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Community and Q&A

Roof Insulation R-Values in IRC 2024

jollygreenshortguy | Posted in Building Code Questions on

Does anyone have the “inside dope” on IRC 2024 code changes? The 2021 version upped roof insulation values from R49 to R60 for zones 4-8.
I’ve read in “unofficial sources” that the 2024 code will be reducing roof insulation values again. But I don’t know how much.
Do any of you have information on that score that you can share?
Thanks a bunch!

edit – Never mind. I found the answer. They’ll be going back to the 2018 values. It’s on

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  1. Expert Member
    BILL WICHERS | | #1

    If they go back, that's a good thing. Going from R49 to R60 really doesn't save much additional energy, and while I haven't run numbers, I'd be surprised if the additional energy savings would EVER pay for the extra insulation. I wish they'd take basement insulation back to R10 from the now-required R15 too, for the same reason.

    When the energy codes go too far towards the "save every bit of energy we can" side of things, it only serves to drive up the costs of houses, which makes it more difficult for people to afford the homes in the first place. IMHO, it's better to go after things that make a bigger difference, like the new requirements in some areas for blower door testing and air tightness standards.


    1. Patrick_OSullivan | | #2

      I agree. Looks like wall requirements are staying the same, and while it's not the end of the world, I have seen how that increase has had unintended consequences too.

      In my part of NJ, *no one* puts exterior rigid foam on houses, so when faced with a code requirement for R-20 + R-5 continuous or R-30 cavity, they're filling 2x6 bays with closed cell spray foam to hit R-30. Not only are they probably not getting to R-30 (because of having to underfill with closed cell), this cost is then just getting passed on to the homeowner. Going from R-21 with fiberglass to R-30 with closed cell is a very non-linear jump in cost, and in our climate likely does not make sense on an economic basis alone.

      Meanwhile, we have air tightness requirements but no testing happening.

      1. kiwiscott | | #5

        I’m in Northern NJ and a contractor is saying spray foam 2x6 walls and 2x12 rafters is the easiest way to get compliant.

        What I want is Zip R on the exterior for the air tightness on walls and someone to help me with the roof.

        Everything here feels cost prohibitive

      2. jollygreenshortguy | | #8

        It's a pity about the spray foam. Closed cell spray foam is one of the worst insulation choices as far as the environment, being near top of the list for embodied carbon.
        So codes intended to make homes more energy efficient are pushing people towards higher carbon materials.
        Talk about losing sight of the goal!

    2. Expert Member
      DCcontrarian | | #7

      What's so bad about R15 in the basement? Even with R10 you're probably going to do 2x4 studs, why not fill them?

  2. Ryan_SLC | | #3

    I do think it unfortunately, but 100% building science has not driven the market. This has been a completely frustrating experience for me to want to be as green as possible, and it's frankly proving not worth it.

    I know in my large city area, no local normal consumer store (Lowes/Homedepot) or even lumber yard caries a single bag (not pallet) of high density cathedral batts or Rockwool. None. Even then, furring is nearly required. While furring might be allowed, it's not a building strategy. It's an after thought to something else.

    I can't even imagine the proportion of 2x4 framed homes in my area. It's probably most.

    On top of it, no offense, but then I read about wood burning heat in homes on GBA...and I about give up hope. I don't think updating a small addition on my 1980s home to R49 with a high efficient furnace for the remainder 3,000 sq all in probably crud R19 will make the green impact, but it's sure proven to be nearly impossible to get to.

    Or you see that the gas stove industry hired the exact companies Tobacco used, which turned out to be the largest lawsuit in US history?

    It's been disheartening to see lack of product options.

    1. Expert Member
      BILL WICHERS | | #4

      Lowes typically carries Rockwoll brand mineral wool, usually in several sizes. Home Depot used to carry Owens Corning's Thermafiber brand mineral wool batts (which I like), but those have gotten more difficult to find since the pandemic for whatever reason. My local Menards carries Johns Manville brand mineral wool batts in several sizes, which seem to be the value leader at the moment. My local Menards also carries some high density fiberglass batts, but not much -- high density fiberglass is less common from what I've seen. The commercial supply houses should be able to get you whatever you need.

