Roof Insulation vented
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- čas přidán 27. 09. 2015
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Funny how this was years ahead of subsequent vids on other channels. Says a lot.
I was teaching a class to MN contractors and apologized for how old the video was, but then realized, "heck, why is this new to people? We've been publishing videos on it for almost a decade, and I was covering it for other construction journals for a decade before that."
Looks like a great way to Upgrade the Roof insulation wish I had seen this Video before installing a new roof 2 years ago Now I have to do it the hard way from the attic. Thanks for making this video.
In the continental USA 3rd quadrant (think Cartesian plane; i.e., the southwest) it makes more sense to use a vented sub-rafter radiant barrier. Eave vents for air intake; ridge vents for exhaust, by convection current. This is the competitor to high insulation values, and is a finesse solution to passive energy conservation. To use high R values of insulation is to "force it." This makes sense in Minnesota and Massachusetts. The radiant barrier is superior in California, New Mexico, etc.
Adding insulation is definitely good. Adding weight may not be possible or safe for all roofs.
I bookmarked this to add to relevant vids for the 2.5 story extension with thick walls. Thank you ever so much☺ 👍💯 🙏💝🇨🇦
Glad it was helpful!
@@ProTradeCraft A lot of what you present is so practical and makes sense in home building. What is interesting is seeing the "effectiveness" of your teachings and Joe Lstiburek's when I interview builders here on Prince Edward Island. The solid knowledge base, building science and air tight details I mention in the interview and for what I listen to when a potential builder talks has these builders taken off guard! The consequence is that they realize they cannot pull the wool over my eyes thinking that they are the ones for the air tight thick wall and roof assembly build. All this "PhD study" of your vids, Lsitburek's, Risinger's, Baczek's is limiting the choices out here to find the right builder. But, can you imagine if I didn't have my "PhD in building science" from the school of ProTraceCraft, Lstiburek, Risinger and Baczek! The build would possibly be most disappointing. Thank you again for all the education and effective visual affects and detail. As Steve Baczek says, "Long live our houses." ☺👍 🇨🇦. 🛠🪜🪚
this is my exact garage, thanks. Now I know what to do.
Thank you!
Reminds me of my idea for what I called a double decker roof assembly. The idea was for zip sheathing over roof framing taped and wrapped then the 2x4’s on their flats for the air gap then another layer of radiant barrier roof decking. Goal was to minimize radiant heat flow to almost zero.
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@Rohan Wallace instablaster ;)
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Now That's A Quality Roof.. Good Video, And Damn Good Work.. Jus Sayin.. Yep...
Thank you.
Great design
Well done job, I live in Brazil, and I would like to make a roof like this in my house, and I would like to know, what is the minimum distance that should leave between the ceiling and the OSB, thanks in advance, Ps: My house have no attic
I'd like to see the monopoly house design from Matt Reisenger's Build Show. The ladder blocking goes outside the exterior wall foam.
?
@@ProTradeCraft Your box beam is a thermal bridge
As mentioned in the video, the foam on the roof extends beyond the outer walls *to later be incorporated into exterior wall insulation*
So the thermal bridge is there, yes, but thermal bridging has been eliminated on the entire roof deck.
And the ladder beam would later be removed when the owner adds exterior insulation under their siding.
Is this suitable for colder climates? Will this method keep heat in as there seems to be a gap at the soffit where warmth could escape. Maybe the foam overhangs enough on the outside to allow internal heat to build up and stay. How breathable is this roof? Thanks.
Can you please comment on the design of the top ridge of the house? Just a regular ridge vent? Any details on a vapor open or closed membrane? Interior insulation recommended as well, what type?
Excellent. I learned more from this little 2 minute video, than hours of culling through others. I’m just going to substitute rockwool over foam. You were brief, to the point. I enjoyed your wall vented video as well. Only thing that I would have liked for you to cover, is how to handle the peak at roof. Since heat rises, seems like at peak, it would be released there. Did it just stay completely closed up? TY for this wonderful little video.
Glad it was helpful!
For this vented roof, you'd install a ridge vent at the peak -- of course, it would be above the insulation, as the inlet vents are also. air comes in at the eaves and goes out through the ridge.
Nice jazz
Does the roofing membrane create a water/vapor barrier? Or is that something that may be product specific? Thank you.
So, you still have the coldest air at the sill, not at the ridge. Is this right?
