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2021 IRC Insulation
- Thread starter Raywesebaum
- Start date
There's actually a lot more history about the attic access than insulation. Notice it begins with "combustible". The requirement for access was all about fire fighter access to the attic in combustible construction. I wrote an article about attics and made a youtube video about this history. A colleague of mine wrote a proposal for the 2024 to remove the reference to "combustible" and it was approved. So, in the future, the evolution of code development will show that the current reasoning is now related to access for insulation and other services and needs for the occupant, and not about fire anymore.
The only thing that stays the same, is that everything will ultimately change.
In this video, I take you through the history of attic access.
I do not understand this comment and am interested to hear more. The attic insulation levels recognize that conventional wood frame construction and 2x12's don't provide sufficient heal height for the required R-values. This is EXACTLY why section N1102.2.1 has always read as as it does. It dangles a carrot of lower minimum r value if you can achieve it over 100%. The goal being getting the shift to high heel trusses over conventional methods of building. But it's always only been a carrot, not a stick.
There are also builders who build the ceiling joists as platform framing and place the rafters on top of the ceiling joists (like a floor) rather than beside them, like a ceiling joist. You do have to contend however with an alternative rafter tie connection since you can no longer use the tables for the nailing, but that's just engineering. It doesn't eliminate conventional lumber.
One of the fundamental concepts of the IRC is to allow for simple and available construction of basic human shelter. For that reason I will fight to my death (as will many others) to ensure there are always methods to build with conventional construction in the model code. I recognize that some urban environments have unique needs due to population density to mandate limited methods of construction, but that needs to be amendments happening outside of the broad application of the model IRC which addresses both urban and rural development.
I have a 1958 house. 22 years ago I had the attic blown. After 20 years of remodels, repairs and additions, the blown insulation was a mess. Last week I smoothed it out and it basically filled the 2x6 ceiling rafters, plus a little. I'd call it R19. Mind you it was such a mess before, with areas piled, that some areas had almost no insulation. My energy bills have not been fun.
I ordered a bunch of R38 batts, a bit too much.
Now I have R19 blown + R38 batt (R57) over everything except the low rafter heels. What's annoying is that fits the framing and insulation materials conventionally, but still doesn't meet the R60 for my climate zone. So that's an annoying number to me. R19 batts in the framing covered by 38 batts sounds sensible, but wouldn't meet code. However, I had extra batts, so I split them and most the center of the attic has an additional R19 staggered over the R38 which is over the R19 blown.
This is a 4:12 pitch over 13 feet, so holy wow, it looks like an absurb amount of insulation (very little space below the rafters). It's laughable.b R76 in the center, R57 at the perimeter, and tapered down to about an R15 or so at the walls. So I'd say it evens out to just a little over minimum code.
So now I'm eager to see in a year, after winter and summer conditions, just how much this insulation saves me in energy costs and how many years it takes to pay back the insulation.
I ordered a bunch of R38 batts, a bit too much.
Now I have R19 blown + R38 batt (R57) over everything except the low rafter heels. What's annoying is that fits the framing and insulation materials conventionally, but still doesn't meet the R60 for my climate zone. So that's an annoying number to me. R19 batts in the framing covered by 38 batts sounds sensible, but wouldn't meet code. However, I had extra batts, so I split them and most the center of the attic has an additional R19 staggered over the R38 which is over the R19 blown.
This is a 4:12 pitch over 13 feet, so holy wow, it looks like an absurb amount of insulation (very little space below the rafters). It's laughable.b R76 in the center, R57 at the perimeter, and tapered down to about an R15 or so at the walls. So I'd say it evens out to just a little over minimum code.
So now I'm eager to see in a year, after winter and summer conditions, just how much this insulation saves me in energy costs and how many years it takes to pay back the insulation.
It all began about firefighter access. Here is my youtube video with my research.
My guess is you won't live long enough to break even.
I'm 45. My energy bills are about $350/mo. The insulation was $1680. You are either expecting me to die soon (WTF bro?) or you expect energy costs to dramatically drop. (I'm cool with that, but not betting on it).
