Building Science Insights: To Vent or Not to Vent

hi my name is Joseph stearic I'm a principal with building science corporation out of Somerville Massachusetts I'm an engineer and I deal with heat and mass transfer building science building physics and I'm here to do a presentation on to vent or not to vent that is the question well hello everybody let's let's start to vent or or not to vent I don't actually look like that anymore the Photoshop this is perhaps the most underappreciated assembly we have in the building industry it's a vented attic it's absolutely magnificent there is no better way to build a roof assembly than to have a vented attic there are only a few things that you have to do correctly to make this work in every climate zone in the world you want your ceiling plane to be absolutely airtight we don't care about vapor tight we just want that ceiling plane to be absolutely airtight then what do we want to do we want to have lots of holes down low and a few holes up top you don't want to have lots of holes up top and few holes down below because you don't want your attic to suck right because if your attic sucks and your ceiling is an air tight you're sucking air out a lot out of your house and that would suck right because the air that you pull out of here is going to be replaced from the outside so the worst thing you could ever install would be say something like a power vent right because you're going to increase your air conditioning build or increase your heating bill you don't want to do that do you want this to be absolutely airtight and you want to wash the entire underside of your roof deck with air so you want continuous soffit vents you don't care about whether you have a ridge vent or mushroom Vance or guide the holes at the top are not as important at the highs of the holes in the bottom you want a lot of holes at the bottom and not so many holes at the top and then what do you want to do you want to like put a little wall in here and fill this with fluffy stuff pinks a pretty good color but I got news for you the color doesn't matter it could be other colors for life so you basically are building a bathtub right bathtub with walls on the side that you fill with stuff the reason you want the walls on the side is you don't want air to blow through the side of the bathtub right so you put a bathtub on the top of your house and fill it with fluffy stuff lots of holes and you know what works everywhere works in Tuktoyaktuk and Key West unbelievable the best value proposition of all right I mean you can put our sixty insulation in there for almost no extra cost from our thirty right nodding here you're in the fluffy business this would be a good thing right so how can we possibly screw it up well real easy let's put the heating system and cooling system up there what do you guys on crack what are you thinking this is unfreaking believable stupid the hottest place of all is going to be the Attic the coldest place of all is going to be the Attic so let's put stuff up there what the only thing up there should be nothing besides fluffy stuff and air right okay what's the big deal well because you can't make the ducts tight you know even if they're tight there five percent leakage right and they're typically twenty percent leakage then you get this huge negative pressure right because the air that leaks out of the ducts had to come from the house if radon was valuable you would mine it this way if you wanted to collect soil gas pesticides herbicides tremendous IDEs this is the best way to get stuff into your house you kidding me this is colossal estupid and what's the r-value on the docks nothing right nothing because this is madness this needs to be put inside if all we did was have the ductwork inside with an airtight ceiling vented attic with lots of fluffy stuff that is probably the most energy efficient thing that you could possibly do in construction in the United States unbelievable guess what it's not going to happen is it right it's unbelievably difficult to take this and put it in here people don't give space for it so this is by far the best technology we have this issue where is very difficult to convince the industry to do this to give you an idea of the penalty of just putting this into this it's about 25% 25% loss just to put the stuff up there unbelievably difficult what's the other thing that happens well we perforate the ceiling right let's put a thousand holes in it then we say well that's easy make every one of those holes airtight are you kidding me you kidding me yeah well you know write it on the specs the industry will do it just airtight hole airtight holes thank you I reached for that I begged for that see you know you're not allowed to ask questions until the end but laughter is appreciated okay all right the other problem again I I spared no expense at props when I first started in the business a long time ago before I went to university works with my daddies we're contractors and we get rows like this you could actually build this roof flat ceiling airtight and then what happened I married an architect and I get Rosa look like this the more complex the roof and the more penetrations and trays and coffers and all of that stuff it becomes unbelievably difficult to provide an air seal at the ceiling plane so the answer has been to move the insulation to the underside of the roof deck not because it's a better solution but because of all of the other bad decisions that we make to try to compensate for that you understand so the