Adds a lot of weight to the structure. Be sure the roof can take it.
What will it like after you put your gutters on ?
Why not foil faced insolation?
What climate zone is this used in?
Yes... now you dont have any more money to heat it.......lol
YES! Now how do you cover the rake edge? Do you treat it like a corner of a wall (take peel and stick and adhere top layer of XPS to rafter)? If fascia is applied directly to peel and stick and rafter need a thermal break?
Did you ever get an answer ?
@@cheeseburger9232 still pending (doesn't look like its coming). Any thoughts?
@@treystills the only thing I can think of , is having a sheet metal shop make a custom drip edge.
(Opps - first time I have commented on a video.) Now to my question - I need someone to do this kind of work on Cape Ann in Massachusetts. Are there roofers or construction companies in my area that have done a lot of this. The roofers I am speaking to seem pretty unfamiliar with the process. I have a 1935 open rafters home and am trying to put as much insulation on the outside as possible without making the house ugly. Thoughts? Recommendations?
Did you find anyone in your area to do the work? Was it successful?
Yeah, how’d it turn out? I’m also in ma and need energy retrofit and structural stuff done.
I wondering if this will work when you have no attic.
Will condesation form on the first old roof deck?
Can the rockwood insulation touch the old roof deck ?
You always need a little air exchange. Much less then before, but still some. A gable fan is the preference in a situation like what was described here.
You need the correct ratio of insulation on either side of the original roof deck. I *believe* it is minimum 40% outside, but don't quote me on it. If you get the ratio right, that deck will never get cold enough to condense moisture from the inside air. You can also spray foam the underside of the old deck (min 2" closed cell) but I don't know how that would work with the membrane on top.
There is a ratio as @jasexavier describes, and it is climate dependent. 51% to the exterior in these parts (DOE Climate Zone Zone 6a).
Do NOT listen to dekonfrost7. It makes no sense to tighten and insulate the slope of your roof, then to introduce air beneath that air and thermal control layer, with a powered fan no less!
dekonfrost7 probably thinks houses need to 'breath' and interpreted that to mean they should leak air. No! They need to manage moisture and to provide enough fresh air for occupants, but it's not a good idea to provide this fresh air via a leaky roof-it is likely to be too much or some unknown amount and could introduce moisture problems in your roof.
How does it do with solar? Will the screws hold all that weight trying to slide off the roof?
The 2x4s should be screwed into the framing below the foam, so yes, this should work well with solar. Especially considering how much energy WON't be needed to achieve your solar goals.
the 2x4s, sheathing and final roofing over the rigid insulation sheets don't seem like they'll work out too well. Especially on steeper pitches
? the detail was not invented; there are a lot of houses with it that work very well.
What part of it don't you think would work out so well?
Is the second roof deck absolutely necessary if installing a metal roof? I'm trying to add exterior foam without essentially doubling the weight/deadload on my roof rafters.
No, but you'd want the furring strips to be perpendicular.
@@ProTradeCraft or diagonal?
How does this preserve the "ridge" vent required to prevent ice damming? Also, we just had our house re-sided (with the insulation in the siding). Do we have to close off the rafter cavities for this solution to work?
How would this translate to a log cabin? I also need to replace some of the log rafters because of rot or critter holes.
Well, it has nothing to do with the framing, it's an add-on atop the roof, so it would translate well.
@@ProTradeCraft The roof will meet a log at the bottom, it is not straight edges or something you can cut out like what you have in the video. As I have to replace some of the roof support, I wasn't sure if I would need to start over anyway. Great video, thank you!
You didn't put a drip edge on the new roof, why?
They are only including the relevant details of the insulation retrofit. Things like drip edges and gutters are just normal parts of the roof finishing.
Add a radiant barrier (aluminum film)
on top of the foam board insulation and
under the new rafters(for venting and overhang)
:-0)
PS Overhang is almost entirely for looks, so save bucks with a new look LOL
2Truth4Liberty in areas with a decent amount of rain - overhangs are very important for keeping as much water as possible away from your walls
I would disagree that you need to keep "as much water as possible away from your walls"
as an important part of longevity of the wall.
Further, with wind (that usually accompanies rain) that area of protection for the walls on most houses is only a few feet of the top of the wall.
It is MUCH MORE IMPORTANT (cost effective as well) to protect the very top and bottom of the wall along with around each window.