I'm offering you the chance to have a little hope on my dime. Let me pay for your to have a positive thought.
steveray
SAWHORSE
Glenn,
R49 doesn't even fit in a 2x12 (14"), so what do you think they are doing? Nevermind with a seat cut.....Again, you can use conventional framing, but you have to use foam....
Where Section N1102.1.2 requires
R-60 insulation in the ceiling, installing R-49 over 100
percent of the ceiling area requiring insulation shall
satisfy the requirement for R-60 insulation wherever the
full height of uncompressed R-49 insulation extends over
the wall top plate at the eaves.
And now you need 4+" sheathing nails if you are using the insulated sheathing....
R49 doesn't even fit in a 2x12 (14"), so what do you think they are doing? Nevermind with a seat cut.....Again, you can use conventional framing, but you have to use foam....
Where Section N1102.1.2 requires
R-60 insulation in the ceiling, installing R-49 over 100
percent of the ceiling area requiring insulation shall
satisfy the requirement for R-60 insulation wherever the
full height of uncompressed R-49 insulation extends over
the wall top plate at the eaves.
And now you need 4+" sheathing nails if you are using the insulated sheathing....
bill1952
SAWHORSE
steveray - please explain why it can't be over the ceiling joists? (I'm planning on insulating an attached garage that's built with trusses - 22" oc i believe because it's below a two strory roof - and was planning on exceeding the required R49 with blown in cellulose. Top off main house while they are there.)
steveray
SAWHORSE
It won't fit at the eaves.....
mark handler
SAWHORSE
Do the Energy calcs and the Math. There is a point of diminishing returns. Cost vs. Benefits.
bill1952
SAWHORSE
I get that. In my case trusses are 11' aff so I plan to arch ceiling so I can. A rare opportunity. (True for existing though. Good propavents and do best I can, plus around skylight chase and hatch opening. ) Thanks !
Steve, you are missing the entire purpose of the section allowing reduced R-value if able to achieve it over 100% of the assembly. That is specifically because it is known you cannot fit the full depth insulation in the heel cut. It is specifically to NOT prohibit conventional framing and to provide a incentive to use high heel trusses. It's been this way since the first 2000 edition, but was worded much more clearly back then. Its still the exact same concept.
Here's the text from the 2000.
steveray
SAWHORSE
No....im not...
installing R-49 over 100
percent of the ceiling area requiring insulation shall
satisfy the requirement for R-60 insulation wherever the
full height of uncompressed R-49 insulation extends over
the wall top plate at the eaves.
Steve... Please look at the history and then read the 2021 very carefully. The language about "full height of uncompressed" is AFTER you have taken the allowance to reduce from R60 to R49 for using high-heel trusses, not before. It's providing the details for installation that are required for using the reduced R49. and not the R60 taped down at the exterior walls.
Stop and ask yourself what other purpose there would be at all for the reduction, if not what I am explaining?
This is the "choice" it's giving the designers, and has since 2000:
1) R60 with conventional framing, so it's less R-value at the exterior walls, but more in the center.
2) R49 with high heel framing so it's R49 over 100% and not compressed at the rafter heels.
Please take a look at any year edition of the ICC commentary about this section. You know me well enough to know I research the hell out of anything I teach or speak to. Just... take another look at this section.
Stop and ask yourself what other purpose there would be at all for the reduction, if not what I am explaining?
This is the "choice" it's giving the designers, and has since 2000:
1) R60 with conventional framing, so it's less R-value at the exterior walls, but more in the center.
2) R49 with high heel framing so it's R49 over 100% and not compressed at the rafter heels.
Please take a look at any year edition of the ICC commentary about this section. You know me well enough to know I research the hell out of anything I teach or speak to. Just... take another look at this section.
steveray
SAWHORSE
Glenn, what is the seat cut at the exterior face on a 2x12?....Maybe 10"? And then there is 14" R49 insulation and a 1" air space to deal with....I know rescheck takes some of this into account, but this section does not and is clear....
Steve. You keep talking about geometry of seat cut and heel height and I am stopping, reading, thinking, and considering what you are saying. I do not disagree that you cannot get the R49 in the conventional heel height. I have heard you say this and I have responded directly.