first best destiny is a vented attic with an airtight ceiling you go to unvented condition roos when the roof geometry is so complicated there's so many penetrations you don't have a choice when you cram the mechanical system up there and you have no choice those are penalties those are penalties those are not advantages are you with me on that and the problem is is that we do a lousy job of explaining it now if I've got any leaky ceiling not even venting will save you from something called ice damming because you've got so much heat coming out of the house if you have snow on the roof deck you're going to basically have the roof deck at above freezing temperature and if the outside temperature is below freezing and you have snow the snow will melt run down to the edge it'll freeze you'll get an ice dam this is a heavy if this falls on you you will feel it if it gets really big it will take a deck away one of the neat things about ice damming is that what happens is that the water melts and in the liquid phase it actually wicks up into the snow filled by capillarity so that the ice actually isn't directly in contact and frozen to the roof membrane or the roof shingles so you end up with a gap that the water runs down but it completely freezes here because there's no heat and so that's why it's called a dam and then it backs up so the critical area is right here it's not up here the other problem with air leakage from the inside is moisture and it accumulates on the coldest surface is basically the nails first and then the sheathing you don't get a lot of damage and accumulation on the top cords of the framing because they're only there one or two degrees warmer and that one or two degree temperature difference has a huge impact on the moisture distribution so you don't usually have a roof collapse structurally but if you walk on your sheathing you'll bust through it and it has the most most significant impact is on your shingles because the nail holding of the nails is lost so during wind events your shingles are lost so the most common tell is not a rotted roof but my shingles are blowing off because I've lost the ability for the nails or the fasteners to hold things Oh SB doesn't come that color new this is not the answer this is a guy with too much time on his hands warming up every nail smart old guys you'd basically make that critical area where the damn fold forms slippery so that the snow would slide off or the Dan would slide off this is kind of amusing because this is a school and the school boards heads would explode today you're going to say well what we want is to have deliberately let the snow slide off because you know if it fell on children that would be like horrible but if you're that stupid of course in Aspen which is the greenest town of all they melt the snow with electricity but the electricity is produced with PV panels but they ruin the look so they don't put the PV panels on the houses they put them in a field out of town and they lease them I don't make this stuff up this is what you know renewable technology does without adult supervision see the right way to do this is to have lots of insulation in your bathtub and then the vent and then you don't need the snowmelt you don't need the slippery thing you can do it by not doing stupid things but apparently stupid things are profitable for consultants so one of the alt one of the solutions to all of this is well it's not just membrane the whole roof let's put this fully a huge membrane on this well it doesn't address the real problem it addresses the water leakage out of the ice dam but it doesn't stop the ice dam from happening the way you stop the ice dam is you have an airtight sealing lots of insulation and lots of venting right nodding here would be whoo we're all on board okay this is a very easy to understand graph that was the so cynical comment it's not very easy to understand this is you know what you would get out of a government report this is the r-value of snow based on density the r-value snows about r1 to r2 per inch Canadians know this because we live in igloos and play hockey but apparently not very well so this is the r-value of snow why is that significant well if you have ten inches of snow on your roof that would be between r10 and r20 what does that do to the temperature of your roof deck this is not complicated I mean it warms it up right and so for years we've been hearing from the greenie wienies that look if you just have an r60 roof you can make it unvented in a cold climate because you don't have to vent it to control ice damming how many people heard that come on raise your hands even if you haven't just make me look good I'm having to beg for this this is just not alright what will happen is that even with an r60 roof if you have ten inches or more snow on the roof you're still going to get an ice dam because of the thermal resistance of the snow in other words at a high snow load area when the ground snow load is greater than 50 pounds of square foot your only option to control ice damming is to vent the roof even if the ceiling is airtight you can't put enough insulation in that roof to not to compensate for the thermal resistance of the snow that's just the way it is so even with an unvented roof you have to put a vented over roof over it to compensate for the thermal resistance of the snow blanket it can't be done any other way this is a this is in Vermont this is an r60 roof and this is a continuous ice dam what happened well because you clearly didn't read my book