Walls and windows will naturally dry quickly "on the OUTSIDE" with scarcely any harm over many many MANY rains, but moisture INSIDE(behind) will NOT naturally dry *quickly*.
Again -- "Overhang is almost entirely for looks, so save bucks with a new look" :-0)
Unless you are in a deluge, an overhang will keep water away from / out of the soffit vents and hopefully, prevent a large amount of the water from getting behind your siding ( czcams.com/video/kKBe9XVDMmw/video.html ); adding to that, having a rain screen system will allow the wall to dry out when it does get wet (but a good overhang should keep the top of the wall, at least, from getting wet). Additionally, a properly sized overhang can provide shelter from the sun for the walls- helping to keep the house cooler in the summer.
@Mr Sunshines The overhang does a very good job of protecting the top 12" of siding Einstein. Unless u live at the equator and it only rains straight down at your house . . You dont and neither does the man that started this thread.
On shorter overhangs (less than 12") I would partially agree with your assessment of an overhang being superfluous. But on a building with a greater overhang ( 24" or more) it goes beyond looks or curb appeal. The wider overhang, especially on 1 story buildings (like a ranch-style house) provide much protection from moisture and greatly extends the longevity of the siding material, doors, windows and the paint job. A wider overhang can also help shed water further from the foundation reducing hydrostatic pressure on the foundation wall. Ever seen a bowed in block basement wall caused by moisture and freeze-thaw cycles? I have. Also, wider overhangs can help shield the house (again 1 story) from the detrimental effects of direct UV from the sun.
what is your spacing on the screws and what about gable overhangs
Spacing is probably 16 inches, but you could ask an engineer. In New England, a lot of houses don't have gable overhangs, but if you want one, extend the plywood past the gable wall and build a box beam like you did at the eaves.
Anyone know the name of the mesh/bug screen block? I googled around and only found regular bug nets, not blocks like in the video.
Use a mortar mesh as found in masonry for use behind bricks.
That seems like a lot of extra weight. Are you sure those 2x6 old house rafters are ok with that? Not to mention the walls supporting the roof?
I would be more concerned with the rafters than the walls, but foam insulation literally weighs almost nothing. An extra layer of plywood and some 2x4s are probably not going to be too much, bit if you are concerned, ask an engineer to calculate it.
How are you going to handle the moisture migrating into the attic from the home since it's no longer ventilated?
This design would work only if your attic is part of the conditioned space. Otherwise it makes no sense to insulate the roof (greater total area) and you would put your insulation in the attic between/over the trusses instead.
An attic does not need to be vented, a roof does. This brings the attic into the conditioned space. You must not have insulation on the attic floor if you do this.
@@AnthonyBrusca if you don't have a dehumidifier in the house, yes you do. Originally the house is insulated in a way that allows the moisture from the living space to be ventilated through the ceiling up out of the attic.
Yeah not venting over living space in cold climate zones is asking for trouble. Also who uses screws on a roof? Good way to get roofers and firefighters hurt or worse.
@@JohnComeOnMan Roof venting is NOT to evacuate interior air. It's to ventilate the underside of the roof deck with outside air (hence the soffit intakes).
A roof over a roof? How is the extra weight of the second roof calculated into the existing structure? Any reinforcement needed to be added to the rafters of the first roof? 2 x 6 not enough space for insulation? Really? What about Fire Safety issues? If there is an Attic fire the Fire Dept will have serious issues getting through that roof.
Foam is 2 pounds per cubic foot. A 4 inch depth only adds 2/3 pounds per square foot while providing R40 insulation. The roof can support this easily. A slight breeze creates more force on a roof than this insulation.
The 2x6 has plenty of space for insulation, but they also provide a thermal bridge for cold and heat - the foam prevents that turning the attic into an internal space.
Chainsaws are standard equipment for firefighters trying to penetrate roofing. A Chainsaw would cut through that foam like a hot knife through butter. Not sure why you think it would be "a serious issue" getting through.
That brings up a good question. . . The roof on fire would create a real issue, 4" of foam turning to soup under the plywood. Could be a challenge. Good point.
