Joseph Lstiburek *(highlighting is mine) “Attics or roofs can be designed and constructed to be either vented or unvented in any hygrothermal zone (Moisture/Heat zone). The choice of venting or not venting is a design and construction choice not a requirement determined by the physics or by the building code. The model building codes allow both vented and unvented roof assemblies. The applicable physics impacts the design of attic or roof systems as does the applicable building code but neither limit the choice.” Joseph Lstiburek *(highlighting is mine) Before we get into attic ventilation it is important to keep in mind, this information from Joseph Lstiburek. (read slide) While the “physics” of all this does not change, different climates can, and will, make a huge difference in how the physics have to be managed. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

So you live where it is Hot and Humid? WHERE IS THE DEW POINT? (A bit like “Where’s Waldo,” it can surprise you where it is.) Problems with Venting It “can” work, but you better keep your HVAC equipment and ducts out of the attic. Hot roof solution Shorter shingle life? Use of non-air sealing types of insulation Right off, I want to stress this presentation is largely focused on cold to mixed climates and if you live where it is hot and humid, I cannot help you as much as I would like to think I can. I probably understand enough about hot and humid climates to create more issues than I would solve—but I am starting to make sense of it. While venting attics in hot/humid climates “can” work, it is often made problematic due to the insistence on putting HVAC equipment (cooling equipment) in the attic. It is very easy for the cold ductwork, HVAC equipment and drywall surfaces to get below the dew point leading to condensation problems in the roof structure. Compound this issue with the ductwork actually leaking in the space, and much larger areas could become below the dew point. If it is REALLY hot and humid, the dew point will be reached on much “warmer” surfaces than one might think. Certainly, 58° F ductwork will fit the bill. If a typical Orlando, Florida temperature/humidity in the summer is 91/58, what is the dew point? The dew point is 74° F. So surfaces at and below this temperature can start to form condensation. How about Mississippi with a temp of 74°F and 99% humidity? The dew point would be 74°F. This should make it pretty clear as to how risky it is to be putting the HVAC equipment essentially outside the building envelope---insulated to the required R-8 or not. Some think the solution is to insulate the roof plane so that all the cooling equipment is inside the thermal envelope. This certainly makes some sense, but it is not without its risks and problems as well. Keep in mind as you insulate the sloped roof, you are at the same time increasing the overall volume of conditioned space---perhaps as much as another 50% of a floor level (essentially turning a 2 story 3000 square foot house into perhaps a 3500 square foot house---a15% increase in heating and cooling). There is some evidence that this can shorten shingle life “slightly”---but not as much as color does. Some, including me, futilely argue for not putting the HVAC stuff up there to begin with. It is a moot point as long as non-air sealing types of insulation (like white fluffy) are used to insulate because the wet air will still find its way to the cold drywall under the insulation. Venting of attics in hot and humid climates “can” work, but you better keep the HVAC equipment out of the attic and use sufficient air-sealing insulation. In the South one will not likely have ice dams, but one can have condensation of cold ductwork in the attic. You will even see condensation form on the uninsulated condensate drain lines. They are cold and the air is wet---hence dew point is reached and condensation happens. The more humid the area you live in the more likely condensation will be an issue. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Photo Courtesy Gary Smith, SafeHome Inspections, Mississippi The light grey areas on the plenum are areas of condensation where the cold metal is condensing moisture out of this humid Mississippi attic. Photo Courtesy Gary Smith, SafeHome Inspections, Mississippi Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Photo Courtesy Gary Smith, SafeHome Inspections, Mississippi This IR image shows how much colder the plenum is in the areas of condensation, and is visible to IR due to evaporative cooling. Photo Courtesy Gary Smith, SafeHome Inspections, Mississippi Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Pretty much everything you need to know about attic ventilation can be summed up in two words: Air Sealing! Pretty much everything you need to know about attic ventilation can be summed up in two words: Air Sealing While radiational cooling can be, and is, a factor in adverse moisture conditions in attics, by far the most important cause of excess moisture in attics and roof structures is conditioned air finding its way into these spaces. This of course assumes there are no roof leaks. Just like moisture conditions created by radiational cooling, other excessive moisture issues in ventilated attics cannot be fixed with more ventilation. This of course assumes there is some amount of ventilation at all. To repeat: Excess moisture in a ventilated attic cannot be fixed with more ventilation. Ventilation being THE answer is trumpeted by home inspectors all over the country and it is time to get on board with the fact that it is not the answer. The mold industry perhaps trumpets this misinformation more than home inspectors. The following is from a popular mold site: “The most common attic humidity level buildup is due to lack of proper ventilation.” They go on to clarify that this includes improperly terminated exhaust fans and even roof leaks, but it is their “solution” that is unacceptable: to increase ventilation! This next point is so important it deserves its own slide: Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