all right so what do I got going on here well okay this is perfect ice dam weather and the Sun is beating down on the siding here and it's about 20 degrees Fahrenheit outside and it's sunny what do you think the temperature of the siding is under those conditions okay you're not supposed to answer I know this thank you for not commenting you're allowed to laugh it's about 40 degrees to 50 degrees the darker the cladding the hotter the temperature and what do you think the temperature of the air is that's touching the 40 degree to 50 degree cladding it's hot and of course what happens is that that air moves up right into the soffits to cause the ice dam that the venting was supposed to prevent so there's got to be a catch well of course the mixing ratio right how much air from the wall compared to the free stream right all right this is your problem where we should the vent be located right here and if you're really smart you insulate the overhang so in high snow load areas like and ski here is on the top of mountains you always have your vent intake at your fascia you have to insulate the overhangs and you have to have a really high r-value and you have to vent the heck out of the darn roof all right this is my favorite place this is the lodge at the top of AK Ajax Aspen Mountain in Colorado and it's a LEED building which means it doesn't work dangerous snow slide area keep out they couldn't get in because all of the snow would slide off the roof they had there are 60 or 70 roof but it was invented and of course you got this big overhang and facing you know Southwest you get the Sun and so the only solution is hiring basically Australian ski bums to shovel the snow off the roof and the reason you hire Australians is because they'll do stuff rats won't - my best friend is Australian come on but of course this trash is the roof right and so what needed to be done is that they needed to vent the heck out of that roof and they needed to insulate the overhang right so insulation and air tightness and venting right okay so what do we got here I've got a unvented roof with a vented over roof with the fascia offset so that the air comes in and goes up here to yours well the ridge vent is covered with snow well snow is not an air barrier it's an air retarder slows it down but I got enough surface area yeah so if you're ever buried in an avalanche and you don't panic if you breathe slowly you will survive the problem is not panicking good luck with that strategy and then they they have to find you before you turn into a popsicle so you got those two things too worried about but according to a wolfy simulation it will probably work all right so the only reason this works and is the strategy that you would want to employ is if you put the mechanicals up there and there's no practical way of sealing the roof plane maybe with me there is this is not the best destiny but it's a viable strategy when you have complexity so for people to say you can't do this the answer is well no there there's always going to be some place we're going to have to do this this is not where I started with but there you go but if you do this in the snow load area you still have to put a vent at over it's not going to work for you well how did the first unvented ruse work well we simply would take successfully performing flat compact commercial roofs and sloped them and the biggest thing was this compact roof was the air tightness here you absolutely need to have an airtight ceiling plane of course that's the first thing that gets valued engineered out during commercial construction right they have the fluted metal deck and they throw a bit of Isis and yaw rate down on the top of that and the only thing that saved us was a black membrane because the black membrane would get so hot it would bake the moisture back down and then what happened those the energy efficient lunatics made us put white membranes down what were they thinking well they saved a lot of energy but you didn't get the reverse Drive and what that meant is that you had to have an air barrier so we basically moved a cold climate problem from Ottawa to Atlanta Wow we still have this argument well we can't have we can't we can't afford it I said well looky she'll just get two layers and install the joints horizontally and vertically offset and you're done you know your insulation can be your air tightness layer oh you're a legend yeah I know who told me that old guys yeah had it figured out so you know young Joe when I was in my thirties he you should probably put your insulation in two layers in stagger the joints and maybe put some tar paper between the two layers I didn't know until I got older that that was like wow you know these guys know stuff and and you know Simon now that I'm old I am always bragging about the old guys so let's slope it put down a fully adhered membrane a couple of layers of insulation with the joints offset horizontally and vertically another layer of plywood or OSB screw it down another membrane shingles this is a phenomenal unvented compact roof is it as energy efficient as a vintage roof no not even close all right not to scale okay this is complicated same our value here and here what's the difference in surface area about 1/3 30% more so all other things being equal an unvented roof with the same r-value is going to be 30 percent more inefficient nodding here would it does not even cloaks right the only reason we do this is because leaky ducts have to have more heat loss than 30% to win right all right the other thing