Extra weight should not be significant, as rigid panels only weigh a few pounds each spread over 32 sq ft, and the second layer of sheathing (OSB usually) is only another 25 lbs or so spread over 32 sq ft. Roof trusses/rafters in the north are usually spec'd at at least 3x expected snow load. Snow load with wet snow can be 20 lbs per sq ft, way above the less than 1 lb per sq ft of the added roof material. A 2 x 6 rafter is not to code in the north. Typically you'd be using minimum of 2x 10, and more likely 2x 12. Pack in 8" of R5 per inch to get R40 and another 2" exterior to get a total of R50 and you'd meet code in the north. Even better to add another 2" on the exterior.
What is the mesh thing? Looks like a 2x6 at first. Does it restrict airflow?
the mesh thing is something like Coravent, or a masonry ventilation mesh. it allows airflow and discourages bugs.
Is the attic a conditioned space?
@Mr Sunshines You're an ass. . . So, u were born with perfect understanding of everything? I didn't think so, hence the "you're an ass" comment.
also shows no venting up into the attic
The roof is vented, the attic is living space.
Anybody doing this with mineral wool? I don't like what styrofoam does in a fire. Is there a mineral wool product that is rigid enough?
there is sheet type mineral wool but mineral wool will likely compress with the weight of what goes on top of it unlike ridged foam which is why they are using foam. personally i would use high density "Styrofoam" as it doesn't absorb or hold water.
Yes, people do it with mineral wool. RockWool has a board product that is used for this purpose.
How does the torsion box extend to the front overhang?
the same way: roof sheathing extends out, ladder blocking runs up the rake...
Should this roof also have insulation between the rafters?
It can and should, but you need to think about your air/water barriers, and where the condensation point will be. When you do something like this, you are implicitly including the attic into the "conditioned space," which can change your other computations.
If you do, you need to make sure that the ratio of interior to exterior insulation is correct, to avoid condensation on the old roof deck.
How thick is each sheet of foam insulation?
in this example, I believe they are each 2 inches thick
My research suggests this technique should perhaps be coupled with a “vapor diffusion port“ at the ridge. Thoughts?
well, it would be a standard ridge vent, as the ventilation is introduced at soffit vents.
Vapor diffusion ports would be used for an unvented roof with insulated rafter cavities.
Good job digging up the latest in. roofing science, though!
Install 2x4s over rigid isolation panels? No exhaust vent?
Exhaust at ridge
@@ProTradeCraft conventional ridge vent?
If you vented in AMONG us you sus
Could you estimate the cost to replace roof like this?
if you have to ask, you can't afford it ...
@@anon7039 That is a stupid answer, so you would just start ripping away your roof and think about the price when the job is half way finished?
It's not hard to price out the materials. Start by measuring your roof.
@ Thoracius Appotite
is correct, you would need to find the area of your roof first. do some math to find how many sheets, rolls and shingles you need. roofs are often calculated in "squares" which is 100sqft/square or a 10x10 area. 4x8 sheet goods are 32sqft per sheet. don't forget things like any ladders, lifts, fall protection, permits or other hidden costs like delivery. you are likely to need a tarp to cover the project as it's unlikely you will finish it in a day or two. add the cost of beer and pizzas if friends help.
Will the insolation extend the life of the shingles?
@Mr Sunshines Wow, you're an arrogant douche-bag arent ya? Bet ya family just loves seeing u pull in the driveway at Thanksgiving. Not.
generally, UV breaks things down.
can this be used in canada?
Yes. I am going to refrain from any exchange rate jokes.
@@ProTradeCraft what do you mean
mj
You must think we are all made of money. Thats a real extreme thing to do to a house. Im just not cool with this even IF I had the money to do it.
I do not think you are made of money, I think you are made of carbon, water and guts like the rest of us.
I do know, however, that energy gets more expensive every year. Insulation that is bought and paid for never gets more expensive.
if you don't like it, don't build it. If you want to leave your competitors in the dust as energy codes ramp up (they never get easier), then learn this stuff. Your choice.
Most old houses have vented attics, so why would rafter dimension matter? Just blow in insulation over ceiling joists. This is a dumb video.
Most old houses have vented attics? What's your source on that? Every Cape and many of the Bungalows in America do not have a vented attic. They have insufficient insulation between the rafters.
Not to mention all of those flat-roof houses in California.
Or the people who want to convert that unused attic space in theor ranches and four-squares into living space...
If you have a flat ceiling and vented attic, then blowing a lot of insulation into the attic is a great option - if you air-seal the ceiling.
@@ProTradeCraftwhat if you dont air seal?