If you think additional venting is “the answer,” you will be wrong, WAY more often than if you assume it is not the answer. Read slide Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

What IS “Air Sealing?” Air sealing is simply using whatever means is practical to stop or slow the movement of air from one space to another. Vapor retarder (paints, plastic sheets, some types of insulation) Caulk Paints Spray foam House wrap Drywall Liquid WRB Sheathing (Plywood/OSB/Foam Board/Etc) Tape Weather-stripping Insulation Etc Read slide Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Would you ever recommend fixing a roof leak by adding ventilation? I hope not. I think most of us would recommend the roof be fixed. So why do we think we can fix a moisture issue coming from the interior by increasing ventilation? (As a side note, one could actually make a roof leak worse by putting the attic under negative pressure with increased ventilation—especially mechanical ventilation.) Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

EVERYBODY knows inadequate ventilation is the cause of everything! But what about ventilation? Myth #3 EVERYBODY knows inadequate ventilation is the cause of everything! Cold Climate Hot Climate Mixed Climate Myth #3 EVERYBODY knows inadequate ventilation is the cause of everything! What is the purpose of ventilation and what does “perfect” ventilation look like? The answer to this question, if there is an answer, will depend on your climate. In a cold climate, the primary purpose of ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow and to vent minor amounts of moisture that moves from the conditioned living space to the attic. In a hot climate, the primary purpose of ventilation is to expel solar-heated hot air from the attic or roof to reduce the building’s cooling load and to relieve the strain on air-conditioning systems. There is considerable evidence that not only is this a bad idea, it can make things worse. Achieving those goals may be easier to achieve in other ways. In a mixed climate, ventilation serves either role, depending on the season. It is interesting to note that in a mixed climate, the errors and omissions of one season can often be remedied by another season. … Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

So what about Ice Dams? Or maybe “damns” is more appropriate. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Myth #4: Everyone knows ice dams can be fixed with more ventilation ** This is only partially a myth. While some amount of ventilation is necessary to prevent ice dams, too much ventilation will certainly make them worse as will too little ventilation. This talk is not about ice dams specifically but some of this information will point to why ice dams are happening---and even point toward their solutions. In a roof with no venting---otherwise known as a hot roof---if there is not enough insulation and air sealing to stop heat flow sufficiently, you can still get ice dams. If you live in some uninhabitable place like Minnesota or Syracuse, that might mean R-60 insulation---but not just any insulation---insulation that is also a good air barrier. It is also important this insulation be “continuous” with no thermal bridging. This is very difficult to do at reasonable cost in conventionally framed houses. It would be cheaper to do a double roof with an air space above the insulation. Air moving through that space will sufficiently sweep away any minor heat that is lost to the space from the interior---or gained to the space from the exterior---keeping the space close enough to the outdoor temperature. We essentially want to do this same thing with attics---keep the air temp similar to the outdoor temperature. Again we need a good thermal barrier that is continuous and a good air barrier as well. In VERY cold climates a good vapor barrier is also important. If we install ductwork in the attic, even if it is properly insulated to modern requirements (not nearly enough in my opinion), they can still give off enough heat to allow for ice damming in cold climates. Fiberglass in its many forms simply cannot do this.

Air Sealing has to happen first Hey! I have trained him to walk backwards! Modest amounts of ventilation can achieve these goals once good insulating and air sealing has been accomplished. But we must not get the cart before the horse. AIR SEALING HAS TO HAPPEN FIRST Fixing older homes is much more problematic and WELL beyond what we can get into today. There are a few other modes of heating attic structures that can result in ice dams. 1. Heating that is caused by solar loading of the roof surface itself. 2. Solar loading of the walls under soffits where the heated air pushes its way into the attic. These are both more unusual ways to create ice dams--but they can happen. These are less likely because the input is not 24/7. Better thinking about house orientation, placement of soffit vents, size of overhangs, and proper venting in general play a part in sorting out ice damming from these modes. Air Sealing has to happen first Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

This is “modern” construction---2006 build This is “modern” construction---2006 build. The roof structure where the ice damming is occurring is a 2x10 vaulted ceiling with the entire roof structure insulated with Icynene. It is a Hot Roof installation---no venting---no space to vent. Can you see the ice and water stains coming out from behind the siding? Looks like we are going to need a bigger kick-out flashing  Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Solid Wood is not sufficient to prevent ice dams The 9-1/4 inches of Icynene ought to be about R-40+, so why has it failed? It has failed because all the wood double top plates and the wood rafters themselves are only about R-6 and R-10 respectively. Together they allow enough heat to move to cold to melt the snow on the roof where it then re-freezes at the overhang. In a 20 foot long vaulted roof, with 2x10 rafters, 16” on center, 24 inches of the length of the roof will be at R-10. (16 rafters x 1-1/2”) Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Picture courtesy of Jim Quarello, JRV Home Inspection Services, Llc. This is a serious problem that will not be easily fixed. This is ice damming on a house in Connecticut. Picture courtesy of Jim Quarello, JRV Home Inspection Services, Llc. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Picture courtesy of Don Hester, NCW Home Inspections, Llc. Note the snow cover is less over the conditioned space and heavy at the overhangs on this house in Eastern Washington State. This is a clear example of heat loss from the interior melting the snow and then re-freezing when it gets to the overhang. Picture courtesy of Don Hester, NCW Home Inspections, Llc. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