is that all things are not always equal where people win is that they do allow the job of air sealing this and they do a great job of air sealing this so the only way that you can win this argument thermally is to say that this unvented approach leads for a lower air change in the building because my building construction is tighter and I am comparing it against duct trick located in an attic that is with the duct rate leaky it's the only way you can win that but that happens all the time so I'm going to say maybe five ten percent of the time it makes sense because of that but it's not the best destiny it's not the preferred then we have architects who like the vaulted look okay I get it and it's beautiful but don't confuse beauty with efficiency the best is a beautiful thing that's efficient but I get a lot of beauty that's not very efficient but I live with it why I'm old I love poetry like beautiful things I'm going to give up BTUs for beauty and he to the wake and when you get as old as me you're give up energy for beauty as beauty thing is a big deal in a snow load area you put the vented roof over the top of the unvented roof to make it work what's snow well people who live in a high snow load area usually know it they know they get a lot of snow if you don't know 50 pounds of square foot ground snow load you got a vent and it would be nice to have the inlet at the fascia and insulate the overhang this is a for those of you who are American high school graduates have not seen this before this is a map of the United States Eady it shows the ground snow load all right I did a lot of these and back when I was poor and had to work for a living these are post-and-beam structures and the post-and-beam structures were done with basically compact roofs but we found that we had ice dams unless we put a vented over roof and so there is our our assembly the air barrier the insulation learned a lot but apparently not enough to keep me from embarrassing myself as I got older did swimming pools all the structures to the inside fabulous this is uh was the world headquarters for building science corporation this is my barn and I wrapped the whole thing in a perfect air barrier to expose all of the timbers and stuff to the inside this is an in Boston then I put eight inches of foam on the outside I'm making the world's largest Canadian beer cooler but it's located in Boston here is my big mistake 10 inches on the roof and I should have put it up in two layers or three layers with the joints offset horizontally and vertically but the most dangerous time of your career is in your late 30s and early 40s that's when you actually think you know stuff see when you're younger you're convinced you know stuff but nobody will let you do anything because they know you're an idiot right when you get into your late 40s and 50s you're saying I can't believe I survived the stupidity I did in the late 30s and 40s right so I didn't have any adult supervision and and and oh my god so the very first winter and so I'm like I'm aghast right so I'm on the sidewalk I'm bashing my head against like this and I'm hoping nobody sees this and one of my neighbors who I haven't met because this is the first winter and haven't you know we're kind of people don't really talk to them each other in New England says old guy big tall old guy walking his dog stops and he looks at this and he says you know if you'd put that insulation up in two layers with this with the joist offset horizontally vertically you wouldn't have this three dimensional airflow Network happening and I looked at him and I I said who are you he says I'm your neighbor my name is Carl cash yeah Carl cash is probably the foremost roofing expert in the world he passed away recently and and anyway so for the next 15 years mr. cash and his mangy dog now would walk by and stop shake his head and walk away and my private parts would get sucked up into my body and shrink and shrivel so nothing is more embarrassing than screwing up your own house right so why do I talk about it well I finally got around to fixing and well it's in them it's an important lesson I did have an air barrier but it did show that we've got network network flow in the composite that's a big deal I mean you know I never will forget this right you know is one of those lessons that man and I only talk about it now because I could afford to fix it so da ha ha ha but so next time I saw it I knew it instantly right and so how come you know these things well I just know these things I don't tell him that I was like an idiot but usually if you live long enough and you survive the eita see you're you know kind of smart it's the time between you get there that is the problem so this is Juneau Alaska and it has probably we probably had the biggest sip structural insulated panel failure in the industry history about 400 house 350 houses rotted the roofs and we hang I was in the neighborhood and I knew it right away the tell was mushrooms growing out of the shingles we call this the Wolfgang Puck effect see he runs a restaurant pizza and I have to explain these jokes it's not going to go fast so the rot follows the panel joints Ridge and the joints and amazingly enough we call it Ridge rot because the moisture all ends up at the ridge because of hydric buoyancy and thermal buoyancy yes moisture Latin air is less dense than regular air yeah whatever so this is not a is not a vapor barrier problem this is an air leakage problem at the joints and you know because these these panels slide together