Insulation Requirement at Unfinished Basement

[fj80]

Code in my jurisdiction is IRC 2012. Single family residence with unfinished basement.

Do I have to insulate the full height of the basement walls if the basement is unfinished? Or just a portion of the walls so many feet below grade? Which code and section refers to this issue?

Thanks.

 

[Francis Vineyard]

N1102.2 (R402.2) Specific insulation requirements (Prescriptive).
In addition to the requirements of Section N1102.1, insulation shall meet the specific requirements of Sections N1102.2.1 through N1102.2.12.

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 is insulated in accordance with Sections N1102.1.1 and N1102.2.7.

 

[Francis Vineyard]

May the following information be useful;

Virginia does not require a vapor retarder for exterior walls. It is recommended that a vapor retarder not be used in a wall that is partially or fully below grade.

ATTENTION: if the combustible paper facing is not in substantial contact with the backside of the wall finish i.e. gypsum or equivalent, the vapor retarder must be removed. Hence it cannot be left exposed to the interior. Also (foil) scrim paper is not an approved equivalent to gypsum.

The entire depth of this wall cavity should be insulated. This will insulate behind the studs thus reducing the thermal bridging of the wall. While it has been suggested that airspace should be maintained between the masonry wall and the stud wall insulation in order to keep the wall dry, in actuality this will make matters worse. This vertical airspace can lead to a convective air loop, thereby increasing not only the thermal but also the moisture transfer within the wall. If a full height stud wall is used in addition to the masonry wall, this stud wall is often inset an inch or more, increasing the depth of the cavity to be insulated .

If a stud wall is placed on a partially below-grade masonry wall, the stud wall should be insulated the same way as other above-grade walls in the house. When a vapor retarder is not desired, removal is recommended instead of slashing a faced product's sheathing, because narrow cuts are unlikely to significantly increase vapor transmission.

 

[FLSTF01]

Insulate the basement ceiling with R 19. Table 1102.1.1

 

[Paul Sweet]

I also recommend insulating the ceiling. Insulation against a block foundation provides a great path for termites to travel unseen.

 

[Francis Vineyard]

As a reminder if there are a set of stairs to an unconditioned basement with the ceiling insulated as the building thermal envelope; an energy rated door [ref Table N1101.12.3(2)] to the stairs shall be weatherstripped (air barrier) and the walls adjacent to the door and stair insulated similarly as exterior walls.

Also in reference to this design Virginia deleted Section R501.3; Fire protection of floors.

 

[fj80]

Thank you, all. This is very helpful.