Foundation insulation is insulation applied to a foundation, either on the exterior, interior, or below a slab, reducing heat loss through what’s often one of the least insulated parts of a home’s overall building envelope.
Where the insulation is placed depends heavily on foundation type, whether it’s a basement, crawl space, or slab, and on regional building practices and code requirements.
What Does Foundation Insulation Include?
- Rigid foam board on exterior or interior foundation walls
- Insulation beneath a slab foundation
- Batt or spray foam insulation between floor joists above a vented crawl space
- Insulation at the rim joist connecting foundation to framing above
Why Is Foundation Insulation Important?
An uninsulated foundation can be responsible for a significant share of a home’s overall heat loss, particularly in colder climates where the temperature difference between conditioned space and the surrounding soil or outside air is substantial. Insulating a basement or crawl space also tends to improve comfort noticeably, since an insulated foundation reduces the cold floors and drafts that an uninsulated one commonly produces.
Choosing where exactly to place insulation, at the walls versus at the floor above a crawl space, for example, significantly affects whether that space is treated as conditioned or unconditioned, which has implications for moisture control and mechanical system design as well. Energy codes in many regions now specify minimum insulation requirements for foundations just as they do for above-grade walls, reflecting a growing recognition of how much heat loss occurs through this often-overlooked part of a home. Meeting or exceeding these minimums tends to pay for itself over time through lower heating and cooling costs.
Foundation Insulation vs. Foundation Wall Insulation
Foundation insulation is the general term covering all insulation strategies related to a foundation. Foundation wall insulation specifically refers to insulation applied directly to the foundation walls themselves, as opposed to insulating the floor above an unconditioned space instead.