Until recently, building codes required that insulated sloped roofs include ventilation channels directly under the roof sheathing. As building scientist Bill Rose has shown, code requirements for roof venting were never based on research or scientific principles.
Because of their unscientific origins, code requirements for venting roofs are often misunderstood. During the summer, roof ventilation does not significantly lower the temperature of asphalt shingles or other types of roofing. While roof ventilation can lower the risk of ice damming, it's essential for builders to limit the flow of heat into roof ventilation channels by including one or more ceiling air barriers and by installing thick insulation, so that as little heat as possible escapes from the home. While roof ventilation can help dry out damp roof sheathing, it's essential to limit the flow of water vapor escaping from the home so that the roof sheathing never gets damp in the first place.
In the absence of an airtight ceiling, roof ventilation can do more harm than good, since air movement in rafter bays can encourage indoor air to leak through ceiling cracks.
Ventilation channels are created by installing a material that can maintain a separation (an air gap) between the insulation and the roof sheathing. The first vent baffles to hit the market — the classic Proper-Vent of the 1970s and ’80s — were inexpensive, flimsy items made of thin polystyrene.
Eventually, manufacturers began offering stiffer alternatives that are better able to resist the pressures of dense-packed insulation. Some builders aren’t satisfied with commercially available vent baffles, so they make their own site-built baffles.
According to section R806.3 of the 2006 International Residential Code (IRCInternational Residential Code. Many experts advise that 2-inch-deep vent cavities are even better than 1-inch-deep cavities; if that's the route you want to go, size your spacers accordingly. As with all types of vent baffles, it’s a good idea to pay attention to airtight construction methods, especially if you will be installing air-permeable insulation in the rafter bays. If you prefer, you can locate your ventilation channels on top of the roof sheathing rather than under the roof sheathing. In some cases, these ventilation channels are installed above a layer or two of rigid foam. If you are choosing to build a vented roof assembly, don't forget to include soffit vents and ridge vents.
As I noted earlier, researcher Bill Rose has exposed the unscientific nature of code requirements and formulas for calculating roof ventilation openings.
Most building codes require 1 square foot of net free ventilation area for every 300 square feet of attic floor area, assuming that half of the ventilation openings are located in the soffit, and half along the ridge. Manufacturers of soffit vents and ridge vents usually specify the net free vent area of their products on product packaging or in specifications available online. Most rafters aren’t deep enough to accommodate the insulation needed to meet minimum R-values required by code, especially if the rafter bays include a ventilation channel. Builders solve this problem by furring down or scabbing on additional framing below the rafters to deepen the rafter bays. Another way to add R-value to your roof assembly is to include one or two layers of rigid foam in the roof assembly — either above the roof sheathing or below the rafters. It is quite possible to design an unvented insulated roof assembly that performs well, as long as you get the details right.
First of all, you can’t use air-permeable insulation (for example, fiberglass batts, mineral wool batts, dense-packed cellulose, or blown-in fiberglass) to insulate an unvented roof assembly unless the roof assembly also includes a layer of air-impermeable insulation (either spray polyurethane foam or rigid foam panels) directly above or directly below the roof sheathing. E 2178 or E 283.” Although spray foam insulation and rigid foam insulation can meet this standard, fiberglass batts and dense-packed cellulose cannot. If you want to use just one type of insulation in unvented rafter bays, you are limited to spray polyurethane foam. The code restrictions on the use of air-permeable insulation between rafters were developed to prevent the roof sheathing from rotting.
It's important to note, however, that recent research suggests that closed-cell spray foam is much less risky than open-cell spray foam in this location.
Install closed-cell spray foam against the underside of the roof sheathing, and no other type of insulation. Install rigid foam insulation above the roof sheathing and air-permeable insulation between the rafters. Install a layer of closed-cell spray foam against the underside of the roof sheathing, and fill the rest of the rafter cavity with an air-permeable insulation. If you want to install a combination of rigid foam on top of your roof sheathing and air-permeable insulation between your rafters, you need to be sure that your rigid foam is thick enough to keep your roof sheathing above the dew point. If you want to combine air-permeable and air-impermeable insulation, there are two possible ways to proceed. Table R806.5 specifies the minimum R-value for the foam installed on top of the sheathing (not the R-value for the whole roof assembly) . After you have installed at least the code-mandated thickness of rigid foam above your roof sheathing, you should install the balance of your required insulation (in most cases, by installing an air-permeable insulation material like fiberglass, cellulose, or mineral wool) below the roof sheathing. However, in some areas of the country, especially in the Northeast, insulation contractors have been dense-packing unvented rafter bays with cellulose for years. If you’re building a new house, however, here’s my advice: if you want to insulate with cellulose, make it a ventilated roof by including ventilation channels under your roof sheathing. While vented roof assemblies are designed to dry to the exterior, unvented roof assemblies are designed to dry to the interior. If a building inspector insists that you install some type of interior "vapor barrier," you can always install a smart vapor retarder like MemBrain to satisfy your inspector. Yes, of course — especially if you are using fluffy insulation like fiberglass batts, blown-in fiberglass, or dense-packed cellulose. If you are building a cathedral ceiling, the biggest air-barrier blunder is to install tongue-and-groove boards as your finish ceiling without first installing taped gypsum drywall. Make sure to install insulation that provides at least the minimum code requirement for ceiling R-value.