you know just perfectly you know they're 30 feet long and you know you just slide together perfectly you don't need a sledgehammer or a come-along and bad language we did our first sip roof with my dad I learned stuff about my mom I had no idea anyway it's impossible to get your air seal at the bottom it's easy to get the air seal at the top and you've got this convective looping where you've coupled basically the joint to the interior space I mean and the instructions are comical you know that panel you know leaned over and put a continuous bead of sealant unbroken and it's always done on under warm dry dust-free conditions and Bubba who's doing this is always in a good mood he doesn't listen to country in western music well yeah if you play a country and western song backwards you get your dog back your girl back your truck back your job back and you never want to install this on a Monday after a NASCAR race so these two panels are coming together right here here's your giant moisture comes up hits the roofing felt changes from a vapor to a liquid and this wycked away 15 inches by capillarity whoo I use a big word there he's the Russian judge six point five so here's the splines there's an air gap here and an air gap here on either side of the upper spline that's matched by an air gap I've paired with another air gap on the lower spline and you know somewhere between the two these two these four micro ducts connect with one another you've got this wonderful cycle happening yeah I've got these experts they're all at $400 an hour saying yep you're screwed pretty much okay so I go to Green Bay this is Molson muscle this is the inverse Nike sign don't do it and so the the tell with sip rooves that we're failing is again shingle blow-off right that's the first thing that you notice rarely do you get enough condensation dripping through for stains in other words this stuff is happening you but you don't know right it's it's one of those who something bad is happening but I can't tell so you go up there and it's kind of neat it's all happening at the ridge ah all happening at the ridge hmm hold that thought well continuous unbroken seal here good luck trying to get it here try to get a continuous seal here we call that faith-based air sealing it's part of the new program it's real easier but you know this needs to be here so you got to have a continuous tape there and of course everywhere the panel is sitting on some side of structural member how do you get that continuity it's to the point where I don't think it's possible and I love sips I mean you know not like my children I like my son better than my dot and I don't I'd like them both equally the point is is that for sip rooms we always want a vented over roof over the SIP because I have I don't have the confidence in having the trades to be able to do that fastidious a job for air sealing and a vented assembly gives you that forgiveness even with an unvented compact roof I just and you know what do these put over there put over community areas with you know exercise things and spas and pools and the bigger and more complicated the assembly the more likely you're going to get something magical like this and you can't you got to put that safety factor in of course you explain to them is it but this then they put down a fully adhered membranes there's no has to be vapor open right not nodding here would ya okay got it well we fixed a lot of them by over roofing right by elevating the temperature of the condensing surface by putting enough rigid insulation on the top right nodding here but you had only a 3 to 4 3 to 5 year window right before it completely rotted right and then what do you do then you have to reach down inside and say how much of this can I keep and how much do I have to rip out well yeah safety factor oh you know it's ok you get the idea well one of the things that we did that worked really well was we said let's strip away the rotted part there's usually only a foot to a foot and a half at the ridge and then cover it with a vapor open membrane and then put a vented ridge cap over it works because where does all the moisture end up at the ridge and I'm thinking oh I could maybe do something with this sometime maybe I should like file that away huh see some of the possibilities oh guys make pink fluffy stuff ok all that thought so what you need is a graduate student that you don't pay you guys use interns we use graduate students this is the smartest graduate student I ever met in fact actually he's an employee he's now a professor in Texas phenomenal guy and we're doing a roof and we're creating a diffusion vent and I said that it was twice as wide as it needed to be and he did all these calculations and he's smarter than me and he says well how could you possibly just go there and say in two seconds that it's twice as big as it needs to be and my answer is well I'm old I know these things how bill the law and I says well the roof tells you the rod is only eight inches so I only need an eight inch vent so you need to get out of the lab you don't go to the problem I don't trust your analysis you might be the smartest person in the world but not to me now if you do go to the field and then you do the analysis then you crush everybody there's no defense except yeah in Indiana and that doesn't work very well except in code hearings anyway turned out that this event was twice as y as it is needed to be and it's not a technology that works for hips but what we did try to do is we filled it with cellulose and we're