R-22 Icynene vs. R-38 Cellulose retrofit

[cdservices]

Am insulating the attic of an uninsulated 100 year old house.

The attic is finished nicely, but has no access above it's flat ceiling. There
is no venting at ridge or gables. Several of the eave storage areas are open,
and I will knock holes for insulation in those that aren't. No access panels
to attic crawl space exist, and I will knock holes there too.

Met with established insulation co. Recommended R-22 Icynene behind kneewalls
and R-38 cellulose on flat ceilings (R-30 cellulose in sloped cavities).

For $1000 more they offered R-22 on pitched roof decks. Not pulling a permit, so
don't need to meet code. They say R-22 is biggest bang for buck, plus we've
got 6 inch rafters.

Question: does extra air seal of R-22 on roof deck outweigh the higher R-value of
the flat ceiling insulation?

[calvert]

CD, The fact that this is a hundred year old house leads me to want some additional information. Do you have any info. on the background humidity levels in the home? Is the basement wet, does it have a dirt floor,... basic dampness profile kind of information? Also what is the roof sheathing or sheathing types, visible from inside as well as to what may have been added to the top side?

Also a little confused regarding your statement that they would install R-30 in closed slope cavities but R-22 in 6" rafters. Are the rafters in the living space of the attic furred to get to a larger dimension to accomodate the R-30 cellulose?

[Bluewoodrock]

Not pulling a permit, so don't need to meet code. .

Question: does extra air seal of R-22 on roof deck outweigh the higher R-value of
the flat ceiling insulation?

#1- The great state of MA requires permits for insulation these days. Not telling you what to do but I've had to pull permits for retro-fit insulation in MA a number of times.

#2- R value is R value, and any insulation that's done should have air sealing done in conjunction. I'd go for higher R value if possible.

[cdservices]

Still stumped.

1. I was taught that air sealing was more important than R value once you got to a certain
level of R value. (R 22?)

2. Calvert. Some good questions. Not sure if the sloping roof is furred, was relying on sub's quote. Basement is dry and has concrete. Roof is sheathed with original boards and 10 year old tar paper with asphalt shingles over.

[Ted S.]

#1- The great state of MA requires permits for insulation these days. Not telling you what to do but I've had to pull permits for retro-fit insulation in MA a number of times.

...and the kicker is...you have to be a Licensed Insulation Contractor or Unrestricted Construction Supervisor.

[cdservices]

Great state of MA makes sure that no good deed goes unpunished. HO wants to better their existing home, and have to pay the state for the privilege. Now, if the reasoning was that the town was scared the careless GC would forget the ignition barrier, I see a legitimate public safety concern. But we all know that's not the reason.

Getting back to the post, I read that R-12 stops 93% of all conductive heat loss. Hence, R-22 Icynene would do a bit better, PLUS stop the air loss that R-38 cellulose doesn't.

[Martin Holladay]

CD Services,
This is an old debate. Spray foam contractors have been spreading falsehoods about R-values for many years, and have (unfortunately) urged people to install lower R-values than the minimum values required by code.

Here's an article on the topic:
http://www.greenbuildingadvisor.com/...n-icynene-says

[cdservices]

Thank you Martin.

From a building science perspective, how would R-22 Icynene for air sealing PLUS R-19 unfaced batts on ceiling perform?

[Martin Holladay]

C.D.,
Where are you putting these products? On a sloped ceiling or a flat ceiling?

Are both products sharing the same rafter bays (or joist bays)? Or do you want to install half the insulation in the rafter bays, and half the insulation somewhere else?

[cdservices]

Martin,

R-22 Icynene on pitched roof and batts on rafter ties.

[Martin Holladay]

CDS,
You can't separate the two layers of insulation like that if you have a vented attic. Is this a sealed attic? If the attic is sealed, put all the insulation in your rafter bays.
More information here:
http://www.greenbuildingadvisor.com/...ditioned-attic