Basement ceiling insulation required by code — but what about the basement door and stairwell?
HarrisDwight
| Posted in Building Code Questions on
Seems like a huge thermal hole in the basement ceiling. Code requires R30 in zones 4 plus for unconditioned basements. What about the bottom of the stairs (to 2nd floor) and exposed stairwell walls? People typically just use an interior door to the basement, right?
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Replies
Dwight,
I'll have to do a little more code research to determine whether it's legal to build an unconditioned basement. I was under the impression that, according to the 2012 IRC, a home in Climate Zone 3 or higher that has a basement must have basement wall insulation -- in other words, the basement has to be included within the home's thermal envelope. If you can point to a code provision that allows an unconditioned basement, please enlighten me.
Assuming that you are correct, and that an unconditioned basement is legal, it would still be important to maintain an uninterrupted thermal boundary. That means that the door at the top of the stairs needs to be an exterior door with weatherstripping, and that the walls facing the stairway need to be insulated to the same level as an exterior wall. The trickiest area to insulate is the sloping ceiling above the stairway. Good luck figuring out how to get R-30 insulation in that location.
I'll have to check the IRC when I get to the office, but in 2012 IECC: see R402.2.8 Basement walls
R30 on unconditioned basement ceiling (listed as floor insulation requirement in 402.1.1) unless that doesn't fit, then R19 minimum. When basements are unconditioned, hot water lines must be insulated to R-3 and ducts to R-6.
Connecticut is still 2009 IECC, so water lines aren't required to be insulated at all.
Oh, and thanks for the response Martin. I'll have to see about a decent looking exterior door for inside and how to insulate the slope...
Dwight,
I see that you are right. The 2012 IRC provides two options. Basements can be either conditioned or unconditioned. Here is the relevant section:
"N1102.2.8 (R402.2.8) Basement walls. Walls associated with conditioned basements shall be insulated from the top of the basement wall down to 10 feet (3048 mm) below grade or to the basement floor, whichever is less. Walls associated with unconditioned basements shall meet this requirement unless the floor overhead [the basement ceiling] is insulated in accordance with Sections N1102.1.1 and N1102.2.7."
(The words between the brackets are mine.)