New and confusing IRC 1102.2.2 R=30 or greater

[Architect1281]

Had a wise designer today tell me that due to design provided space in this code section that they would not need to provide R-38 per zone 5 but could use R-30

N1102.2.2 Ceilings without attic spaces.

Where Section N1102.1 would require insulation levels above R-30 and the design of the roof/ceiling assembly does not allow sufficient

space for the required insulation, the minimum required insulation for such roof/ceiling assemblies shall be R-30.

This reduction of insulation from the requirements of Section 402.1.1shall be limited to 500 square feet (46 m2) of ceiling area. This reduction shall not apply to the U-factor

alternative approach in Section N1102.1.2 and the Total UA alternative in Section N1102.1.3

Designer provided a 2x10 sloped ceiling / cathedral design and said the space was inadequate to put in the 123" R-38 fiberglass batt.

I told them that the space designed was sufficient to incorporate the required R-38 insulation and they just chose the WRONG INSULATION material.

Install 2# closed cell poly expanding foam which in that space and it would be near R-50 so put in enough to attain R-38; says I

Agree or disagree? but the space seem to be of sufficient space to comply? No Es Verdad?

COMPLIANCE IS THE ALTERNATIVE............

 

[mtlogcabin]

Agree. They chose the wron type of insulation to use

 

[Architect1281]

Thanks Mt and I was accused of being petty and mean... which every once in a while is a good thing.

 

[globe trekker]

"1281",

They may not want to spend all that extra money on that faintcy

spray foam insulation.

.

 

[conarb]

Watch out 1281, they'll claim to be environmentalists and that's a religion, environmentalists are screaming at our city council meetings to ban all styrofoam, it's filling the oceans and destroying the planet. Ever seen them install that stuff, it expands and they cut it off throwing half of it into the oceans. Several cities have banned it here and they are trying to get a statewide ban. Firemen hate it too, when it burns it poisons anyone breathing the fumes, so a 20 minute layer of sheetrock or intumescent paint may not protect our heros rushing in to save lives.

 

[pwood]

conarb ,

it is good to see your concern for your dependents. Stanford had a bad night!

 

[fatboy]

Back to the OP, MT nailed it. JMHO

 

[Durant]

Agree with Conarb,

Styrofoam and most of that "Green" products like Great Stuff sealants is pure poision when it is burning. If we are serious about saving energy (and Conarb won't like this) change room sizes from minimum to maximum; example bedroom size instead of minimum of 70 Sq ft; maximum of 120 sq ft.. There is no serious consern for saving energy; it's the manufacturer's pushing products that poison and kill under a cloak of "Green building".

 

[DRP]

IF the area is less than 500 square feet THEN the insulation level can be reduced to R30. Burning foam can be toxic but I suspect the contents would really be the culprit in that scenario.

 

[Francis Vineyard]

Should R.I. later adopt the 2012 requiring R-49 and not delete the same language for R-30 in cathedral ceilings that IMO was explicitly allowed in the 2006 edition then it might be worthwhile to ask for an interpretation from the state. http://sos.ri.gov/documents/archives/regdocs/released/pdf/de89d843829457466a3bca44c73cfa65/4709.pdf

Petitio principii

Francis

 

[GBrackins]

if they can get uncompressed insulation over the outside wall doesn't the code allow the use of R-30 where R-38 is normally required? I'm looking at section 402.2.1 of the 2009 IECC.

 

[Daddy-0-]

Yes. This installation requires raised heel trusses or large rafters to allow for uncompressed insulation over the top plate. A little tricky to frame and requires advanced planning.

 

[Architect1281]

to Francis Vineyard? trouble with that for them who asks the statr is I'm the guy they ask...and we are already on the IECC IRC 09 workin on the 12

which give the space provided would even meet the R49 that that will require.

Daddy O the space provided can hold 9.25 " of spray poly 2# at 5.5/ in can attain 50.5 R value so I told them the space designed is sufficient to attain the required R 38 so comply.

GBrakins different situation but that one we do at heel - this situation is 2x 10 cathedral rafter - no attic space.

 

[Architect1281]

COnarb and Durant oh yes when they are done removing the overexpansion it fills the truck

not my material of choice as a designer but as a CBO don't tell me you can't comply by picing a less r/inch product by choice

when compliant material is available.

 

[Sifu]

It has been my understanding that if the r-30 can be installed uncompressed it can be permitted for up to 500sf per house. They would need to use r30-c which is 8 1/4", so when adding the 1" air-space they won't exceed the 9 1/4" cavity. I permit this installation routinely. The use of RESCHECK would almost always allow this installation as long as the rest of the project meets prescriptive values. A few neighboring AHJ's have adopted 2012 but specifically amended the use of the prescriptive tables to continue using the 06 R-value tables.

 

[Francis Vineyard]

COnarb and Durant oh yes when they are done removing the overexpansion it fills the truck not my material of choice as a designer but as a CBO don't tell me you can't comply by picing a less r/inch product by choice

when compliant material is available.

R101.3 Intent. The purpose of this code is to establish minimum requirements to safeguard the public safety, health and general welfare through affordability, structural strength, means of egress facilities, stability, sanitation, light and ventilation, energy conservation and safety to life and property from fire and other hazards attributed to the built environment and to provide safety to fire fighters and emergency responders during emergency operations.

How do you define affordable? It's not expensive if you make more money you can afford it! FWIW Virginia amended this to say "at the least cost".

N1102.2.2 Ceilings without attic spaces. Where :Next('./icod_irc_2009_11_par014.htm')'>Section N1102.1 would require insulation levels above R-30 and the design of the roof/ceiling assembly does not allow sufficient space for the required insulation, the minimum required insulation for such roof/ceiling assemblies shall be R-30. This reduction of insulation from the requirements of :Next('./icod_irc_2009_11_par014.htm')'>Section N1102.1 shall be limited to 500 square feet (46 m2) of ceiling area. This reduction shall not apply to the U-factor alternative approach in :Next('./icod_irc_2009_11_par016.htm')'>Section N1102.1.2 and the Total UA alternative in :Next('./icod_irc_2009_11_par017.htm')'>Section N1102.1.3.



My understanding of the new language is allowing an exception of up to 20% or 500 sf of area prescriptively. Using the logic that foam insulation can be used to comply would also contradict with reduce R-value exception in the previous section for the rafter heel area above the top plate. Probably should amend the rafter with ceiling span tables "size/span permitted with foam insulation only".

REScheck now includes rafters without attic space but I'm not familiar with how the software calculates in this area, can someone advised?

Francis

 

[STB]

Rescheck has always had some form of "rafters without attic spaces" I believe it was labeled Cathedral Ceiling. You have to input the square footage of the sloped area (measured on the angle). The flat ceiling sections are entered seperately. The problem is if they choose to use Rescheck, it should be used for the entire building. You cannot mix and match between the prescriptive code requirements and a calculated approach. Hope this helps.

 

[Francis Vineyard]

STB Thanks for you repl. REScheck has been updated with a new drop down menu and instructions explain there is little difference than the ceiling with attic; but I found my answer experimenting with different inputs. It does not allow the exception but it does assume rafter size based on batt insulation with 1 inch space for air.

Francis