I think the same strategy(vented over-roof) could be used to improve the Marc Rosenbaum type roof.
Do you know the original source for this photo and if it is possible to view other photos of this fascinating failure.
This project was in Vermont in a ten-year old home and as the caption indicates, the main culprit was leaky can lights in the cathedral ceiling.
I am including a photo of the solution: spray foam held down from the top edge of the rafters so that air can be drawn up from soffit vents to gable vents in the truncated attic cavity. Thanks for your suggested addition to the list of materials for making site-built vent baffles.
On an unrelated topic: The Cold Climate Housing Research Center has produced a video (below) showing one method of building an insulated cathedral ceiling. It seems if one were to use dense pack cellulose in a vented cathedral ceiling the vent channel material should be rigid enough to withstand the pressure. 4) Have there ever been moisture problems in any roofs caused by effects other than, first, roof leaks, and second, air flow of one kind or another? As Bill Rose notes, air tightness of the assembly, both inside and out, is of critical importance - we need to stop the air flow.
My sense is that if we are worried about air leakage compromising the insulation's effectiveness, vent channels are problematic. Regarding installation: While it's been successfully installed in Europe for many years, we've just gotten the material, and so we look forward to getting it on a job site soon and actually installing it - and of course, reporting back how it went.
I am with Martin on this one, your detail is labor intensive for little if any gain in my opinion. Admittedly these are new products for Americans but they've been used successfully in Europe for years - so not really new.
Regarding dense pack cellulose: not sure why dense pack would be negated - I think it perfectly suited. I like the detail provided but I wouldn't call that a cathedral ceiling condition as it includes ceiling joists spanning at the bottom of the roof rafters. Yes a cathedral ceiling detail would be very similar but the challenge of many cathedral ceilings is the added structural elements, electrical boxes, and the desire for wood board ceilings all which start compromising the drywall layer which in your detail is used at the air barrier.
I have to wonder if the failure in the photo would have occured if the hip and ridge was vented and everything else the same?
I was skeptical of Bill Hulstrunk's claim that AccuVent baffles could withstand being dense-packed in an enclosed cavity. To be clear, we tested the AccuVent cathedral ceiling extension, not the standard AccuVent shown in Joe Lstiburek's Fine Homebuilding article on roof ventilation.
I suspect that Bill Rose is right: all of these failures involve moisture that is carried by moving air. I think that people who write building codes are concerned that, if the code allows unvented rafter bays to be insulated with cellulose, failures will occur due to sloppy cellulose installation. But if the installer is conscientious, and the rafter bays really are dense-packed, my guess is that everything will be fine. Any home being built better than the absolute minimums should at the very least not use OSB for roof sheathing.
The main flaw in this roof looks to be the ice and water membrane at the highest point in the rafter bays. I thank you for this impeccably timed blog, as I am currently framing my semi-basic cathedral ceiling hip roof (with short ridge). Part C: Install treated 2x4's from eave to ridge, long bolting into each respective rafter. My understanding as I read this blog is that I do not have to worry about creating an air channel above the sheathed portion because of the rigid foam.
If your climate is not too severe it's probably okay to have just the R-10 foam over the structural steel, although there's some risk that the steel could sweat in cold weather. I am building a forensic laboratory constructed in Massachusetts, and am having a difficult time reconciling applicable building code with my read of the literature pertaining to insulation and roof deck condensation.
We decided to forego ridge and soffit vents during framing and roofing, trusting advice that an unvented roof insulated with spray foam was the better option. My read of the literature suggests a low to moderate risk of roof deck condensation for my building, which could be reduced and managed using airtight drywall installation and a low perm primer or paint. However, the applicable code does not appear flexible, with respect to buildings like mine. I would greatly appreciate recommendations from experts: bite the bullet and risk of spray foam insulation, or send the builders back up on the roof in December to cut ridge and soffit vents? I am designing a house and we are using cellulose in 2x12 roof rafters, and I came across a product that looked great.