trying to get it to be a dehumidifier a solar dehumidification system where the idea is we would draw air moisture from the house would be absorbed in the cellulose then with what we call the ping-pong effect would end up at the ridge in vent and it works it just says it doesn't suck out enough moisture to make enough of an impact in the house in other words yeah that's absolutely true but it doesn't give enough of a dehumidification effect to counteract the moisture load the air leakage and everything else but what it does do is it means that the sheathing is unbelievably freakin dry and there are palm trees in this picture or somewhere so that gives you a whoo hold that slot up go to Lexington why home of bourbon it's like a shrine these guys are making these panels they're called nail base let's throw them down on the top of the roof the problem is is that there's no air tightness at the bottom and of course there's never any joints between the panel's I'm using a biomechanical error sensing device if you lick your hand it's good to a Pascal this is not an ASTM test the ast M stands for another stupid test method this is very practical anyway so you've got this three dimensional airflow Network because they needed an air barrier we're on the deck and then of course in the auditorium you want to know how come there's more of a problem in the auditorium that's because they perforated the deck for acoustical reasons yeah so yep air tightness in Kentucky so there was the solution air barrier two layers of rigid insulation with the joints you got it I know this I just can't tell well I did tell you well alright so I could put fluffy stuff up here and I could put rigid insulation on the top of this to warm up the condensing surface and if you think about it that makes sense because I'm just taking a wall with insulating sheathing and putting it on the slope right and the amount of insulation I have to put up there is going to depend on the climate location in the interior moisture load if I have an indoor pool you don't want any fluffy stuff on the inside you want everything on the outside right a low moisture load like you know thirty thirty five percent RH or a house this this works or you can put the insulation here as your air barrier and have your vented space this is a phenomenal assembly what's neat is that you don't have to be perfect you need to be good you have to be perfect perfect is hard now we did about a hundred thousand roofs in Las Vegas with fiberglass bats netted cellulose blown fiberglass with no air space and no air barrier down here for this was OSB with tar paper and tar paper is not a vapor barrier and then we had batten strips with tile so I've got a ventilated cladding if you stand that up it's like a wall that has an air gap behind the cladding huh what do you think you might be able to work with this and we know we got all these you know probably over a hundred thousand since 1995 this led to the code change people ask me well how come it only works for tolerance well not for asphalt shingles because the Asheville shingles do what they don't they don't breathe because they're got you with me on this okay I you know I'm people like they're discriminating against household must be a fire thing no it's not so the people that really picked up on it we're the silos people I don't know why you guys didn't and yeah maybe you needed a better management team that was 15 years ago come on relax get back in the game ah wrong color though I'm sorry why did I use this color well they gave it to me you're stunned but it works then we go to Phoenix and you've got a black man brain and they just shoved it up in there and it work just fine why because it was a black membrane remember and the moment they change these to white they got drywall cracking on the interior walls and I said I got the call I says well he said how come the drywall is cracking whether you change the color of the roof membrane that's when they threw me out you're like a lunatic how could changing the color of the roof membrane cause drywall to crack well making the membrane white top cords of the trusses got wetter and expanded we got trust fries huh then they opened it up in there they saw a little bit of mold oh my god mold mold are all gonna die die oh you know it you know take a valium calm down relax so how to fix this well it was easy put rigid insulation on the top right with me on that well so we just put down that new roof membrane and that's when folks started spraying foam on the underside because it was cheaper to fix these which baffled me must to move people out take the gypsum board off of the ceiling spray a couple of inches of foam and put the gypsum the fiberglass back and and put gypsum board up I mean to me I would have like done it from the top right that seemed logical and I said well yeah this will work but really and so you know that's where it started fixing because they for whatever reason they didn't go with this they went with this and so then they said well you know what kind of foam can I use well low density or high density well the high density stuff you could use everywhere with the low density stuff is a sponge right absorbs moisture and so you need a vapor retarder associated with it and you need a means of removing the moisture from that attic space otherwise it's going to accumulate over time right so that's where the code provisions came from so you know this low-density half pound density foam is a phenomenal product if you have an air change in the attic