      There are lots of old structures around built to earlier standards. That's nothing to get depressed about, you can't hold the past to present standards. It's even possible today to build 2x4 framed houses that perform very well, by using exterior rigid foam. That's actually my preference in terms of insulation, although I do prefer the more solid-feeling wall you get with 2x6s on the exterior.

      Any improvement you make helps. Going from an 80% to a 95+% efficient gas furnace is still cutting down on your fuel use by 15+%.

      The "gas stove" issue is a manufactured problem. The people pushing that are pretty shady if you look into them. There has been an issue with politics mixing in with the "science" in too many cases. Some of that is where excessive code requirements come from too, since people get overly focused on a particular small part of a problem, and often make the big picture issues worse as a result. I have posted on here before about how going "all electric" can actually INCREASE your overall emissions in many areas, due to power transmission and energy conversion losses throughout the system.

      There are other "issues" out there that are really just trying to push people to buy things too. I was, for example, recently reading an article written by the NRDC about transmission line losses. They were pushing fancy new carbon fiber reinforced wires, instead of the ACSR (Aluminum Conductor Steel Reinforced) wires commonly used. I'm sure the carbon fiber supported wire -- which still uses aluminum as the conductor -- is more expensive than the ACSR stuff. The article was pushing these new wires as an efficiency upgrade, but looking at it from an engineering perspective (I'm an EE), it becomes clear that ALL of the efficiency gains they were talking about were coming from.... Using a wire with more aluminum in it. A bigger ACSR conductor would accomplish exactly the same energy "savings" as the fancy wire, but likely at much lower cost. They then played around with some numbers to make it sound like this line loss issue was a huge deal, but it's not -- typical transmission lines are already usually designed to be 94+% efficient. The very large transformers on the ends get way up over 99% efficient. There just isn't much savings to be gained there, but there is plenty to spend money on. That's not being green, that's "greenwashing", and it's a Bad Thing.


    2. Expert Member
      MALCOLM TAYLOR | | #6


      "On top of it, no offense, but then I read about wood burning heat in homes on GBA...and I about give up hope."

      Why is that?

      1. Ryan_SLC | | #9

        Certianly sounded spicy, but hear me out.

        In order to accomplish code on a simple addition where non of the rest of my house is close to current code, and never will be, structural non required rafters were furred down. So building science has now stepped on structural science.

        Furring is about the crappiest wood you can buy. But now my entire ceiling holding up heavy rock above my head is not structurally required but is connected to the most twisty crap imaginable. Probably the only bay of crappier wood you randomly could select from is 1x1. But with massive screws, we accept it. Okay. Fine.

        As said before, in Salt Lake area, with 3 million people, not a single Lowes or Home Depot or lumber yard I've called carries a single bag batt bag of R39C, R30C, or Rockwool R23. So now I HAVE to foam. To order R30C, R38C, or Rockwool in an amount to get to R38, I have to pay more than spray foam. No questions asked. It's now impossible for me to meet code without buying a pallet of insulation. Impossible. Even online, I can't have it shipped to me, no matter freight cost. What other building material is so elusive or exclusive? Now my only solution is a product that professional company says "no living or breathing" thing in the house for 24 hours. Are we green yet?

        So what has code for efficiency done for me or my world where I actively want to be gree? I added a 100 sq ft addition, but the amount of non structural change and material just to meet ceiling code is not actually going to make the difference because it touches a massively larger roof line that is more than likely R19 at a neighborhood of R19 at best.

        But in SLC, where the air can be the worst in the country for PM2.5 in the winter, we know wood stove burning contributes massively to PM2.5. To control our purple non green air, we require days where wood stoves are illegal to operate. It's not theoretical when living in a valley bowl.

        So, wrapping it back. Does my R49 or cheating R38 100 sq ft addition improve the world where I live when high efficient furnaces are standard?

        I'm not blaming a group, this site, people trying to improve the world, or anyone for it. Lots of huge help on this site. It's help getting to code. No one is debating purpose. Fair...

