputs (moisture source load, exposure to wind,...) are probabilistic rather than deterministic, so the results are never guaranteed. We've been spoiled by the determinism of the building code. Compliance doesn't guarantee performance, and non-compliance doesn't guarantee non-performance. The determinism of the code masks the crapshoot of performance in the real world. You know all that, why am I going on?
*Then have someone else read them to you so that you can learn something.Gabe
*Gene even in your rebuttal you mentioned that you have a book.Consistently yours,Gabe
*hey, far be for me to but in.....BUTwell gene, i'd agree that gabe don't play with kid gloves... but he did get u in yur last post....hmmmfair... nah.. but anyways i got ur book...i'm waitin for gabe's .. i think it may be more amusing.... your's was rich in facts, but light on humor...what the hell was this thread all about anyways?oh, yes... i still like my idear.... now u got my curiosity... i gotta find someone with some equip.. i can't believe that a 14 count screen has a 70 per cent restriction...something rotten in denmark..
*I'm glad you were going on, it was refreshing to hear someone else who understands.Regarding the probalistic vs. deterministic. Physics is always right. Stop the mechanisms that drive heat and moisture flow and it will work every time. This is a fact. A blower door test can tell you how well you've achieved isolation of the living space from the exterior.-Rob
*If I had written a book that people could get for free through their library system that had 20 pages and a dozen illustrations dedicatedto the topic, I would referr people to it. Seems alot easier than typing it here. Hell it might even educate them a little bit if they accidentally opened other chapters.I believe, as reported in this thread, uneducated consumers is a problem in this industry. People don't know enough to pay for quality. Though I suspect some people pray on that ignorance,and the consumer pays for it anyways.-Rob
*But what if there were no need to do it?What if it wouldn't have the intended result, even if done properly?Would it have been worth the hassle?-Rob
*Mike. As I noted in my post to you, the information on 14 threads to the inch came from Hank Spies formerly of the Univ of Ill's Building Research council. I will attempt to contact both the engineers I spoke of and will post you soon as I reach them.However, it is common knowledge that screening reduces the NFVA of vents. The reduction ranging from 25% to 50% depends on the number of wires per inch.You might find H.C.Hinrichs's comment interesting: " Ïndividual soffit units will not produce the same protection[from rain and snow penetration]as continuous soffit ventilation even though the same net free area is provided." GeneL.
*yes i cud see some type of venturi effect from individual soffit units as opposed to continuous vents of the same NFVA....and i know that screening REDUCES the NFVA,, i just don't believe the 70 per cent value....
*Mike. Still waiting to hear from engineers.One I spoke with said he couldn't remember off hand who has actually measured the airflow to determine how much of the screening was opened and how much of it was open.However, in the meantime take a 16 mesh screening. This mesh has a wire every 1/16th of an inch. Assume a wire diameter of 20 mils. Now shove the wires all togethr to one side of the one square inch opening. Now measure the opening that is left. Result is the % of the opening vs the % of the closed section. Remember that even if the mesh allows say 70% of the available air to enter, screened vents in active areas, lots of dust and what have you--not to mention that they often get painted-- the big worry is the clogging of the screening. I have seen peg board(1/8-inch diameter holes on 1-inch centers)completely clogged, first by paint,and finaly by dust and insects. The result was total failure of the ridge vents. Hope this helps. GeneL
*One of the big things I've learned in remodeling is after the customer tells you what they want, you shouldi alwaysask why they want it. Customers often think they are going to solve a problem when in fact what they want to do will have no effect or make it worse.Gabe, a consistent theme of yours is that one solution cannot fit all situations (although venting seems to always be the answer) and that people who post with answers without the needed additioanl info are blowing smoke. Then you call someone asking for additional info stupid.Rich Beckman
*Mike. Still waiting for reply from engineer. One thing I forgot to mention that plays a large part in reducing the NFVA is the friction the air meets when it contacts the metal fibers. After the screening is fabricated it is then galvanized. this createsa rough surface. All these factors combnined lead researchers to say the screening reduces the louvered vents NFVA by 50%. Believe it or...not. GeneL.