Many spray foam roofing contractors in our market are touting their ability improve efficiency on old hot tar and graveled flat roofs by adding 3 to 4 inches of closed cell spray foam. As the head of our local HBA, I have strenuously pointed out that foam over a vented flat roof assembly does not provide the insulation values promised.
I want to promote cost-effective efficiency in my market, but not at the expense of roof failure. So the question is: seal the stucco vents and add the spray foam roof and don't worry about condensation? However, I presume those min levels are based on the assumption that total roof insulation levels are around code requirements given the climate zone, e.g R-38 for CZ 5 (roughly double the R-20 impermeable ins. Changing the Intelo membrane to glued & taped OSB or Plywood with a service cavity below made of framing lumber does make the assembly much easier to build. Yesterday we blew the insulation and installed the SIGA Majcoat on the CAPACES Leadership Institute.

Less than 45 minutes after the insulation was completed we had finished the Majcoat and were busy taping seams. We got such a huge response from the above photo on our facebook page – I just had to dig a bit deeper and find out if there is any plans. However, there’s still tons of great free dog house plans out there that are similar to the above.
Building a dog house is a project that most people will be able to accomplish, as long as they have fairly basic DIY skills.
Mark out the panels onto the siding carefully using a pencil and making lots of measurement’s.
Round the edges of the four 6″ pieces of timber you cut before, these are the legs of the dog house.
Then put the first piece of flooring down, hopefully there won’t be an overhang, but if there is this can be corrected by using a circular saw to trim off any extra wood.
Hi I would love to have the plans for that amazing dog house on the top of page thank you ! Hi there I was just wondering if there is anyway of getting the plans for the big wooden shelter with the German Shepard in it at the top of the page. The only stair cover kit available that meets the 2009, 2012, 2015 International Energy Conservation Code (IECC) and the 2009, 2012, 2015 International Residential Code (IRC) - used in all 50 states and most jurisdictions!
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In most cases, these ceilings leaked air, leaked heat, created monumental ice dams, and encouraged condensation and rot. In a well documented JLC article on roof venting (“Roof Ventilation Update”), Rose explained, “For the most part, the focus of codes, researchers, designers, and builders on roof ventilation is misplaced. This building component is known by a variety of confusing names, including a ventilation (or vent) baffle, a ventilation (or vent) chute, a ventilation (or vent) channel, or a Proper-Vent (a brand name). The one- and two-family dwelling model building code copyrighted by the International Code Council. Seal the edges of each panel with caulk, and tape the seams between panels with a high-quality tape. If you decide to do this, make sure that any roofing underlayment that you install above the roof sheathing is vapor-permeable — for example, #15 asphalt felt, VaproShield SlopeShield, or Solitex Mento — and that your local building department accepts this approach to roof venting. Although this approach is less fussy than installing vent baffles underneath the sheathing, it usually costs more, because most types of roofing require a second layer of plywood or OSB on top of the vent channels. It's also possible to purchase nailbase (a type of SIP(SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. If a roof has only soffit vents and no ridge vents, most codes require 1 square foot of net free ventilation area for every 150 square feet of attic floor area. Another technique is to add a layer of cross-hatched 2x4s, 16 inches on center, installed beneath the rafters. In addition to improving the R-value of the roof assembly, a layer of rigid foam has another benefit: it interrupts thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss.
In recent years, most building codes have begun to allow the construction of unvented insulated sloped roof assemblies. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Another possibility, of course, is to build your roof with structural insulated panels (SIPs). When fiberglass batts are installed in unvented rafter bays, the batts allow moist indoor air to reach the cold roof sheathing. Be sure that the thickness of the spray foam is adequate to meet minimum code requirements. If you choose this method, it's possible (though not necessary) to install vent channels between the top of the rigid foam and the top layer of roof sheathing by installing a series of parallel 2x4s — one above each rafter — extending from soffit to ridge. Guidelines to achieve that goal are included in the 2009 and 2012 International Residential Code (IRC).
Note that both types of insulation — the rigid insulation above the roof sheathing, and the fluffy insulation below the roof sheathing — need to be in direct contact with the roof sheathing.