50/50 or 60/40? 1/150 or 1/300? Lower Upper OK, now we have to get some technical stuff out of the way. We all likely grew up with the old 50/50 relationship. I know this is the way it is taught in many home inspection training courses and continuing education---and even seems “politically correct.” 50% of the ventilation up high and 50% down low is also supported by the building codes. These numbers never really had any hard science behind them but date back to the early 1940’s. They remained the standard until Joseph Lstiburek came up with some numbers based on actual testing. That said, the percentages in most cases will not create problems. In actual practice, all the house needs is closer to a 60/40 relationship. 60% low and 40% high. These percentages, are adequate to maintain lower attic temperatures, keep the roof cool, and to flush the very minor amounts of moisture that may still find its way into the attic. Attics can be VERY forgiving if very little moisture and heat is finding its way into the attic from the interior. These numbers in my experience can vary greatly if proper air sealing is done and depending on where the house lives. Best practice is to not let the top ventilation amount become greater than the low level ventilation. So these numbers are “practical” numbers that may or may not mean very much in actual practice. The codes do not make appreciable distinction between amounts or percentages of ventilation based on climate (with minor changes in percentages for VERY cold climates and whether there are vapor barriers or not) and I tend to agree with this, the principles pretty much work for all climates. This information is contrary to snake oil salesmen that want to sell power vents, but we will discuss that in a bit. But, we have to start somewhere, and it has been shown, if you vent to these standards bad things are less likely to happen. What makes this seemingly difficult is that no ventilation AT ALL can also work. Good ventilation results in a “slightly” pressurized attic. Write that down. Slight pressurization discourages air infiltration from the heated space that would be caused when the attic is depressurized, as when there is too much ventilation—but namely too much upper ventilation. This depressurization gets even worse when we add mechanical ventilation. A Mechanical ventilator, to stay “neutral” and prevent depressurizing the attic, needs approximately 1 sq ft of net free intake per 300 cfm. So a very small 1000 cfm unit “might” have enough square feet of intake with standard soffit vents in newer construction, but in older construction or with much larger units, there likely would not be enough intake. There should be 1 square foot of vents for every 150 square feet of attic except if you install a vapor retarder in climate zones 6, 7 & 8, or you provide no more than 40% of vents up high. Raise your hand if you know what climate zone you live in. (Maritime Zone 4 for the NW) If you raised your hand that is awesome. If you did not raise your hand, how can you know how best to assess attic conditions or know what recommendations to make to your client? A 1500 square foot attic would need 5 square feet (720 sq inches) of vent with 3 square feet (432 sq inches) low and 2 square feet (288 sq inches) high. How many square inches is the average roof box vent? These calculations are based on NFA or “Net Free Area” of the vent. A common box vent with a 9” diameter hole might only have 61 actual square inches of Net Free Area instead of about 64 square inches. 288 / 61 = 4-3/4 or 5 vents up high for the 1500 square foot house. Many standard vents range from 40 to 60 square inches, so using 50 as a median you can get a quick glimpse into how much upper venting there is. You have to wonder how many builders actually do the calculations. I see little evidence they do. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Myth #5: The more ventilation the better. Myth #5

Too much is never enough! Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

What the 2015 IRC says: R806.2 Minimum vent area. The minimum net free ventilating area shall be 1/150 of the area of the vented space. Exception: The minimum net free ventilation area shall be 1/300 of the vented space provided one or more of the following conditions are met: Ruh Roh, here comes the “CODE.” Don’t be afraid of the code. If you put an “s” on the end it is no longer a four letter word. It is the worst house we are legally allowed to build. The more you know about the codes the better you will be able to advise your client. In some cases it might mean you would be able to give them any advice at all. Contrary to popular opinion, it is my opinion we are code inspectors—we just have no code enforcement powers, and it is not all we are---we can do even more than what code requires. Regarding roof ventilation, the model codes are more wanting than perhaps anywhere else. The amounts of ventilation are entirely applicable to cold and moderate climates and are of limited value in hot humid climates. Do not expect them to change before the 2018 cycle. You may be able to successfully argue with your local authorities to waive these requirements if you can sell them on your own unvented system. You can anticipate problems with your attics if you vent to required standards and you have HVAC components in the attic and/or have loose fill fiberglass or fiberglass batt insulation in your attic. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

