Vented Attic Insulation? Here’s a trick We Stole From European Builders 

Based on the thermal differential between upper and lower lip. Assuming no anomalous thermal bridging by way of soup or milk stuck in the stash. We are seeing estimates around an R 1.4 - R 1.6. Which is pretty good considering it is a fully vented stash. I believe they were first popularized in Europe, but many people are saying they are making a big resurgence in the US as well.

Lol best description of a vented mustash ever 😂

😂😂😂

Probably the hardest I've ever laughed at a comment 😂

LMAOOO

10" Raised heel with R-65 CCSF......I think that is good enough

​@@stevenbaczekarchitect9431OK, I must have missed that in the video. So if you are filling from the top plate to the underside of the baffle with CCSF, how far in are you coming before transitioning to blown in? Seems you are still going to have a dramatic step change in R-value at some point. Like 65 down to 38 before climbing back up to the center at full thickness of blown-in?

You're blowing up my gable

There would be no issue with this detail in your climate zone

Why would this not be best practice in your climate zone? This type of assembly could be used in your zone and colder. I would not expect any mold issues specifically due to the use of the smart vapor barrier.

Comedians among us - love it!!

You cannot create a tight home without also adding in energy capturing ventilation systems. These have to be active. Building a tight house is like putting on a wind breaker over a sweat shirt. On a windy day a sweat shirt won't keep you warm. Add the wind breaker and you are comfy again. Start to move a bit and now you need to shed internal moisture. By controlling the ventilation, filtering it as it enters and then capturing heat and controlling moisture, you keep a house comfortable. Extra air "make-up" has to be added for high speed air extraction like big kitchen vents. That's been shown in other builds. The energy consumed with the active energy recovery systems is more than offset by energy losses you have in older style homes. This is at the core of good passive house design. Get this wrong and you have no end of trouble later. In high humidity climates, you may need to add central dehumidification, especially if your building is so efficient that the AC doesn't have to run much. Dehumidifying uses energy, but it's less than full AC cooling.

Sounds about right. I live in Washington State - King County Area​. I've been working on my house bit by bit, including 2x R15 layers of rockwool added as a base layer, with about R45 average depth of existing blown fiberglass on top. I extended the vent baffles by about double to get them well above the loose insulation rather than right at or a bit below the insulation level like before. I also went through and air sealed all penetrations from plumbing, electrical, lights, and wall top plates, no matter how difficult it was to reach. Tight areas of the attic are straight R60 rockwool like one side of the vaulted ceiling above the master bedroom where the down slope of the ceiling also has the downslope of the roof and comes to a tight point at the end. Moisture shouldn't be a problem in the attic now, but in the house during the fall it can get humid inside and before the attic project I had needed a dehumidifier to run. However that humidity primarily comes from outside when it's 60F average and 80-99% humidity all the time. So having a tighter home and controlling fresh air intake, and eventually something like an ERV would reduce the amount of humidity management required theoretically. In the winter its cold enough that humidity is not a problem, and summer usually isn't too bad but we'll see. Next project probably next summer will be replacing the rat feces/pee laced fiberglass in the crawlspace with new R30 rockwool and air sealing wall bottom plates and penetrations. I probably won't do encapsulation even though HVAC ducting is in there, but I'll have to do more research for my situation. @@andrelam9898

FYI there are homes and small apartments/condos built this tight in the Seattle area

@@andrelam9898 With just doing the typical sealing like zip wall and being thorough on details, it is often necessary to mechanically add fresh air because the house is already too air tight. I can' t imagine we need this product. Or that it wouldn't be more effective to just do spray foam and a conditioned attic.

I'm definitely curious how we'll look back at this period of time in building technology development in a few decades. I try to stay very open minded to new technologies and innovation - it's how we get better. But, my skeptic hackles spike when I see all this stuff. For now, I'm sticking with tried and true methods, and letting other builders experiment with the new tech. As time goes on, the best products will reveal themselves and I'll start incorporating them as well.

Yeah it’s amazing how far behind the states are in some departments

There is a 10” raised heel. There has to be a balance between heel height, roof pitch, height of the building and overhang relationship to the top of the windows on that floor. This was the best overall balance given all those factors.

Also understand, using a 10" heel with a flash of a couple inches of CCSF, you get R-65 at the plate

Just a truss screw sealed in the wood - not really contributing to Air leakage.....

Agreed

Appreciate the comment - sometimes your comment may be true, but here we need to hit .30 ach 50 (clients wants sub 1.0) and the code requires R-60. Ok take out 5" of blown in insulation (that would pay for itself in as many years) - how would you detail the ceiling / roof to hit 3.0 ach 50? You have to do something? So, what would you do? How do you design this detail?

@@stevenbaczekarchitect9431 I personally would just do spray foam. That seals the house and seems like a lot less labor and issues for lighting and penetrations. Also makes for a very clean and accessible attic space.

Good info!!

Another option is to get a pump hand sprayer and spray your eaves, soffits, and vents every 2-3 months in the spring & summer with something like Tempo SC Ultra. I do that along with spraying around the house foundation and do not have any issues with insects inside the attic or the house itself.

I’m about to do something very similar including doing t & g soffit under the eaves so I can seal up and re-screen the vented blocks.

I'm about to do this type of work in a bungalow with a south facing half of the roof which gets sun all day. A bungalow with a finished upstairs goes from 1 big attic to 3 small attics when you finish the upstairs. The two lower ones need to be vented, and they're not on most bungalows, causing the upstairs to really cook in the summer. When the lower ones are vented, the vents serve as cold air intakes for the air to travel up the inside of the roof rafters and exit the gable vents at the top that was already there before. It was a bummer finding out in this video that loose fill gets blows around when you vent an attic because I have loose fill and the south facing lower attic needs to be vented so badly. I'll probably do what you do with two layers of rockwool underneath and then loose fill back on top, and do it in sections like you did. The gable vents that I bought from home depot already have a mesh on the back which looks like the holes are small enough.

@@readtherealanthonyfaucibyr6444 consider solar powered intake and exhaust fans to compliment the gable vents. Also, for the vented eave blocks, there are spacers that maintain the air gap creating a duct/chase for the convection path. The loose fill doesn’t blow around much at all once it is installed by “blowing it in”, the air exchange doesn’t move any appreciable amount of the loose fill around

Can't go wrong

Dam mices

It would be more expensive here

I wouldn't listen to that friend very much - what's Crazy Complicated? Putting up a membrane is complicated?

It can't and I never said it could, you just need to be very diligent about any holes........as if!

It's smarter......the truth

@@stevenbaczekarchitect9431 OK, but I was hoping for some details?

The 2X4's are 16"OC

I would argue exactly the opposite, but it is a free country, fell free to go roll the dice

He has, but we did this in the late 90's at Building Science Corp

I would never put poly in a code built home today - metrics are different, but you go roll the dice.

It's an adhered membrane

It would look the same

Agreed

Smothers brothers

Oh yes it most certainly does, actually that is the reference from the manufacturer uses, take up the semantics with them

Who's the boss lol?

It for sure requires heavy management from the gc. Not something I would install on a project I didn’t have a fair amount of supervision on.

Always lurking in the building corner's coming up with new ideas to old problems - I do appreciate the concern...

Steve has a youtube channel that he uploads to several times a week

Is matt getting paid for this, seems like such a left turn?

Where waS there poly? Usually urethane. And it's a budget build ao they can't do every product thats best of breed

You should be out of the house before an EPS board sandwiched inside a bunch of gypsum board and whatever exterior sheathing becomes a threat to human life. Sure, I'd like to live inside a concrete castle, but everyone can't afford that luxury. But everyone can afford smoke alarms.

Cellulose, Nu - Wool to be specific.......and of course this will last

Great question. This has to be at least 1/2 to 1/3rd the cost but it would be good to get actuals for a future video.

Thanks for the comment

I also agree on the Building Practices.....

I have seen 14’ walls with blown in cellulose settle 2’ around the whole upper ceiling.

There is a 10” raised heel.

@@brettpelletier1219 my idea of a raised heel is to allow a uniform insulation thickness all the way out to the edge of the wall. Otherwise any truss that keeps the truss top chord from touching the wall plate would be considered a “raised” heel. A true raised heel also makes for larger overhangs, a good thing from a durability perspective. I guess something is better than nothing. Also, a 10” raised heel needs attic vents installed, so that takes away from the thickness of the insulation as well. I see they also needed to spray foam this area to seal it. Using a true raised heel truss you can fasten strips of OSB to the trusses and seal with acoustic caulk or canned foam. Were small overhangs a styling decision or wind load requirement?

@@superspeeder I agree with you that the larger the heel the better and in an ideal world it would match the depth of the insulation. We have 2’ overhangs which I would consider fairly large. We had to balance the height of the building, pitch of the roof, overhang relation to the top of the windows on that floor, etc. Overall, with all these factors we arrived at what you see. There are always things that could be done better from a building science perspective, we’re just trying to do our best to strike a good balance.

@@brettpelletier1219 thanks for clarifying! Agreed, there are often compromises made that aren’t always obvious. I’m in the process of building my own home and these are all things I considered. I have 3’ and larger overhangs with an 8:12 pitch, so lots of room for raised heels and simplified attic venting details. In my area, maximum building height per zoning regulations was not an issue so I had lots of design freedom. Cheers, and good luck with the build! Looking great so far!

@@superspeeder that sounds like a recipe for success! Thank you very much and best of luck with your build as well.

In areas of Canada that can get very cold I would worry where that moisture would start to freeze and depending on what insulation is in the attic when would problems show up. I'll stick with my poly. Like the strapping on the ceiling chase idea though, to help protect the vapor barrier.

​@@kerrryschultz2904I like the blue material over the top plate too..

They mention at around 7:30 that for colder climate zones you would use a vapour retarder (like poly).

I've been asking the same question. They say the majrex allows moisture to come out of the wall but if the interior wall is covering it how does it pass through that?

That' good air tightness, but the permeability of OSB is only around 2-3 perms......

It isn't and a few companies have smart vapor retarders, just need to google it......

Aren’t all his videos these days basically infomercials?

The siga majrex is taped to the bottom chord of the truss with a tenacious siga tape, then the 2x4 strapping is nailed over that to the bottom chord of the trusses. The 2x4 strapping provide more than enough support for the blown in insulation that is to come. We’ve successfully used this approach before. The one directional nature of the majrex allows any potential vapor from the warm side to pass through into the vented attic. The blown in cellulose is vapor open as well.

@@brettpelletier1219two things; First the 2x4 of course strong enough to hold, more thinking of the span between 2x4 strapping. The insulation will weigh on the VB causing it to stretch or pull off staples or tape holding it in place etc. Also two things with the vapour drying I think possibly problematic. First you don’t want and moisture passing into the attic insulation, that’s the point of VB. Also the main of my original point is that when there is a cavity there between drywall and VB, the strapping will take some moisture which regardless if the drywall breathes or this new VB breathes it’s the point that the wood will not dry as quick. So standard 6 mil poly when done flush on drywall the strapping, moisture form warm side of poly directly on the drywalls back. Moisture has no other choice but to go into drywall and dry to inside. But everytime (not exaggerating every single time) I’ve seen the VB on the truss, and then strapping the cavity created has moisture forming. Yes it will dry through the drywall, but it’s now wetting the strapping somewhat. And that strapping is slower at releasing moisture. My understanding of the smart VB is that it can function both way. As in when it’s warm inside and cold outside it should act as a normal VB. But in the summer and it’s warm outside, and cool inside with typical poly VB now the moisture forming on the warm side which is the insulation contact side. That’s bad because with dual climate -30C to +30C poly VB only works in one season properly. That’s what the smart VB works with isn’t it? But regardless if it lets moisture breathe to the insulation that’s a problem isn’t it? literally the reason we use poly VB in the first place is to not let the moisture form in the insulation. Cellulose or fibreglass regardless they’ll all be open breathing, the issue is when that reaches the top of the insulation depth and hits the cold attic air it rapidly condenses causing mould. Not trying to call anyone out, jjst trying to see if there’s a missing link here.

@@justinstevenson2061 my mistake, I see what you’re getting at. The 2x4 strapping is spaced 16” oc. I agree with your line of thinking here in regards to the science and your experience with how moisture moves, I just don’t think the real world application will be an issue here. We have dedicated dehumidification and this assembly isn’t trailblazing. This approach has been used successfully in many high performance homes and we’ve had success with it ourselves.

@@brettpelletier1219 oh yes absolutely. I’m just the retro fit insulator. Main trade roofing, naturally moved to siding, and then natural to insulation. Have to do siding to swap wall/step flashings effectively. And have to understand insulation and venting to do roofing/siding so they all fell together. I’m always baffled these idiot mass builders don’t for example put poly over the interior partition walls to connect each rolls VB continuous. Literally have said this for many years now. Also as to why when they lay tyvek strips on top exterior plates is it only for the exterior tyvek to join, and never hung over the inside to join to poly. Yes both different uses, but can at least air seal and still not trap as tyvek to VB not creating any double VB scenario. And literally 9 days ago o jjst started leaning about smart VB, so when I saw this video I was crapping myself. Like everything I’ve seen as failures and wanted to address (just haven’t made the jump to build yet, want to but nervous lmao even if I know more than most custom builders I’ve seen hacking it up on 2 mil builds) but all of those failure are addresed in this vid. So two fold I pat myself on the back to say “it’s not what we’re taught but what we can come up with” but also to show this system in full use by these two in the vid, and it being in practice more in Europe so tried and results noted. But also then even with perfect poly VB (before learning of smart VB) over partition walls you still have penetrations, and that’s another mass failure. So this method of 2x4 strapping to me is incredible. But then started thinking of strapping dead air space downfall. Wondering if siga on bottom chord and then drywall or plywood etc (whatever has higher vapour permeance) then strapping and interior finish drywall. Only strictly for weight of insulation. But to run electrical and some horizontal plumbing etc is brilliant. But then still the same air space problem I’m bothering myself with. Between the two layers of drywall the strapping is still where vapour can be. But at least my way I’m thinking the vapours not forming on the strapping at the siga, more it’s forming on the ply/drywall at the siga, and then drying to the cavity and then drying to the home. I overthink things ridiculously. My metal roofs are double strapped and ridge vented. Not many do it but some do. But they also cut the ridge wood and use that ridge vent to vent attic and under metal panels. I don’t cut the ridge wood, and the ridge vent is only for under panel venting. I then use a stack vent like a Maximum to vent the attic. Yes the detail to vent the attic through stack vent through double strapping and make stack vent watertight while using hidden fastener metal panels is a pain, I custom make drip edge with drilled holes on a horizontal 1/2 bump out from fascia as an intake for under panel venting. But all in all that house won’t suck heat, metal will expand/contract far less backing screws (even with plastic washers) but I just am as mentioned self admittedly way over the top. But that how innovation happens right? Im just wondering how 20 years later the strapping and moisture diffusion will go. Not saying you or these guys are causing failure in any way, I’m just killing my self thinking as I always do. This system is still far far better than what’s out there for sure, just wondering what the next step will be. R&D takes us so far, trial and error is where we inevitably learn. I love the soprema cardboard vents, as opposed to the stryo. The cardboard is better manipulated to fit the truss heel, and if there is any issue (Reno’s down the road and some mook makes holes and doesn’t seal them) and hot air rises it then condenses on the styro rafters where cardboard will breathe outside. I’ve had people ask, well cardboard isn’t as water resistant as styro, I tell them then you should make sure your roofs kept in good shape 😅. Ideally if I do your roof and attic you’ve got not damn worries anyways.

@@brettpelletier1219 I appreciate your responses, and no I’m not going to seek help for my overactive thoughts, I enjoy stressing myself it seems.

It's a VENTED ROOF

Thanks!!

Appreciate this - people talking about how this is overkill......it's an Air Barrier and some additional insulation

The danger is poly is not vapor open, Mayrex is...

@@stevenbaczekarchitect9431 Thanks for the reply. In Canada zone 5, 3000 square feet, with HRV. It used some techniques that were not common at the time, was affordable, and could be heated in winter by inviting a few people over. 🙂We did not know about Majrex in 1992. Was it commonly available in Canada then?

@@gregh99 im a younger tin basher, I was born in 1990! No it was not common in fact its a newer technology. Im in zone 6 in canada and it also wasnt necessary in 92. Its only with the onset of much warmer, more humid summers and an increased use of central AC that its needed. Instead of only worrying about water vapour condensing in the winter we essentially have a summer situation that is similar to a southern set up like texas. Hot humid air travels inwards through the wall from outside and hits the cold air on the interior of the house and condenses on the back side of that poly. Mayrex is the solution to this. Poly should be banned in Canada and smart vapour retarders should be the new code. But back in 92? Id say you where being forward thinking. Its so easy to make these decisions with the level of building science education now adays thanks to youtube but 92 was a different beast, I dont even understand who you guys managed a business without widespread cell phone usage haha

Yup, he bought me lunch

Well thank you - even though I didn't ask, should I need architectural criticism, i will keep you in mind

The cost isn't worth the result

@@stevenbaczekarchitect9431 They used spray foam to achieve the same thing.

“Can lights” in the era of LED lighting should really amount to the low profile units that can easily fit below that vapor barrier. If your customer tells you they want old-school cans, show them how much better the new options are.

@@shawnbrennan7526 The "wafer" or "pancake" lights that you mention are more suitable for tract homes or the DIY'er. I'd compare these type of fixtures to using traditional OSB and house wrap for the wrb. If your customer desires can lights, then do them a favor and get regressed cans at a minimum. This will greatly reduce glare. Good can lights, which typically require a housing, also provide the option for different trim/flange color options. Good can lights will also provide more consistent CCT between fixtures, dim more consistently, and provide a greater dimming range. The best option would be tape and channel, which would work great for this detail, but budget is a factor just like every other decision. Most of these videos are geared towards a higher end client and I can't think of an application where I'd provide a $25 wafer can light for a house I was building for myself or specifying for others. Owners interact with their lighting every day. Remember that they can actually see their lighting whereas they cannot see their air barrier. Both can greatly contribute to occupant comfort.

I can't say I see as California as a leader for what I should do......

Some of the energy recovery air handling systems use very little power in contrast to a leaky home that requires much more energy to heat or cool because of the excess air exchanges per hour.

You might want to look into how an Energy Recovery Ventilator (ERV) actually works instead of comparing it to an open door.

@@LooseNut - I think that is where the code is going but the cost of regulations has become so high there is beginning to push back . Panasonic makes a reasonably priced one but I question the longevity.

@@LooseNut It was @markmarcinik that was talking about tightening the envelope causing indoor air pollution requiring a fan running 24/7. He said might as well keep the front door open. I know exactly how an ERV or HRV work because I have researched them since the 1980's. Ill informed people that think a drafty house with all the energy loss associated with poorly built houses probably have never lived in a building approaching super insulated standards with adequate ventilation through out the house to remove excess humidity and stale air or damp and odour that a proper house should provide.

This is an interesting idea. Dunno if I like it considering electrical in the ceiling but... non flammable/ flame resistant foam....

I've seen people do it only at the drywall joints where air is likely to make it's way through. Also a lot cheaper than spraying the whole thing.

Open or closed cell?

I don't know about production housing being the standard???

OK good to know somebody is out there doing things I wouldn't. Enjoy

Yeah, they could have continued the majrex down to the walls and air sealed from the inside. That does require a service cavity or extra detailing to keep the airtight seal going. This seems like a somewhat budget conscious build given the vented attic which Matt typically avoids so maybe they didnt want to pay for the additional labor for that detailing.

I am fully aware of how you all do it - I appreciate it, but I do not agree with it for a wood framed building. For your Masonry buildings yes - wood frame here, NO