Cellulose can only be used in an unvented roof assembly if there is an adequate layer of rigid foam above the roof sheathing or an adequate layer of closed-cell spray foam under the roof sheathing. Because the method has deep roots in New England, many building inspectors accept such installations. For more information on the theory behind roof assemblies and wall assemblies with exterior rigid foam, see Calculating the Minimum Thickness of Rigid Foam Sheathing.
A board ceiling is notoriously leaky, and this type of ceiling is often associated with roof sheathing rot. If you are using fluffy insulation, you need two air barriers: one below the insulation, and one above the insulation. The ventilation channel will provide cheap insurance against moisture build-up, and will lower the chance of ice damming. But the situation was exacerbated by an attached greenhouse, which communicated with the rest of the home, and a clothes dryer vented to the indoors during the winter.

This roof cavity is actively ventilated with a fan, not because the remodeler who did the fix was not confident about his new roof assembly, but because the owners were so gun shy of keeping their roof assembly dry.
The method shown in the video is particularly appropriate for builders in climates subject to ice dams. This would be a good insulation choice especially when using I joists, batt insulation is typically sized for dimension lumber and does not fill the space completely without modification. In How to Install Cellulose Insulation, Bill Hullstrunk said that he has had good success with AccuVent baffles, which are evidently rigid enough to withstand the pressure of dense-packed cellulose. But the "tipped-up commercial foam-based, no air-path sandwich" is a good approach, a keeper. The vent channels we describe can be done after the roof is on from the underside (dry side).
So at Bill's suggestion Jim Millhouse (also from National Fiber) and I ran a couple of 'tests'. Also, a small amount of material ended up on the wrong side of the baffle, which probably means folks would do well to follow Martin's advice on sealing them during installation. I'm not aware of any failures that have occurred in properly dense-packed unventilated rafter bays.
Some installers will fail to dense pack every cavity, and there will be rafter bays with air movement, and we'll be right back to having problems with sheathing rot. All the rot from warm wet air meets cold wood is right close to where a vented hip may have averted all and WITHOUT vent chutes. Would just regular felt paper have allowed enough moisture to dissipate through the roof sheathing avoiding rot?, I sort of doubt it. Using continuous Ice & Water Shield is sometimes risky, but it's OK if you are following the PERSIST approach and putting all of your insulation on the outside of the peel-and-stick. I really think venting a roof that is airsealed in the interior well and built without vent chutes is possibly the best way to build cathedral ceilings. It has what we are looking for: Good airsealing at the interior, fluffy stuff in the middle, and good drying channels for water vapor at the top.
There was more than 8,000 Cubic feet of insulation to install, so our insulators had 2 of their blower trucks and a good crew on site. Because there is an airspace above the insulation, I am confident that the small amount of moisture that got on the insulation will be able to dry to the exterior. These free dog house plans allow you to build quite a professional looking dog house that you can be proud of.
This guide will look at the simple dog house because it’s a good beginners house anyone should be able to build. Nail these to the long lengths you cut before making sure they are lined up with the corner. Then the wooden dog house can either be painted or stained to weatherproof it and make sure it lasts for as long as possible.
We have 12 week german shepherd and are looking for dog house her and I think Rylee would love the above dog house. Department of Energy's (DOE) Weatherization Assistance Program (WAP) and the National Renewable Energy Laboratory (NREL) for use in Energy Efficiency Programs. Even if you have an unusual construction, the Fireplace Plug Chimney Draftstopper can be successfully installed in less than 2 minutes. It reduces air-leakage through the whole house attic fan saving the homeowner heating and cooling loss and energy costs. Freedom pet Pass Pet Doors are the most energy efficient pet doors on the market and are easy to install.
Our air-sealed cover has been specifically designed to eliminate heat loss and stop cold air from coming into the house through the recessed light fixture. Making your home energy efficient will save you money and more comfortable on those cold winter nights. Kits are available in sizes from 15-600 board feet and provide a quick consistent flow of foam that dries in under a minute. These systems provide quick and easy foam application for repairs and renovations, new installations and production applications.
Our garage door insulation material consists of two layers of polyethylene bubble film sandwiched between two layers of metalized film. In many cases, roofers tried to solve these problems by improving ventilation openings in the soffits and at the ridge; these “improvements” often made every symptom worse. Instead, the focus should be on building an airtight ceiling, which is far more important than roof ventilation in all climates and all seasons.
That’s relatively easy on a gable roof without any dormers or skylights, but if the geometry of your roof is complicated — with features like hips, valleys, and dormers — it’s impossible to assure air flow through all of your rafter bays. At one time or another, it was possible to buy baffles made of polystyrene, cardboard, vinylCommon term for polyvinyl chloride (PVC). If you install ventilation channels on top of a vapor-impermeable synthetic roofing underlayment, the flowing air won't be able to help dry out the roof sheathing. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel.