        Yet. I can't buy material in a major city to meet code, or have to go beyond structural purpose...building "science" and material are almost at 100% non speaking terms in reality. None. If we're talking actually green...the standards of insulation causing this much stress while PM2.5 dumping wood stoves are just accepted because they are accepted... It's a It feels like an injustice to the entire purpose of slapping up 2" of foam, spraying the air with 2 part closed foam...It's difficult.

        In my limited time here, I've not seen anyone pretending to ask how to reach R60. So building science might be right on insulation, but it's just failing reality in current code. I'm not being a fatalist. But if building science wanted to accomplish going green...send all the money people will spend to go from R49 to R60 to retrofitting every single home with a wood stove. We've accomplished more green, created less waste, created less material junk....that's something! Slapping up unholy levels of foam? Seems a bit like advocating for foam producers while waiting for real insulation materials to come to market.

        1. Expert Member
          BILL WICHERS | | #11

          Looks like you're getting some unfortunate first-hand experience in what I've often pointed out here, where well-intentioned code requirements can actually cause more problems than they solve. You're right about the insulation in your small addition -- it won't make a huge difference in terms of overall energy efficiency. You'd gain more from putting in a higher efficiency furnace than you will from putting in R49 over R30 in approx 100 sq ft of space.

          I did look at two Lowes stores in Salt Lake City, and it looks like Lowes in your area doesn't carry as much mineral wool as they do in my area. That's surprising to me, I would have thought they'd be more consistent nationally, but apparently not. Regarding the facer though, mineral wool usually comes un-faced. I would just order some MemBrain and put that over the assembly after all the batts are up if you need a vapor retarder.

          Wood stoves are something of a conundrum of greeness. Many people who use them can fuel them with deadwood and other "scrap" from their own land. This is "green" in that it is using something of a renewable resource, but is not green in terms of emissions -- and wood burning stoves put out some nasty stuff. It's not just about "carbon" emissions. There are MUCH WORSE things to worry about that come from combustion of many materials. You end up with a trade off: locally source, renewable fuel, or much less emissions of nasty stuff using propane or natural gas. Either can be "green", but for different reasons.

          This is the big issue, and why I always tell people they need to consider the overall system, the big picture, and not focus on any one small part of it. Off in the rural frozen North, with only a few houses per square mile, a wood stove might be more "green" than a propane fired furnace. In such an area, fuel issues are a priority over emissions issues. In your area, where the emissions would tend to collect in the value and contribute to high particulate levels, emissions would be a priority over fuel, and natural gas would be better. You could go with a heat pump too, but remember that that usually means you moved the emissions somewhere else -- but that might, in your case, mean the emissions were moved out of the valley, so still a plus for your locale.

          I do find it's common for people to way oversimplify things when it comes to concerns about "being green". The big one I usually see is people thinking that going "all electric" is "green", when the reality is "sometimes". It's entirely possible, and even likely in some cases (like using electric resistance water heaters in most areas), to result in MORE emissions than burning the fuel directly. This is because of system and conversion losses that most people don't really understand, don't consider, or are simply completely unaware of. This is an example of a push to "be green" that can actually make things worse. Other issues, like your "wood stove in a valley" example, show that what is the best option in one area might not be in another, so one-size-fits-all solutions, which are usually what go into the code, often cause problems in some cases.

          BTW, spray foam at least is stable once it's installed. It might not be the greenest at installation, but over time it's not a problem. Also, twisting and bad-looking furring lumber is usually fine structurally. Appearances don't always mean strength is compromised. Remember that most "graded" lumber is VISUALLY graded -- someone eyeballed it and says "looks like No 2!" basically.


          1. Ryan_SLC | | #12

            I wouldn't even counter argue points, because I do realize there can be difference of opinion. Arguing a person in a small area with wood stove, okay. Agree. But code gives not a fig to Salt Lake, Purple air leader sometimes of the world...wood stoves are allowed. The Great Salt Lake is a toxic human killing disaster that is drying up. But wood stoves are not disallowed. What in the world? But I HAVE to put up R49 on a 1980s home that will 100% be torn down before anyone retrofits the insulation. That's not only bonkers, that's almost inexcusable promoting single solution companies.