*Wrong Rick,I never call anyone, who is asking honest questions, stupid, I only call someone who knows better and is being stupid, stupid.The design of a proper ventilation is a one on one situation. What works for one may not work next door.Yes, I am consistent with regards to proper ventilation. The future points towards 20 year warrantees for homeowners. Good luck to those who don't understand the mechanics of housebuilding.Gabe
*Well, I am still a bit confused why one should take ani oldhouse and automatically add venting to the attic without first determining whether the lack of venting over so many decades had caused a problem or not. In that circumstance, asking i whydo you want to vent is an honest question, and if you can't see that, I'm sorry.A lot of people liked to blame Freddy for poisening the threads, and Lord knows, Freddy injected a lot of toxins. But Freddy isn't here, and who is injecting toxins now?At least you admit that you called the questioner stupid and not the question.Rich Beckman
*Rick,Why would you automatically assume that the poster doesn't know what they want?Regarding the mechanics of the house in question, it's quiet possible that the attic is already vented by other means or flaws.Someone calls you to give them a price for adding ventilation to their house, I have difficulty in beleiving that you would simply tell them that they didn't need ventilation without first going to site and seeing for yourself.As responsible contractors, first we listen to the clients requests, next we investigate the situation and only then, do we offer them the benefits of our experiences if we think that they are doing down a futile and expensive path.But in the end, we do what we are contracted to do and to the best of our abilities.It's not uncommon for me to install something that I beleive is not required but it would be unthinkable for me to do so without bringing it to the attention of the client, first.You see, my friend, it's quiet possible that I might be wrong and the client might be right.Gabe
*And why would you automatically assume the posteri doesknow what they want?I don't recall anyone saying that the poster doesn't know what they want. The original "stupid" question was "Why do you want it?"It is your intentions to argue that open discussion of the situation is bad? 'Cause that seems to be the case right now.Yes, the questioner might be wrong, and the client might be right. Maybe Narendra would answer the "stupid" question with "I want to vent because the underside of my roof deck is wet and rotting and that weatherization contractor told me last year when he sealed the attic floor that that would fix it"> It's not uncommon for me to install something that I beleive is not required but it would be unthinkable for me to do so without bringing it to the attention of the client, first.Do you think that attic floors should be sealed? Wouldn't you want to perhaps bring this up? Even when you are certain you already know the "why", it is a great question to get the client talking about the house. And a good discussion is the best time to bring in other ideas (like sealing the attic floor) without the customer feeling like you're simply selling extras rather than selling stuff the customer needs.> Someone calls you to give them a price for adding ventilation to their house, I have difficulty in beleiving that you would simply tell them that they didn't need ventilation without first going to site and seeing for yourself.Only one post in the thread is suggesting not to vent. And that is RJT in post #4. And he is simply saying venting without supplying intake is a bad idea.> As responsible contractors, first we listen to the clients requests, next we investigate the situationIsn't that what the "why" was part of...investigating the situation. Do you really go to client's homes and get hired to do things without asking "why". Maybe to reroof when the current roof is visibly deteriorated, and I'm sure there are a few other situations. But if I get to the house and the customer says "I want to install a ridge vent", then I want to know why. There is a near certainty that at the very least, there is an interesting story here.> I have difficulty in beleiving that you would simply tell them that they didn't need ventilation without first going to site and seeing for yourself.Again, no one has told anyone that they don't need ventilation. But you've told BillR to ventilate his attic "This is probably one time that I would consider a mechanical air exchange system for this area." without "going to the site and seeing for yourself." You did this on the basis of an exchange of a lot of information. Not visiting the site is one of the limitations of this forum. But that hasn't stopped lots of people getting lots of good help, usually on the basis of a lot of information exhange. "WHY?" is often an important part of that exchange. You are on record for saying that "WHY?" is a stupid question. I still have trouble believing you really think that.Rich Beckman
*Rick,maybe who have been too busy challenging my response to notice that since the original post, Narendra has not made any comments or clarifications since. The only posting have been with regards to the hyperthetical and not to the actual case at hand.Remember, you already agreed that I never called the question stupid only the individual for his actions.GabePS how about keeping your posts a little bit more to the point and cut back on the volume of rhetoric.