That leads to condensation or moisture accumulation in the sheathing, followed eventually by sheathing rot. Remember that open-cell spray foam is risky in all climate zones, and if open-cell spray foam is installed in this location in a cold climate, the underside of the cured foam must be covered with gypsum drywall that has been painted with vapor-retarder paint. It can be ripped on a table saw and installs quickly, fiberboard does have a high perm rating and may allow small amounts of moisture to pass through into the vent space.
Or we strictly forbid complicated roof geometry, and blame future problems on designers of non-simple roofs.
A ridge is actually a corner, with all the effects of corner geometry (change in film resistance, radiant reflections, shape factors, etc). And if the answer is that air flow from below is always a partial culprit, then are we so sure of our roof-venting skills to make sure that our vent strategies provide pure dilution and play no role in inducing flow? I stop taking bets on cathedral ceilings that use venting in other than simple, straight-run, air-tight-underneath conditions. How easy is it to balance on the rafters as you install the membrane, presumably with staples, and then install the 2x2 spacers, presumably with nails or screws, all without putting a foot between the rafters? For those of us building in a cold climate this is a huge advantage, we spend as little time as is needed on the roof.
If the rafter bays really are properly dense-packed -- a big if -- the chance of air movement is very low.
Plywood clips do give a bit of spacing between 4 x 8 sheets and depending on the location may have helped with regular roofing felt. It provides up to 25.6 R-value in foam insulation (in thicknesses up to 6" which include a 1" airspace and plywood) while providing a cooling vent under the shingles, and easy installation for the roofing with the nailbase. So if one were to create an R-50 assembly, they better be providing R-26 impermeable insulation above the roof deck. By changing from a low permeability sheeting to a high permeability membrane (at top) with venting above, there is no more concern for roof rot while at the same time wind washing is prevented in the bays by the air & water tight membrane with taped edges and seams.
Here it is again (with the builders comments) I think it's a pretty straight forward build once you get past the idea of adding service cavities to your build. They were blowing cellulose as fast as they could and the the rain was heading our direction. When cutting the opening make sure it’s only just large enough for your dog to fit inside. The core of the door is 10" thick and made of Expanded Polystyrene foam that provides a greater R-Value per inch than fiberglass. Tested to withstand the equivalent of a 25 mph wind yet let pets enter and exit with no effort. Our air-sealed cover has been specifically designed to eliminate energy loss and stop allergens and pollutants from entering the furnace at the filter. Simply install two sensors to your power cables and a wireless transmitter will send usage data directly to the display in real time.
Our 600 board foot size kits include a free 30 foot hose and professional spray gun with your order of 1 or more kits. Our water heater insulation jacket features a highly reflective metalized aluminum film that blocks 94 percent of radiant heat. We do require a fee equal to the shipping cost to cover the shipping of the new Battic Door to you. When the moisture encountered cold roof sheathing, it condensed, leading to moisture accumulation and rot. Sometimes they included flimsy Proper-Vents between the fiberglass and the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate)., and compressed cellulose fibers. The roof framing cavities were filled with cellulose; the cellulose was air permeable enough to allow the can light penetration and wiring run lead the leaking moisture laden air up the rafters to the hip. Short answer is that buoyancy plays a big role in air movement, but stratification of still air does not. A lot of new products out there looking for a home with some tough construction details to make them work. While looking simple it still looks beautiful and is a practical place for your dog to take shelter from the elements.
Easy to use - simply open canisters, expose for 2-5 days, then send the test canisters to a laboratory for analysis with a pre-paid priority mailer (included in kit). Our garage door insulation kits can dramatically improve thermal performance and energy efficiency, keeping energy costs lower and interior spaces more comfortable. Our water heater insulation jacket provides superior thermal performance and energy efficiency and can significantly reduce energy costs. These days, the best available vent baffle is probably the SmartBaffle, which is made from polypropylene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. A cathedral ceiling can be energy efficient if built properly with high levels of insulaton. I am a plywood devotee and never use OSB anywhere but I think under the same conditions plywood would have failed also.
And do you think it is a better solution than not providing any venting, but using layers of poly iso over the 2x12 rafters filled with cellulose - a hot roof?
It’s also possible to make changes to the design and paint different colors to create a unique dog house.
You also get full insulation over the outside wall top plate which eliminates ice dam potential providing the building is airtight.
EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.
Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs.

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