            One thing we agree on, Rockwool, Thermafiber, and Cathedral insulation does not exist in a single non pallet level amount in Utah, even through a lumber yard to reach even R39. R49? Not a chance. But I agree on the intent. I want better insulation and efficiency.

            So...building science has utterly failed a millennial that wants to do right by efficiency. Therefore, I can't even imagine the outright non compliance that is intentional by big builders in my area. I know they can't meet it, because I can't meet it. There is no remedy but foam. What would someone in a rural area do with no spray foam options?

            But code, on efficiency, is silent to wood burning in worst are in the world at times.

            It's a bit off. It's certainly destructive to intent.

          2. freyr_design | | #18

            Well, let’s start by saying that code is something that is meant to be a basic framework that local authorities can adapt to their areas. I think you are basically saying your local government is failing you and not the irc. The irc doesn’t care about Salt Lake City, it cares about regions and climates. Also there are requirements in the code for wood burning stoves, they have to be epa rated (at least in CA code, haven’t looked at irc specifically for this).

            As to the rafters, this seems more like a design issue. There are many things in a house that are included that have nothing to do with structure, for example 2x4 wall are generally structurally sound yet are not used because they cannot be insulated to standards. This is also why trusses have increased heels, those are not necessary for structure but they are for insulation.

            Also to say a large builder cannot get something because you cannot does not make sense. They are generally not shopping at Lowe’s. Perhaps you have an insulation supplier in the area that can help.

            Lastly, why would two batts of 5.5” insulation compress more than 11” of the same insulation in a single batt?

          3. Expert Member
            BILL WICHERS | | #22

            Ryan, I don't think "building science" has failed you. All the principles would apply, more insulation, etc., would lose less energy. What has failed you is the building code, and unthinking enforcement of that code. I doubt there is a single professional on this forum that couldn't give you countless examples of inspectors causing problems due to not understanding codes, or applying them incorrectly, or code just being, well, nonsensical. I myself have a story of having a permit rejected because my bold line wasn't bold enough, and I showed the storm sewer line using the wrong shade of green (true story). After a few rounds with that particular city's engineering department, I got tired of the BS and had our lawyers deal with them. The permit was issued rather quickly after that...

            I do agree with you that the requirements to bring old stuff up to code don't always make sense. A 100 sqft addition to a 3,000 sqft house really would make more sense to be held to a standard more similar to the original structure than to current code, due to the small size of the addition. I wouldn't skimp on improved SAFETY codes (i.e. structural stuff), but letting you insulate the ceiling to the same level as the rest of the house would make sense.

            A lot of energy code is reaching for smaller and smaller efficiency improvements. That can be a problem. As a rough example just to show some numbers, imagine a phase 2 energy saving gizmo saves 80% of the originally consumed energy using the old phase 1 gizmo. Now let's say the phase 3 gizmo saves 50% of the energy compared to phase 2. That sounds great! 50% savings! But in reality, compared to what we started with, it's saving 50% of the 20% losses of the phase 2 gizmo, so it's only saving 10% over the phase 1 gizmo. Was the extra cost to go to phase 3 worth it for only a 10% reduction in energy? Maybe not, depending on the cost of the phase 3 gizmo upgrade. When you include purchase price AND installation cost/materials, the numbers often look even worse.

            Now assume you have a phase 4 gizmo that saves another 50% over phase 3. Sounds great! But it's saving 50% of the 10% losses of the phase 3 gizmo, so it's really only a 5% improvement from where we started. This continues on, which each successive generation saving less and less energy in absolute terms, and as you get into smaller and smaller % savings, the cost per unit % typicall goes up drastically. At some point, the cost of the energy saving gizmo will NEVER save any money, which is the economy's way of telling you you just wasted resources over keeping the earlier generation gizmo in place. This is often forgetten when looking at energy efficiency upgrades. You're seeing something similar being forced on you by the building dept people, which isn't really helping anyone.


        2. Expert Member
          DCcontrarian | | #13

          What's wrong with layering batts of insulation?