*Gabe,> since the original post, Narendra has not made any comments or clarifications since.Yes, I noticed. But I don't see the relevance.> The only posting have been with regards to the hyperthetical and not to the actual case at hand. Yes, I know. But I don't see the relevance.> Remember, you already agreed that I never called the question stupid only the individual for his actions.So you're saying that you have considered it a good question from the moment you first saw it? Or since when?Hope this is short enough for you.Rich Beckman
*Narenda has also not replied to my E-mail message from the day she posted the question. This was alos one of Fred's dislikes of the board. The fact that people would post a question and apparently never check it again. There were threads that posters left entirely unresponded to. But I digress.I was trying to get all the information to comment on the case at hand. I have not yet recommended anything.My original action was asking the question "why"!!!And in closing - since the person who posted the question doesn't give a hoot then neither shall I anymore. See Ya on the next thread.-Rob
*Mike. The BOCA code requires that ventilation openings be covered with "corrosion-resistant mesh...with openings not more that 1/2inch in any direction." The 1997 Uniform Building Code requires 1/4 inch mesh. However, a builder or home owner wanting smaller openings, insect screening, could find himself in serious trouble if he doesn't know how much of the screening is open and how much is closed. Here is an example. Mesh is the number of openings in the wire cloth, in each direction, per lineal inch.What follows is not theory but is based on the actual manufactured screen. A 16 mesh plain weave wire cloth has a wire diameter of 0.0320 inches. The net clear openng of the mesh is 0.0310 inches which means that the percentage of the open area (in one square inch) is 24%. In other words the screening is 76% closed. The gross openig is 0.0625 but is measured from the center of one wire to the center of the next wire.Thus when the wire diameter is considered the actual clear opening(before galvanizing)is 0.0310. Squaring the opening dimensions gives us an area of 0.000961 square inches. Now multiply the number of meshes, 256, times the area of each mesh and we have a total area in one square inch of 0.246 inches.This is, as a percentage of 1 square inch only 24.6 percent.Thus the screening is 75.4% closed.Keep in mind that the mesh is galvanized after it is manufactured, thus there is an small decrease in the dimensions. The air movement is furhter reduced by the friction of the air passing through the mesh.The 14 wires to the inch I mentioned, has fewer wires than a 16 mesh but nevertheless the percentage of the opening is only 30.5%: 14 mesh, wire diameter 0.0320, clear opening in inches 0.0390, and percentage of open area is only 30.5%. I hope this clears up the doubt and keeps you on your toes about the mesh numbers.GeneL.
*Gene..don't know wer u get yuur numbers from.. and so i can only tell u wat i find..we use a heavy duty Bronze screen that we buy from the marine supply store.. the mesh is 14x18..and i confirmed that by measuring a 2x2 section and counting..then i took 28 strands and aligned them on a smooth surface, and compressed them so they wud not overlap.. but they wud touch each other..28 (enuf for two inches) measures 12/32 inch or .375 inchdivide by 28 = .0134 for the diameter of the wire so.. if i have one sq. inch my 14 count is going to cover .19 of the sq. one wayand my 18 count is going to cover .24 of the square the other way ..leaving me with a rectangle measuring 0.76 x 0.81 inches of FREE space.. or 62 % of the space will be (((( Net Free Area.. )))) = 62 %now.. that does NOT take into account friction.. but if you take a piece of screen and you inhale thru it.. you will not feel the least restriction..so i am more confident in my number of 62% NFA than your's of 30%when we do architectural screening, we make up all of our venting before we screen, then we prime, and then we finish paint...THEN we screen..then we install the vents..we use bronze screen which even in this salt enviornment i feel will last 50 years.. and if someone is going to come along and paint our screen shut at a later date... well, shame on them..so, what can i say? maybe someone inverted a number?
*Mike. My information came fromCross Wire Cloth, a manufacturer of woven wire cloth. The numbers are theirs. They are located in Bellmawr, N. J. GemeL.
*"Believe nothing you hear, half that you see, but all that you do." (a favorite saying of my high school English teacher). Mike I think your numbers seem reasonable.
*yee gods crusty u don't know what a relief that is .. i've been sitting here waiting with baited breath for someone to tell me just that..how cum it took u 6 weeks to cum to my rescue ?so.. gene.. take that !
*
I have an old house with an open cornice roof overhang which does not allow the use of any type of soffit/eave intake vents. I would like to install a ridge vent but don't know how to provide a proper ait intake path. Gable vents are out of the question (it's a tudor revival style house). I am considering some sort of powered fan with external intake ducts that would blow air into the space behind the knee wall of the finished attic (the air would be exhausted through the ridge vent). Has anyone had experience with this type of thing? Will this type of system work to property vent the roof?
Thanks!