I don't feel like you are stopping, reading, thinking and considering the things I have shared and explained. I only say this because it doesn't seem like you are even responding to what I am presenting. Did you look at the text from 2000? thoughts? Did you read any commentary? Thoughts? Did you explain why an allowance for reduction would even exist if not for the reason I have explained. Thoughts?
The IRC gives two prescriptive choices of ceiling R-value. One for conventional framing and one for high heel framing. Why else are there two choices of R-value?
It's all good, my friend. I'm not desperate to convince you of anything, but it's probably starting to look that way.
bill1952
SAWHORSE
If the ceiling drops below top plate, and the bottom of the insulation, would you accept it as full uncompressed coverage and allow reduction? 10' top plate and ceiling at 8' for instance? Intent versus letter of the law....
steveray
SAWHORSE
I get it Glenn....But...it does give 2 paths....install R60 full depth in a "cold corner" condition where it can terminate flush with the inside face of the wall (depth of a plumb cut 2X12 at that point minus ventilation (maybe 11", steeper roof the better))...OR install R49 to the outside plane of the wall (maybe 10")...I don't see how you can argue "intent" when the code section specifically reads:
N1102.2.1 (R402.2.1) Ceilings with attic spaces. Where
Section N1102.1.3 requires R-49 insulation in the ceiling
or attic, installing R-38 insulation over 100 percent of the
ceiling or attic area requiring insulation shall satisfy the
requirement for R-49 insulation wherever the full height
of uncompressed R-38 insulation extends over the wall
top plate at the eaves. Where Section N1102.1.2 requires
R-60 insulation in the ceiling, installing R-49 over 100
percent of the ceiling area requiring insulation shall
satisfy the requirement for R-60 insulation wherever the
full height of uncompressed R-49 insulation extends over
the wall top plate at the eaves. This reduction shall not
apply to the insulation and fenestration criteria in Section
N1102.1.2 and the Total UA alternative in Section
N1102.1.5.
The R49 is the gimmie, but the hitch is that it needs to be installed uncompressed....Don't get me wrong, I am not measure rafter depth, but I know what fits and I give the contractors a heads up on plan review that if they don't have room they will be foaming or finding an alternative path...
Glenn, enjoyed your video on the attic access research.
I pulled out my 1997 UBC and found that it 1505.1 changed from the 1994 code.
Also I looked at my 2003 IBC commentary 1209.2 Attic spaces: Access to the attic provides a convenient and nondestructive means for fire department personnel to visually check for an attic fire and, if need be, gain entry to the concealed spaces and SUPRESS a fire.
So... I beleive that a firefighter with partial ladder in the hole, coat, hat, mask and oxygen bottle can make it thru the 22x30 access. I put the question to my local white hat fireman and was told they don't mess with the access opening anymore, the access hole is never in the same location, preferably in the hallway for thier ladder. I assume that house fires are attacked a little differently now for safety reasons.
Note: Mom's house built in the 50's has a 20x20 access in the garage, I thing firefighters must have been a lot skinner then
I pulled out my 1997 UBC and found that it 1505.1 changed from the 1994 code.
Also I looked at my 2003 IBC commentary 1209.2 Attic spaces: Access to the attic provides a convenient and nondestructive means for fire department personnel to visually check for an attic fire and, if need be, gain entry to the concealed spaces and SUPRESS a fire.
So... I beleive that a firefighter with partial ladder in the hole, coat, hat, mask and oxygen bottle can make it thru the 22x30 access. I put the question to my local white hat fireman and was told they don't mess with the access opening anymore, the access hole is never in the same location, preferably in the hallway for thier ladder. I assume that house fires are attacked a little differently now for safety reasons.
Note: Mom's house built in the 50's has a 20x20 access in the garage, I thing firefighters must have been a lot skinner then
steveray
SAWHORSE
I knew we would get there.....
bill1952
SAWHORSE
I ask again if the full 14" of uncompressed R49 has to be fully above the top plate of the wall OR can some or all of it be below the top plate as long as it extends to the exterior wall sheathing? Something that might look like balloon framing or a dropped ceiling or soffit at the walls both could allow a full uncompressed insulation membrane from wall to wall.