Attic insulation

[Rick Cantrell]

House I was in today, under construction, the upstairs rooms are built into the attic ( attic space above and on the other side of at least one wall).
Questions are:
What is the insulation requirement for the wall?
Also the same wall has a pressed wood hollow core door going into the attic, should this be an insulated door instead of hollow?

Thanks

PS; My IRC is at the office, I'm not.

[Jerry Peck]

Questions are:
What is the insulation requirement for the wall?

Same as for the attic ceiling.


Also the same wall has a pressed wood hollow core door going into the attic, should this be an insulated door instead of hollow?

In *MY* opinion, "Yes.", but we went through a biggie discussion on this recently and I think it was split half and half for the insulated door.

[Rick Cantrell]

Thanks JP,
I thought it should be the same requirement as the ceiling insulation, and I don't think to much of the hollow cord doors either.

[brian schmitt]

walls do not require same r value as ceiling.the requirements are usually found in the energy calcs or prescriptive code requirements for your area. here we require r-38 for ceilings and r-21 for walls to meet a prescriptive approach. skylight shafts extending thru attics get wrapped with wall r-value insulation. i suppose it could differ for your area so ask for the approved plans or ask the inspector what is required

[Jerry Peck]

walls do not require same r value as ceiling.

Quite incorrect when relating that answer to the question posted:

(what was stated)
the upstairs rooms are built into the attic ( attic space above and on the other side of at least one wall)

(the question)
Questions are:
What is the insulation requirement for the wall?

For walls WHICH HAVE ATTIC on the other side, the walls are required to be insulated to the same as the *ceiling to the attic*.

If R-30 is required for the attic/ceiling, then R-30 is also required for the attic/walls.

[Jim Luttrall]

Jerry, do you have a code reference on that?
Jim

[Jerry Peck]

Yes.

(from the Florida Building Code)

The same logic applies to thermal envelopes around the world, though.

13-604.1.A.1 Walls considered ceiling area.
Wall areas that separate conditioned living space from unconditioned attic space (such as attic knee walls, walls on cathedral ceilings, skylight chimney shafts, gambrel roofs, etc.) shall be considered ceiling area. Such areas shall be included in calculations of ceiling area and shall have a minimum insulation value of R-19.

[Jim Luttrall]

I agree that logic dictates that walls in an attic have the same thermal load as a ceiling and the standard R-11 wall is wrong, logically. I was hoping there was something that I had missed in the energy code or IRC that might address it. It is mighty tough to get a vertical wall up to R-38 or R-49 though. I have added more for knee walls on personal homes, but then I did lots of things above code.
Jim

[brian schmitt]

jerry,
a wall has different heat lost due to it being 60 degrees or greater from a horizontal plane(definition per u.b.c.). the greater r-value for ceilings are due to heat rising to a horizontal plane. a wall does not require the same r-value here as you mentioned in florida code. it seems like an exception to the norm but i get the feeling that you can be that also:D . i have little exposure to oher parts of the country and their energy code requirements pertaining to this issue but it would be interesting to know the why and wheres.

[Jerry Peck]

but it would be interesting to know the why and wheres.

From what I read and was told years ago, it's because:

1) 'exterior' walls are applicable as you described, albeit to the outdoor temperature

2) 'attic ceilings' are applicable as you described, *and*, the attic ceiling is exposed to the much higher temperatures of the attic, not 'the outdoor' temperature

3) 'attic walls treated as ceiling area' a combination of 1) and 2), being, as you described, 'not a horizontal plane' but also being exposed to 'the higher temperatures of the attic', thus requiring additional insulation over and above the requirements of the 'exterior' walls

Now, do the 'attic walls treated as ceiling area' require the full insulation of the 'attic ceiling' to attain the same thermal envelope effectiveness as the 'attic ceiling', beats the heck out of me ... but I can tell you that 'attic walls treated as ceiling area' absolutely do require more insulation than 'exterior' walls to attain the same thermal envelope provided by the 'attic ceiling' insulation and that provided by the 'exterior' wall insulation.

Would some 'in between' R value provide the same effective thermal envelope? Maybe, but 'eyes ain't smart 'nough to figger dat out'. :D

[Jim Luttrall]

Here is an interesting document that I came across.

http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/93/930104.html (http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/93/930104.html)

It talks about the loss of effective R value in cold temperatures.

[Jerry Peck]

Jim,

Interesting information, I noticed that was from 15 years ago - wonder what changes were made to loose fill and when?