          1. Ryan_SLC | | #14

            Squish factor plus venting to get R49 in a cathedral ceiling, you're looking at massive rafters or massive furring when structurally I'm more than good at 2x8.

            R49 non high density is 13" something then 1" inch vent (minimum). What small cathedral roof is done in 2x16?

            Additionally, furring at 1" okay. Furring at 2xs the needed structural strength? eek.

            The framing GC doesn't care about that and I am just a homeowner learning this all. I am left with a disappointing effort.

          2. Tim_O | | #15

            I mean, this is the same reason people do double stud walls. Achieving high R values just takes space. For rafters, I've seen gussets with 2x4s. You don't have to use low quality furring strips. Same reason people build double stud non-load bearing walls with 2x4s instead of 2x3s. Quality of the wood makes a big difference.

          3. Expert Member
            DCcontrarian | | #20

            Insulation is thick. No way around that. Not an insurmountable obstacle if it's designed in.

          4. Expert Member
            MALCOLM TAYLOR | | #23


            "Insulation is thick. No way around that. Not an insurmountable obstacle if it's designed in."

            Exactly. I'm working on a small ADU with several shed roofs. One has ended up having trusses 2'-9" deep - even though the span is only 12 ft. That's for insulation, because it allows the wall supporting it to be kept at 12 ft high (meaning it doesn't need engineering), to maintain head height in an attached porch, and for architectural reasons. Using single drivers for the sizing of cavities or service spaces is often what leads to the problems we see crop in here in the Q&A.

      2. jollygreenshortguy | | #10

        Malcolm, it's not for me to answer in Ryan's place, nor am I an expert on the subject, but it's my understanding that burning wood, even in quite efficient wood stoves, results in large atmospheric carbon contributions relative to other heating alternatives that do not depend on combustion.

        There are also many health consequences to air pollution from wood burning. I suspect even with good quality woodstoves indoor air quality may not be so great.

        Like I said, I'm not an expert and haven't read all the studies. But if anybody reading this comment is or has I'd be interested to read their feedback.

        1. Expert Member
          MALCOLM TAYLOR | | #16


          In general I agree, and wood-stoves should be banned where that makes sense, but an outright interdiction isn't always warranted.

          I live in a rural area where logging is still the largest economic activity. After harvest any residual wood is gathered into slash piles, most of which are burned, so there is no more carbon or particulate emissions from that scrap wood if it is instead used to heat houses. There are situations where blanket policies that make sense in more urban areas penalize rural residents. This seems like one.

          1. jollygreenshortguy | | #19

            Malcolm, I agree that a one size fits all policy is likely not to fit anyone very well.
            Just to be clear, I wasn't offering an opinion in my original reply to you. I was just literally answering the question you asked.
            In a few years I'll be moving and building myself a house. I have the possibility of buying a small wood lot as well. If I do I will likely have a couple of good quality wood burning stoves in my home.

        2. Expert Member
          DCcontrarian | | #17

          Around 1550, glaciers worldwide started advancing again after having steadily retreated since the end of the last ice age. This period, which lasted until about 1850, was known as the "Little Ice Age."

          On theory for the cause of the Little Ice Age is that when Europeans started traveling to the Americas they brought with them diseases which the Native Americans had no immunity to. An estimated 90 million of them died. The thinking goes that 90 million fewer people burning wood for cooking and heating, as well as clearing land for agriculture, reduced air pollution enough to cause global cooling.

          If that's the case I don't want to think about what widespread re-adoption of wood burning would do with today's global population.

          1. Expert Member
            BILL WICHERS | | #21

            That seems pretty far fetched. Most of the explanations of that period I've seen attribute it to volcanic activity and solar activity (or rather a relative lack thereof, in the second case). Note that if you look at long term temperature info from back then, a general cooling trend preceded the little ice age period by around 400 years or so, so the trend began well before any europeans arrived in North America.

            Much more likely would be that extensive wood burning would bring back sooty localized smog, similar to what was seen in industrial areas in the early industrial revolution, where industry burned large amounts of coal with essentially no control over the particulate emissions. Areas around Pittsburgh were famous for that in the late 1800s.


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