that's coupled to air the house now for most of the buildings this works just fine because what do we have up in those attics well if you have leaky ducts leaky ducts by virtue of being leaky and a leaky ceiling means you have what a and air change but if you put in tight ducts and a tight ceiling you're going to have a problem because the moisture is going to do what it's going to stay there so for these unvented attics to work and by the way they do work well is they have to be coupled to the conditioned space or they won't work everybody with me on this now so you can't say on vented rooms don't work in fact I have a problem with the term that's why I'm using the term conditioned attic now many people have heard of unvented crawlspaces right the same problem you can't have an under crawlspace you have to have a condition crawlspace and in you know you all know that there is a place for conditioned crawl spaces just like this is a place for conditioned attics but they're not the most energy-efficient option with a clean sheet of paper but they might be the only strategy that you have on a retrofit situation or in a complex new design right so it's a design choice but if you don't do the coupling big problem so all right show you all of this stuff this is an experiment we did 2004 and apparently we didn't publicize it very well we basically showed there is not reverse Drive through the roofing system from the top side right you don't get reverse Drive well how do we know well we did it the old-fashioned way let's build a whole bunch of stuff and see now what this meant was that when we did the first code change language for unvented Roos which should have been called conditioned Rose in Florida the Florida Building Code in 2001 has a requirement for a vapor barrier membrane an impermeable roofing membrane that's because we were suspicious we were nervous so we put in the safety factor we didn't meant for your studying and to say it wasn't a problem which is why in the IRC language which I wrote and got passed in 2006 there isn't a requirement for a vapor impermeable membrane I thought the matter would be dead right I thought well you know okay we did the work and we got the code change so but we didn't publish and didn't say don't it's okay relax take a valium it's not happening so for the last two years is people are obsessing over this and well stearic you never published a peer-reviewed paper yeah we had the aunt I'm an engineer we had the answer we moved on right I mean yo we fixed the code I'm sorry that I didn't have a bunch of worthless academics looking over my show saying it was okay okay so this works only if it's coupled and it's vented by diffusion right if you want to use spray foam in there the open cell has to be coupled to the inside space has to be so we started experimenting and we said we'll look why can't I put cedar breather under asphalt shingles you know and I mean like you know the brillo pad or maybe I could convince a single manufacturer you wouldn't happen to know one would you two maybe give me a bumpy shingle so created this experiment in Chicago where we're looking at all these options our control as a standard roof and a completely trashed unvented roof with all kinds of different options and we're heating and humidifying and we're figuring out what's going on so this is our test structure in Chicago we got away with it because I know the building official there he said Joe if this doesn't work the Ranger is not going to like this so let's have an opening and invite the mayor good idea this is how it works so we've got a project in Houston and one in Orlando the idea is that we're basically leaving a ridge slot because all of the moisture ends up where at the ridge and we're putting a vapor permeable membrane and putting cedar breather in a ridge cap and we're doing this with cellulose and fiberglass because I believe that you can use netid cellulose netted fiberglass fiberglass bats sprayed fiberglass and in conditioned attic space just like low density foam except now we're going to use the ping pong effect and move the moisture out through the ridge I think that's a huge opportunity because it reduces costs and reduces the risk of the with spray foam and so just so that you appreciate how we got to this we got to this with failure not success I'm convinced after 30 years that failure teaches more than success does there is an old joke in civil engineering structural engineering you should never hire an engineer who hasn't had at least one bridge fall down because they're over designing but you should never hire one that has to fall down because they haven't learned and so I think there's no substitute for investigating failures in the field and in fact creating controlled failures to see to push the technology to see what it takes to fail and use the real-world boundary conditions to tune your models in your experimental work and then you can go places that are magic with that thank you very much it was a real pleasure doing the presentation if any of you have any questions or comments or follow-up please contact us at building science.com and there's a information and questions section there and we'll be happy to get back to you Oh

Channel: Owens Corning

Views: 1,122,499

Keywords: Building Science, Dr. Joseph Lstiburek, Vent Roof Assemblies, Vent, Unvented, Jospeh Lstiburek, Building Physics, Barrier, Surface Area, Owens Corning, insulation, Pink, Fiberglass

Id: Ld8pzIu45F8

Length: 53min 10sec (3190 seconds)

Published: Thu Feb 13 2014