This presentation is mostly geared toward colder and mixed climates 1. In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling. 2. Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. This presentation is mostly geared toward colder and mixed climates This section gets a bit closer to Lstiburek’s recommendation of 40 upper and 60 lower and would be an option to use if you are in climate zones 6, 7 or 8. This is also another thing that is likely to help us if we are having a problem with Night Sky Radiational Cooling, as we are not “encouraging” the sucking of cold wet air into the attic. We can begin to see why we do not want to “guarantee” excessive ventilation with a power ventilator. What is painfully absent---is any mention of anything about zones 1, 2 or 3. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

These pyramid roofs can be difficult to vent according to industry “guidelines.” Lets forget for a moment that these vents may or may not pose problems with where air will “actually” flow. We will go into that a bit later. 8 vents times 50 sq inches equals 400 square inches, so by the “calculations” you can quickly see this 1400 square foot attic is “close” when using the 1/150 rule, but over when using 1/300 rule. How is an inspector to know? We can’t. All we can do is look for signs of issues in the attic. If it is a brand new house, we might want to mention that with no “history,” how well the house is venting could not be determined. Use it as a selling point to get you back for the one year warranty inspection. How many of you calculate the “actual” square feet of Soffit Vents or Roof Vents (Gable, Box, Ridge)? THERE ARE SO MANY QUESTIONS! There is: Bird-blocking: Are there vents in every bay? Or every other bay? Or just one or two on the whole side? Are they 3 hole vents? 2 hole vents? Screen vents that take up the whole bay? You might have Continuous soffit vents---not to mention a gazillion other types of soffit vents, such as: Rectangular soffit vents Holes or slots in vinyl or cement-board or aluminum Core-a-vent on the low roof instead of the soffits Box vents on low roof instead of soffits Round louvered vents On the roof itself we can have: Box vents, and many different sizes of box vents, Ridge vents---choose from several different types Gable vents---but also ridge, box and soffit vents may be present as well Vents up high Vents down low Configuration issues: Are multiple “systems” installed? Do different types of vents conflict with each other, changing expected flow patterns? Are there power vents mucking up the equation? Are there whole house exhaust fans mucking up the equation? ALL of these vents will have different Net Free Areas that you would have to know. On top of all these considerations, what happens to our calculations ten years later when the openings are all clogged with lint? Or if there is a vapor barrier on the ceiling? What does all this mean? Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

IT IS COMPLICATED! It is complicated! Since the primary functions of ventilation is heat reduction and keeping the roof cool, isn’t THAT what we should be figuring out? For a long time we have seen moisture issues in the attic as being related to ventilation, and we have a hard time letting the myth go. So unless you are inspecting the attic in the summer, and the roof is in full sun, how can we assess whether the ventilation is working to keep the attic cooler? Unless we are inspecting the attic in the dead of winter, and the roof is in either full sun or no sun at all, how can we assess whether the ventilation is working to keep the attic close to the same as the outdoor temperature to reduce the chance of ice dams? We probably can’t. The chances you will have ideal conditions seasonally, or at the right time of day, are VERY small. But generally speaking, if there are a bunch of vents and they are not blocked or they are not compromised by having multiple systems installed--the house will likely be fine. I would say this may be a much bigger issue if you were living in the South. In Seattle, keeping attic temperatures similar to outdoor temperatures in the summer is not too difficult at all. That might not be the case in Arizona. If we take the worse case scenario, as would be represented by a “hot roof” where there is no ventilation, if that is OK for the roof structure and shingles, I suspect whatever temp the attic builds up to is moot. I hear stories of roofs in the South being ruined from overheating---but I have yet to see the hard evidence. Where it does become a factor is where insulation is not sufficient to decrease cooling loads as the hot attic temps seek out the cooler indoor temps. Heat always moves from warmer to cooler remember. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

Myth #6: Attic sheathing temperature, on a sunny day, will be similar to attic air temperature. Myth #6 Attic sheathing temperature, on a sunny day, will be similar to attic air temperature. Not even close typically. Routinely I see inspectors post pictures of attic temps where they are shooting surface temps of wood structures inside the attic. This will not be the same as the attic air temperature. Use a thermometer---don’t use either an IR camera or an IR thermometer. There can be a huge difference. However if the venting is “perfect” or even “OK,” and there are signs of moisture issues, we have to know what to tell our clients. So it gets back once again to being a “visual inspection.” We need to know what we are looking at and what it means.

Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

This represents a roughly 40 degree difference between sheathing temp and air temp. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc