Preventing Ridge Rot In Conditioned Attics (Featuring Dr Joe Lstiburek)
Вставка
- Опубліковано 6 вер 2024
- Check out Joe's articles mentioned in the video:
www.buildingsc...
www.buildingsc...
Building Science's Newsletter:
www.buildingsc...
Delta Foxx Underlayment:
www.dorken.com...
Ultra Aire Dehumidifier:
www.santa-fe-p...
And another great article on using Mineral Wool or Fiberglass in a Conditioned Attic.
insulationinst...
Follow Matt on Instagram! / risingerbuild
or Twitter / mattrisinger
Be sure to checkout our new Podcast!
buildshownetwo...
For more great video content check out Matts new site! buildshownetwo...
Sign-Up for the Newsletter buildshownetwo...
Build Show Network on Instagram / thebuildshow
Huge thanks to our Show sponsors Polywall, Huber, Dorken Delta, Prosoco, Rockwool & Viewrail for helping to make these videos possible! These are all trusted companies that Matt has worked with for years and trusts their products in the homes he builds. We would highly encourage you to check out their websites for more info.
www.Poly-Wall.com
www.Dorken.com
www.Huberwood.com
www.Prosoco.com
www.Viewrail.com
www.Rockwool.com
So basically, if your attic is conditioned, you need to actually condition it.
Perfect summary! Yes
😂
Bear with me on this one. So if yo insulate your attic with closed cell spray foam, you still need a dehumidifier, right? I bought a new build in New Orleans and the house is tight, but could be tighter... Thanks y'all!
@@buildshow q11+1¹1¹1
70 pints a hour, a day, I see its a 70H but what do you mean?
Always a great sign when Matt Risinger starts off with "we're going to get a little nerdy today"
I had the pleasure of meeting Joe back in 2004 at a conference and had lunch with him and just by chance I had my blue prints in my car, getting ready to build, and he was kind enough to look them over. I built an ICF home, metal roof with spray foam in the attic. 2000 square feet and only need a 2-ton unit, love it. Great guy.
What an honor to do an interview with Joe Lstiburek, he's my hero - having coffee with him would be like winning the lottery. Also, let's be honest, we were definitely expecting a lot more beard.
Lol my thoughts too. That is like my "weekend beard" 😆
As a sheet metal tech and duct installer in south Louisiana I can testify to the sweating duct with open soffit and gable vents. I've been making customers close those off for over ten years. If it's 100% humidity outside, it's 100% humidity in your attic. Attics used to be super hot during the day and it would take all night for it to cool down to dew point. They want to prolong the life of shingled roofs and keeping them cool does do that but it also makes a terrible environment for duct work if humidity is present.
As soon as I heard him start talking about us I googled "roof ridge diffusion vent" and his article was one of the first things that popped up lol.
Just insulate at the roof instead of the ceiling.
I'd really like to see a cross section of your roof because it's getting a little unruly to keep up with. Perhaps you could provide an axon-metric diagram?
I second that ... along with cross-section on his walls., eaves/overhang etc etc etc
I third that. This is to much for me, an up and coming builder.
How thick is the roof at this point?
@@ZNotFound I believe it to be over 1' lets see 4 inches of foam, I'm guessing a 10" rafter? then the thin layers of water proofing, and those stickers to raise the metal panel.
@@jayutley8748 yeah I studied architecture and i've lost track haha.
Incredible interview, Joe would get my vote for a Nobel prize. I’m currently renovating an old farm house built in 1950. I’ve spray foamed my underside roof with 2” of closed cell foam. I chose this method for another reason than to prevent the ping pong, that is too long to explain in this comment. But I’ve been worried about rotten roof sheathing since I had the foam sprayed in. Matt thanks for this valuable show you’re producing. Sure appreciate your devotion to doing it right.
Joe balances scientific rigor against real-world experience. He's competent working with formulas, algorithms, and models, but he's not doctrinaire about them (unlike many in the climate space). His approach is a lot more conducive to serendipitous discoveries. And he has a sense of humor. We need more real people like him in decision-making roles, and fewer of the autism-spectrum, narrow-minded technocrats who have risen to the top, like scum in a pond.
Don’t be so high on him. He’s much more confident and in love with himself than he is a person that is, you know, actually correct!
He’s been blasting off in-your-face talks for two decades and wrong half the time. That’s why this interview is awkward - Matt built his very own house off of Joe’s N-1 advice, and you can see he feels silly
Thanks Matt. I'm just about to finish my conditioned attic, so this video was at a perfect time for me. I will be installing a small dehumidifier and a circulating fan to keep the attic air moving. I'm old and not too worried about dying, so, if I'm still here in a few years, I'll let you know how it worked. Keep up the great, informative videos.
Any update on this? I'm curious about your experiment!
@@Shkrelic he died
I LOVE YOU JOE no matter what they say. Love you too Matt. This one was awesome. Good laughs. Great science. Great education. Thanks
I am a geothermal HVAC contractor and I do open cell spray foam encapsulation with open attic return air (no return air duct, drawing return directly from the attic). I use an ERV for fresh air makeup. I have had zero humidity issues.
Clear as mud. You're supplying dehumidified air to the attic, creating positive pressure. Then you have a fresh-air hole that you think will bring air in vs let air out. Where do you think the air pressure is going? I never heard any sort of organized, structured answers to the central questions raised here.
Dr Joe is a gift to humanity!!
I hope that you do more videos with Joe. I've watched everything that there is on him. And I want more.
You don't have to say we are getting nerdy. They are all a little nerdy, and PERFECT. Keep it up guys.
Most important part of the entire video, that I've learned from Spray Jones:
"Or, you could just use closed-cell and not worry about any of this"
The problem is closed cell is a full 5x the price of open cell per inch. So 5 inches of open cell foam is the same price as one inch of closed cell
@@jl9678 yes, but, you don't need 5 inches if doing CCSPF🤷♂️
@@DigitalBenny you'd need at least three inches which is the same as the price for 15 inches of open cell foam.
So do a mix to get the r value you want 2 in of closed and 3 or so of open. Which he also said in the video.
@@shannabolser9428 that's still 3x the cost of open cell foam. If you've got the money do it
Looks good. I never understood putting HVAC ductwork in unconditioned space, unless you're assuming (like we could in days past), that energy costs are ultra-cheap.
Thankfully in the semi-arid desert environment I'm in, high humidity isn't something to worry about. 55% interior humidity? Never happens.
Rockwool is great.
I would enjoy seeing a discussion, or maybe a series, highlighting and explaining some of the key differences in building from region to region
Agreed. I love matt, but i’m in CS4 and trying to learn what will work here in Missouri.
I just finished listening to dr Joseph. Great talk on vented vs non-vented.
LOVE his presentations. The Dr is in. This guy wish people could talk to him for every build we would never have issues. But people being cheap is why Manu time thing go wrong
Perfect timing again. I just bought a house and I'm already took all the spray in insulation out. And was thinking let's do spray foam afterwards. Now this ease my mind on it. Great content as always Matt.
We need more Joe!
Great interview Matt. Going to use that vapor diffusion port idea...
For Matt Risinger: I really appreciate you saying to read Joe's articles first. I did, it took me maybe 20 min or so and it made this video FAR MORE understandable with that context.
Thank you. I love your videos Matt and I love the "nerdy" details. Keep up the good work brother! The Lord Jesus bless you!
Very thankful for you Matt. Truly thankful. Building a track build home through a common luxury builder right now and you have given me an arsenal of information to stop poor building standards dead in their tracks. I almost would rather flip this home in Houston and get a custom build from you or one of your associates. I hope you find a way to spread your knowledge through the world of new build realtors, inspectors, and contractors. I have been surprised how many haven’t heard of you in Houston and I feel I can’t trust those who haven’t. I would almost say you should create your own standard because if you were to approve a material or builder or contractor people like me could hand over a blind trust throughout the build process and feel much better about our critical choices surrounding our biggest financial investments.
There is nothing like Joe it’s a talent to make science interesting and fun
I have a solution to this before you spray foam on new construction.
In my attic I installed a radiant barrier house wrap on the rafters from ridge to soffit.
Then had spray foam applied over it 2" thick of closed cell, this made it very tough and adheres well.
This allowed the soffit to vent as a normal roof to the ridge vents, which also cools the roof in summer heat.
The radiant barrier helps keep roof heating out of the foam insulation and as a first line vapor barrier.
almost 10 years now and have had no problems and the house stays cool for cheap in the summer.
The attic temps never get over 80F without any ducting venting into attic.
Thank you, I've been trying to figure out a vented solution for an upcoming build. What do you think of a couple solar powered roof vent fans to pull air through the soffit? I live in the South so it gets HOT in a vented roof during the summers
@@LincolnLog yea i guess, i'm no expert but solar vents are good but can clutter your roof. soffit and ridge vents are built in and work well enough. My home heats and cools well in Louisiana.
@@ClearWaterPumpWell Thank you. Do you mind sharing with me the brand radiant barrier you used? And I'm assuming they were stapled against 24" oc roof trusses?
@@LincolnLog My roof is not a were wide span only 28' at most over living. So my rafters are 2x6 with 2x4 ridge cross boards. I stapled it to the underside of 2x6 stretched across entire attic. From wall top I had to split 2x2 sheets to fill the gap in ceiling joists are 2x12. I left the ridge more open by stapling the foil to the cross boards rather than all the way to the point. It almost makes like a crawl space but saved me time and more foam. The foil was one sided and I faced the radiant foil side towards roof to reflect heat. It works as so much better than spraying foam directly on the roof. The roof will not heat the foam due to conducting but only from rafters. Then soffets can vent normally to ridge vents. In the corners on the hips I had to put a spacer block on the rafter bottom so air can flow in corner to reach the ridge. The hip roof normally ties in on corner rafter so not much room if you staple it tight. It helps to more less bend or curve around the hip corners, easier to staple.
The site I got my Radiant barrier from was : atticfoil.com/
Hope this helps! Thanks
@@ClearWaterPumpWell Thank you for the clear and detailed explanation. I copied it down and will apply the same principles to our home 🤠
all this to avoid the energy lost from ducts running through hot attics... makes me wonder if it wouldn't be better bang for your buck to just double-insulate your attic ducts and put a small amount of insulation outside of the sheeting to lower the solar gain. or, never put ducts in the attic in the first place.
Big thanks to Joe for pioneering building science. Great stuff!
This has made me super cheerful about my idea to include a dehumidifier draw from the loft when I set up my DIY (don’t hate me) clean air system.
I have a Chocolate Easter Bunny sitting on top of my HVAC unit in the attic. ICF home with Closed Cell on the roof deck. Always good for a laugh on tours.
Good old Joe, Great Show.
What about variable vapor throttles to prevent the humidity getting into the interior insulation in the first place? I reckon this dehumidifier is unnecessary if the air is well mixed and there's enough ACH up there. If you are going to have one, it doesn't need to be connected to the rest of the HVAC, just get a small one with duct right up in the ridge. Matt's clearly very well off, but the real art of building science is value engineering for durability. With enough money, of course you can do everything.
Great Interview! I really appreciate Joe's down to earth approach on a complex topic. This is also very timely for me as I'm in the depths of planning for an August build. Thanks for the great content.
Finally answered my questions about insulated attics. Thanks so much
I'd like to see more info and a drawing of the ventilation at the ridge discussed in this video. Thank you!
With the advent of Variable Speed A/C units...which stabilize and reduce humidity levels greatly as compared to conventional AC systems... it would be interesting to see if this issue is averted. This, of course, provided the attic space is actually conditioned via the system's supply and/or supply-return.
It was my biggest concern about our new home design, thanks for posting
Years ago I had a ridge beam crack, which wasn't discovered until, over the course of months, it was apparent that my roof was caving in. In the dry Colorado climate I kept humidifiers running in the house, and unbeknownst to me, there was humidity creeping up through the edges of the family room ceiling, which was part of a poorly redone garage conversion. Seeing your ridge line slowly cave in is not something you want to experience. It was an expensive repair, involving a team of people to figure out how best to fix it. Ultimately they brought in a giant jack and lifted the middle of the ridge back into roughly the place it should be. The problem was that the wood had warped and wouldn't just "bend" back into place, so this lifting, as you can imagine, torqued other areas of the roof.
I actually made a video about that:
ua-cam.com/video/fA0JkFxRxsk/v-deo.html
I'd be interested to get your take on what I did verses what your team did. It was definitely a difficult process and if I hadn't built a second story I don't know how I would have fixed the rafters, which had bowed and sunk as well as the ridge.
One of the best conversations I’ve heard. Great guys. God bless you.
Thanks for this video with Joe. I have been looking for this info for a long time. In my current house build and attic insulation has been a concern. This was perfect.
Easiest way to ensure you are safe is to install a dehumidifier in your attic and set it to 40%rh and just let it run.
Awesome interview. I've always liked your videos, but you go a bit light on the details and science for my taste. I like to really understand why things do or don't work. That said, I've seen you correctly recommend a lot of stuff that I have confirmed the details of through other sources, and now that I know how much Joe Lsbiturek influenced you as a builder, I know why!
and in cold areas you put a vapor barrier on the inside and vent the underside of the roof. So my place has this baffle that routes the air from the soffit vents to the ridge vent.
You had me going and then lost me when you said you had "pop it" exterior air inlets in an attic that you had gone to such trouble to seal. And Joe had said that you want vapor diffusion but not air as it only brings more moisture. So what is with the pressure differential open air vent? Good video always interesting when Dr. Joe is presenting.
Yeah I got lost right at that bit as well. It’s literally like having a soffit to allow moist air back in. That part didn’t make sense.
I wonder how hard the AC and heating systems have to work to compensate for the vapor diffusion membrane at the roof ridge. Appears this is the largest (always open) penetration in the home.
it just lets water out.
@@zhugeliang777 correct, however my question is not about moisture/vapor, apologies. I wonder if having a large, open-to-the-exterior, vapor diffusion membrane creates a large *thermal* problem -- seems the AC/heat units in the attic would be working around the clock to compensate.
Doesn't he have 4 inches of closed rigid foam on the outside. How is that going to allow vapor to escape from the ridge?
I have so many questions
It's all in the details, diffusion vent gives way for vapor to escape... Just don't block the vent...
Good question. IIRC he has two layers of Zip and ISO foam board in between. If you cut a port through all of those layers (and I don’t know if that’s the case)... it sure seems counter productive.
@@OHSCrifle Agreed. Matt's motto has been tight, tight, tight buildings and then he creates a breathable (not tight!) opening in his roof. I would think dehumidification and perhaps an attic vent/return would have been the answer.
19:21 “I also cut some slits...”
Thanks. I am actually designing a similar roof assembly like this and it helped a lot
I never really thought about this before. I'm looking at doing my first conditioned attic on a future house in Utah. Even though it's an arid climate, I will be adding humidity to the conditioned space with a Aprilaire 800 Steam Humidifier. Doing the moisture vent at the ridge, Zehnder Fresh Air Supply, and adding a small dehumidifier in the Attic; should solve my issues. Well at least I hope. Lol
I've had a closed cell spray foam conditioned attic for 22 years now and have not single sign of moisture, mold or rot. I just doubled checked after viewing this video. I do not have a dehumidifier.
I build my house in 2015 using open cell foam, I remember reading the Cool Hand Luke article, as I was reading everything related to building science during that time. I have often wondered if there was a concern with rot on the roof deck side of the foam. How would one go about measuring/knowing when the duct work is leaking "enough" or the correct amount of humidification has been added? I really appreciate your show- love it when you get nerdy.
you could buy a wireless temp/humidity sensor with logging. you'll be able to see just how humid it is up there.
Could you install an extra return vent from an ERV or HRV at the top of the attic? That would suck out the humid air, right?
Very useful - thanks for the nerdy links!
Dorken blocks VPN users so I'll look for a better vendor, but it's a great start.
In finland it's in the code that between the tiles/metalsheets etc. and the roof there has to be atleast 2" of breathing room.
I assumed the problem with the vapor drive from the conditioned attic space is when it condenses on the underside of the sheathing. You guys (in cold climates) will have most of the insulation on the outside of the roof deck/structural sheathing, but you'll still need sheathing to support your cladding system above this exterior continuous insulation. OSB also has low perm ratings so vapor will find it difficult to migrate across this, or even plywood. This will limit the drying potential due to the reduced heat flow across the enclosure, and you therefore need to maximize the ventilation and drying potential from above.
@@FrankReif images.app.goo.gl/PMSVJ6aAzGjEqnW6A this is really usual roofing system here if the picture opens from this link
i v put domestic hot water heat pump in the attic; its always hot there so it runs efficient, it dehumidifies the attic, cold air is directed to my pantry, during summer when i send hot water down the drain i passively remove heat energy form the house
AWESOME MATT!!!! I geek out on the HVAC stuff too... Im an Electrician by trade...HVAC/INSULATION geek by night!!!!
Thanks again Matt, I miss Summer Camp too. Stay safe
There is talk about vapor diffusion port in Alaska but I recently read it is only suitable for climate zones 1-3. What is the issue with the vapor diffusion port in colder climates?
good question.
So, we have to redo our roof, roof decking, and ceiling insulation in our house. I was going to do zip panels, with zip peel and stick underlayment, and then do metal roofing directly on top of that. I was hoping not to do wood spacers between the decking/underlayment and the metal roofing in hopes of saving money, to prevent birds from getting up in there, and to prevent wind from getting under it during serious wind events. I was also hoping to take out the ceiling insulation in the attic which is covering all of the electric (which were going to have to work on in the future), and to get all the mice out of there. Plus the HVAC is in the attic and the attic space gets incredibly hot. So I wanted to switch to an unvented roof, and use either rock wool insulation or fiber glass insulation in the roof rafters under the decking (we can't do spray foam due to an allergy). To do all of that would be tough to swing financially, even with me doing all of it myself. So it's hard to think about also doing wooden spacers between decking and roof, additional insulation above the decking, or hunter panels, venting system behind the insulation in the roof rafters, etc. Is my game plane, reasonable/safe? I've consulted 3 roofing companies, and they all said different things... So pretty confusing....
BSI-088: Venting Vapor
Joseph Lstiburek
Sometimes the obvious is not so obvious. And sometimes, the not-so-obvious becomes obvious. For example, installing leaky ductwork1 in a vented attic is a pretty dumb idea. It leads to negative pressures and high air change that depending on the time of year and climate zone, results in part load humidity problems, ice damming, excessive energy use, loss of comfort, whatever. If radon were valuable, we would mine it this way. Where there is an attached garage, we call it the Kevorkian option. Everyone pretty much gets it.
Amazing content. Keep all this nerdy stuff coming.
@Matt Risinger - I am in the process of finishing up a new home build for myself here in Texas and went with open cell foam on the underside of the roof deck in my unvented attic. I worked through the potential humidity problem in the attic by adding a small HVAC air return intake duct that draws air in from the attic and set up a supply vent that feeds conditioned air back into the attic. It seems to all work extremely well and the relative humidity in the attic stays around 50%. After watching this video though, I think maybe I should be drawing the attic return air from as high up at the peak as I can get. I have been monitoring the attic RH in the breathing zone of the attic and not up near the peak. I think I will move my humidity sensor higher up at the peak and see if the humidity is higher further up. What do you think?
Matt, I loved this video. So much better than the totally paid for product placement videos. There should be plenty of companies that'll sponsor you for just ad spots rather than the full sales videos.
Matt, I'm right around the corner from you (essentially a neighbor). Have been a fan of the Build Show for a while. I'd love to bring some beers and get a tour of the house before you move in. I found you mostly because I did a kitchen remodel last year..... But really appreciate your videos and knowledge. Keep up the great work man. Your house looks BOMBER!
Just walk over there with some beer and a Rockwool t-shirt. He'll let ya in 🙂
I sure would like to see various detailed sections of the various options. You could do this or that, show me some detail drawings with the options please.
Man, you did geek out. And man, I loved it! What a fascinating topic. Thanks Matt!
Why not have a vent in the conditioned attic with a whole home dehumidifier? Why should it be any different than any other room in the house?
I could never find a straight answer on that but I think the idea is that duct work is so leaky that it would work just fine. There are conditioned basements that are similar to the attic if you think about it so why not have a supply and return duct. They mention a supply duct in this video.
It wouldn't be different if you have a return duct, or a supply duct in the attic, but most homes do not and code may not allow it depending on what materials are exposed in the attic space. Without the circulation, humidity rises to the peak and starts moving into any vapor open materials.
This was great information, but i feel like the part that wasnt emphasized enough was the hydro-buoyancy that Joe mentioned. Sounds like that is the fundamental reason why attics that are included in the air envelope can have issues with higher humidity. Glad there is an easy enough solution with the addition of air supply/intake in the attic or a dehumidifier. I still don't understand how the difference between open cell and closed cell foam is relevant here. How does the type of attic insulation affect how moisture is building up in the attic?
Open cell is vapor permeable where closed cell achieves a vapor barrier. With the vapor permeable insulation installed at the roof deck, they wanted to allow defusing to stop the ridge rot. Closed cell would not allow the vapor to reach the roof sheathing and can be addressed in the attic space.
Please explain the 1/150 venting application in code recommendation. I did not get that. Also across ridge in conditioned space in attic; what if you added a 16 ply plastic sheet sealed on all edges with tape to capture any vapor that was buoyant enough to reach ridge. I would still add dehumidifiers to address and control moisture. Love the 75 degrees for storage.
Thank you!
In all the clever and advanced conditioned attic scenarios, we get back to this: a properly vented conventional attic solves a lot of problems, is cheap, and has been done for decades. Old timers knew what they were doing. They operated on KISS principles and created solid, affordable housing for decades. If we need some storage space or a hideaway a conditioned attic might add, stick a shed in the backyard and throw some insulation in it.
My experience with open cell. I've had a ducted dehumidifier set at 50% since building the house 15 years ago. Attic has always gotten warm and moist especially at the crown. Tried 6" supply and return in the attic; very little difference. Tried pulling air constant at 100cfm from crown down into living space (against code but wanted to know) and that did nothing but make the lower living space warmer. Tried pushing air from below into attic constant at same 100cfm and no change. The temperature and humidity in attic were beautiful from morning until about 1-2pm. Got better then about 10 hours later so it was definitely from the roof deck heating up. Decided to just put a dedicated dehumidifier in attic right next to the existing one. Free standing and it turns on around 1-2 pm and runs for 3-4 hours. Takes humidity down to 54%. Temperature still higher (around 83-86) but humidity much better now and I'm not worried about potential rot anymore. Hate having another dehumidifier but I know it will turn on when the conditions up there require it and when the moisture is in the air and not locked up in the wood or foam.
BTW, I live in east central FL; very warm and humid.
I am really struggling with this: what's the right way to retrofit an 80+ year old attic space to modern specs, but SAFELY so it still lasts another 80 years. prioritizing longevity over maximum efficiency.
are there ducts in the attic? if not, insulate the ceiling and leave the attic ventilated. if so, take the minor efficiency hit on your HVAC and insulate your ducts, insulate your ceiling, and leave the space ventilated.
also, as someone with a very old house, don't underestimate the power of zoned HVAC. last summer I finally got mini-splits to every room. in the winter, I was able to turn the gas boiler way down and adjust the mini-splits based on which rooms I was using at the time. I was more comfortable and cut my heating bill in half. even though natural gas is about half the cost per unit energy, the fact that the mini-splits were only heating the rooms I was in meant overall way less energy used. no more heating every room in my house while I slept. long story short, if you have one or two occupied rooms at night, it might make sense to put in a couple of mini-splits or even window ac units during the summer.
I repair appliances in people's basements a LOT. It is VERY common to see a simple dehumidifier stuck in the corner of a 1500sf concrete wall and floor basement here in Massachusetts. I have been saying for 40 years to people in this crazy damp environment...get a big fan... ir a couple of fans...and get ALL THE AIR over to the humidifier. Dont forget...they cant imagine having one in each corner. It solves all the issues with wet surfaces that migrate. You need a rotating pedestal fan and dehumidification in your attic. And I bet ONLY that. Problem solved for $300.
Great guest , brilliant guy
this sounds like a good idea regardless of insulation strategy.
Finally a builder who cares. I have been sharing these articles
“Cool Hand Luke”
And Ping Pong
With builders, HVAC and foam guys we have dealt with over four or five years and they just didn’t get it. Currently finishing our current home out and we went with whole home dehumidifier and also a supply and return in the conditioned attic. But don’t forget to have the HVAC guys install a smoke detector in the main Air handler to shut down the AC unit in the event of a fire in the attic space. Great video guys!!
I am very happy that I have learned from Matt and Joe to create an enclosed sealed space for my house and my mechanical equipment. I thought that this was simple and sensible. Simple and sensible has now become a technical mess fraught with danger. I challenge you to propose a simple plan to make this work in a 2 minute video otherwise people are going to stop listening to you guys.
that is Matt in a nutshell; always using the newest gadget to try to wring out the last bit of on-paper efficiency while not considering either design changes (like no ducts in the attic at all), or time for return on investment. I can't blame him too much; people tune in to see the new gadgets and trends.
I’d say the small dehumidifier, dedicated to the attic, is the easiest solution.
I must admit, I’m excited to watch this.
So again, what do it need to do if I have vented attic now that I want to convert? Contractor said do 2 inches of closed cell then do open cell and close all vents. Also remove all existing ceiling insulation.
So, above the roof rafters is ply board, then water proof zip sheeting, then two staggered layers of insulation where you cut some vent slots, then another zip layer but a permeable membrane over the slots, then wooden battens under the metal sheet roofing. My question is, how does the vapours from inside the attic go through the plywood, water proof zip sheeting and then to the permeable membrane before evaporating out?
Although it's not immediately apparent, and even seems a bit illogical or counter-intuitive at first glance, digging deeper into the details and peeling back the layers of the onion (namely, the roofing layers), as it were, reveals that Risinger's vapor diffusion port should actually work as designed and intended.
By the way, it's clear, from 19:23 to 19:30 in the video, that Risinger cut the vapor diffusion slit *only* in the top Zip sheathing layer, and *not* through to any of the layers beneath that; namely, he did *not* cut the vapor diffusion slit in the two polyiso board layers underneath nor in the first Zip sheathing layer underneath the two polyiso board layers.
But ... furthermore ... it's also evident that Risinger did *NOT* need to cut any slit at all! He did *NOT* need to cut that slit in the top Zip sheathing layer, which was totally unneccesary, and I think somewhat ill-advised and not such a good idea, IMHO.
Here is the roofing layer assembly (from the ridge to 2 feet down from the ridge), starting from the bottom/inside and working up to the top/outside ...
Layer #1: Rockwool R30 batts sandwiched between 2'x8' LVL rafters on 24" centers. The Rockwool batts are vapor permeable.
Layer #2: Zip sheathing. This first Zip sheathing layer is taped and sealed to the house's exterior wall Zip sheathing that comes up from the foundation, for a continuous air-tight and water-tight weather-resistant barrier sealing of the entire house, without any breaks, in Risinger's "monopoly framing"/Lstiburek's "perfect wall" concept. The Zip sheathing is an air-tight and water-tight weather barrier, but it is vapor permeable. Risinger states this in another one of his videos, and Huber states this on their website ("the integrated protective overlay of a ZIP System wall sheathing panel is permeable to allow for drying to the outside").
Layers #3 and #4: Two layers of Atlas EnergyShield CGF (Coated Glass Facers) 2" polyiso insulation 4'x8' boards, oriented perpendicular to each other with offset seams. Atlas states on their website that these EnergyShield CGF polyiso boards are vapor permeable.
Layer #5: A second Zip sheathing layer.
Layer #6: Delta Foxx vapor permeable roof underlayment.
Layer #7: 1"x4" battens/furring strips, to create a 1" air gap, for venting the roof.
Layer #8: Standing seam metal roof panels.
Layers 1 through 6 are all vapor permeable, all the way up to the 1" air gap roof venting system at Layer #7. That's exactly what's needed, and all that's needed, for the vapor diffusion port. Risinger didn't need to cut that slit in the top Zip sheathing layer (Layer #5), because it's already vapor permeable.
@@charleswhalen7332 thanks for the reply. I am guessing that it'll also depend on the weather zone that the house is built in. For really cold weather environment, there will be more vapour to manage. Cutting slots at the top seem to go against the thermal bridging he was trying the achieve. Awesome house though.
@@lozza2272 Lozza - Very important point and distinction regarding the relevancy of and dependency on the particular climate. In watching these many “Build Show” videos, I’ve noticed a big difference in that regard between Matt Risinger on the one hand and Steve Baczek on the other hand. Although Risinger apparently did build in colder climates earlier in his career (Portland Oregon and the Washington DC area, I believe he’s mentioned), it seems that in the last 20 or so years he has only built in Texas, a hot climate. Although Baczek apparently has designed some houses in Arizona, all of the videos I’ve seen of his houses have been in climates with colder winters, mostly in Massachusetts and one in Columbia, Missouri.
Now to the point of the difference between the two of them. For all of Risinger’s houses he builds, he always does closed, sealed, conditioned attics. For every one of Baczek’s houses that I’ve seen on video, he always does open, vented attics. I gather that the salient reason for this difference is the serious problem of ice dams that come with closed, sealed, conditioned attics in places where there is a substantial amount of snow in the winter. I have also heard Dr. Joe Lstiburek discuss this problem. So apparently, for that reason (namely, ice dams), I gather that it’s not advisable to do closed, sealed, conditioned attics in cold climates, and really just isn’t done.
Having a vented attic alleviates the problem of vapor build-up in the attic and associated ridge rot, as vapor can easily escape through the attic’s ridge and/or gable vents. So it would seem that this is really more just a problem associated with closed, sealed, conditioned attics in hot climates.
I love these deep dives
If a vapor permeable/impermeable roof membrane doesn’t really matter, but moisture can collect in the ridge areas, then why doesn’t a vapor permeable membrane not help in those ridge areas?
Matt, could you have put a more standard all in one heat pump water-heater in your attic to act as a dehumidifier? Kind of a two in one solution. Thanks
Personally, I think putting a hot water heater at the highest point of the house would be a risky proposition... A leak would be pretty bad.
Well he does try to explain it but not very well. During the day/night cycle air expands and contracts. Air has a density of 28.6 grams per 22.4 liters at STP whereas the equivalent density of gaseous water is 18.01 grams per 22.4 liters at STP. But pure water vapor at STP is a weak vacuum waiting to happen. But Air can support a small amount of water at STP and makes it trivially lighter, which will rise. But the phenomena of ping pong is only partially due to this during the hottest part of the day the most exposed parts of the attic heat up and cool off the air expands, but it’s not until the heat gets high enough that vapor production maxes out, the more embedded vapor the longer it takes to heat up and the hotter it will be when the last molecule gets vaporized. Which means the sun is higher. So now you have vapor/air mixture that is trivially lighter because of the water, but much warmer because of the heat. This is going to rise in the open cell foam and as the sheathing cools at night, faster than the house it’s going to reprecipitate on the coldest part, the sheathing. Again in stepping up the moisture content is higher, it takes more heating to get it vaporized ( because as local, in foam vapor pressure rises, it makes it difficult for more water to vaporize at a given pressure). So at each step to get the vapor mobile it needs to be hotter, have more water vapor in the air, and it will rise faster. Essentially you are forming a big cloud in the foam sheeting of the attic at the end of the day, but no rain.
I mean I live in houston, we know we teeter on the edge of wood rot no matter what you do. Mold is just everywhere. But the idea of closing an attic to air flow bugged me for the exact reason he mentions on the website. In Houston keeping moisture out is a big problem because nighttime humidities are frequently near saturation, and we can goes days, often weeks without appreciable sunshine. And on top of that roofs leak, often not enough to do damage but just enough to add moisture. The satellite people come out, they punch 4 holes in the roof, windstorms blow water up the shingles, tar paper shrinks and tears, gutters overflow with leaf fill and wind can blow the water into the soffits, AC condensate leaks, the condensate lines themselves condense moisture.
I like the idea of ridge vents, yes they are a source of potential moisture, but they create a nice laminar airflow that keeps the attic cooler while on sunny days driving that moist air out with warm, but not hot air.
No Joseph, I like you, anyone who is fighting the moisture problem is my friend. I can’t pop an exterior wall nowadays without have the irritating black mold slamming into my nostrils.
Nerdy discussion indeed! And this comment from a non-home builder (but a dedicated DIYer!)
He finally realized spray foam at the ridge was not the best set up
So if you reccomended conditioned attic
Now you have moisture accummulating at ridge
I insist , vented attic is best, place ac duct work under the attic inside house conditioned space
Dr States clearly vented attic spaces are best
Rockwool is amazing, Matt's attic is acoustically friendly.
Love the show and have been using many of your build techniques and endorsed products. .
I need to watch this one more time. I feel like I need a summery or quick review.
House I'm building in DE has ridge vent and vented soffit. I've been considering switching to a sealed attic and that's why I'm researching and watching videos.
I prefer to keep the ridge and soffit vent open but there are pros and cons to both. Being a shore home I wonder if a sealed roof system is more likely to stay together in high winds.
Can I use this diffusion port in Zone 4marine? Joe says "The diffusion port approach is limited to IECC Climate Zones 1, 2 and 3. It SHOULD NOT be used in colder climate zones" (- BSI-119: Conditioned Unconditioned November 15, 2020.) In 2015 BSI-088 Joe said "maybe zone 4 could be added soon". Apparently that has not happened. Apparently you can also use this method to remedy a problem in old construction (in zone 4 on up) but not in new construction. So they used it in Alaska SIPS repair.. But what are they doing in new SIPS construction in Alaska? The 2021 IBC still says "The port area shall be greater than or equal to 1 / 600 of the ceiling area" instead of 1/150 as Joe states here... It is hard to keep up with all of this when the latest BS (Building Science) is changing faster than new information can travel. The use of diffusion ports in Matt Risinger's home is similar to the solution to the Alaska SIPS problem. The polyiso layers shrink a bit and create air channels in the middle of the sandwich. Then moisture accumulates at the ridge via hygric buoyancy. Why can't I use this method outside of zone 1,2,3? If not this, then what method can I(we) use to disperse the moisture that will rise up to the peaks?
good question.
I thought the solution was to exploit the T difference and use a small automatic fan to circulate air from beneath the drywall ceiling to above this pulling the moisture into the HVAC cycled air. The question really is when will we seal the insulation away against the rafters(or trusses) and then build ventimg in the cosmetic drywall layer between the attic and occupied house? BTW, i like the batts instead of foam which will alow water migration IF the roof ever leaks and can be removed and replaced for any repairs or modifications. That alone does so much because you arent creating a hot zone hotter than outside even. Some moisture is fine in reality, there are countless attics with just ridge/soffit vents that work without rot. Dial that back to include houses that had turbine vents before that and even just gable vents before that!! We have a house in FL that was built in 1937 and it has had ALL THREE over the years and the only repairs made in the 1x4 and 1x6 decking were made from regular roof leaks.
So what did we learn. That sealing up the attic, rots the roof ridge( attic wood) cause more or less problems. Dehumidifier or just vent the attic and not have to worry if the house and roof will rot by the time you die. This spray foam might be the devil in disguise. May help ac systems and air quality but may kill the house in the process. Im i missing something???
So after all that effort to seal your home U unsealed it? It seems like you would have been better off to dedicate an actual dehumidifier or a couple of them to your system for your attics. I understand some of the makeup air ports but if your happy with your system prior to opening up the ridge, why wouldn't you just work on strictly dehumidifying the attic while putting closed cell spray foam at the roof line?
Same question
My question, a bit off topic, BUT - the recent house we built called for closed cell spray foam against the roof sheathing and then unfaced batts for about R60, with NO VENTILATION !
no 1" air gap with ridge vent, etc. ( a cathedral ceiling - 12/12 )...The building inspector said the dew point was controlled, but that meant more to me about condensation than how damn HOT !
those roof shingles are gonna get. Thoughts, experience, etc.....?
@@robertswaine6096 his engineering deferred to the shingle manufacturer for any warranty issues...I live in Seattle. it never gets very hot except for a couple of weeks in July-August, but my roofer stops when his shoes start melting into the asphalt base, so I know those shingles are like bacon frying on a hot pan, and the edges start to curl up.
Matt R. is using "hunter panels" to create air space above his sheathing - I'm assuming because there is a heat build problem, with spray foam underneath. Thanks for the link, Robert.
Is there a video that shows the roof In process? How much sheathing is removed? What are 1x4’s attached to at the ridge, etc?
Your vapor defusing port doesn't effect your blower door numbers,also putting a port in your ultra-air supply will effect your vent leakage #s correct.??
One of the old thoughts on the reason for venting your attic was to prevent ice dams in the winter, and to help reduce the temperature of the shingle so that they would last longer. Question... Does using clothes sell spray foam on the other side of your roof deck cause your shingles to live a hotter life and therefore shorter life?
Do we need to incorporate a secondary roof deck with some ventilation underneath it to cool the shingles? Matt showed this with the diagonal perlons he put in for his bulletproof metal roof...
I'm wondering if there'd be benefit to doing this for a shingle roof with a second layer of sheathing on perlons....
I love this guy.
Can I rent your attic for office space? I still down understand the very best hack-- using blown in-- to keep the juices out, except 2lb foam; but I don't want to use foam. Newspapers and Rocks with 2lb at the seams.
But I do love the idea of another portable 7 gallon Dehumidifier with pump line that I can monitor from time to time. I have a GE in a FL condo and it's my favorite piece of tech ever. It turns my FL indoors to Arizona dry.
@risinger - where can you purchase the dorken product you used on the roof? The link in your description does not work.
Excellent stuff
Matt, you are one of my faves to watch, your education of us is max, 68 years old, carried bricks for mom at 2, and she mixed all the mortar, by hand in. a wheelbarrow, my brother and I shoveled into a trailer at the creek, My brother and I have been restoring 1800 log hand hewn homes, and I while living in Seattle, designed, Built Hand Peeled,-scribed Swedish cope log Homes, even spent 3 years in Japan Building late 80s early 90s, Granddad always said if you are not learning something every day, your not paying attention! My question is on. your attics, do you have an estimate of cost Per Sq Ft and a ratio to savings overall, Thanks for the ride!!
While fully appreciative of the advancement of building science, I long for some low tech solutions.
LOL. With you brother! I remember living in Houston with only a ceiling-mounted whole house vent fan to the attic, with all windows open. As a kid I didnt care, but now as an adult, insane.