Insulate poured concrete retaining wall inside or outside?
user-2701121
| Posted in Energy, Heating & Insulation on
We are planning a remodel of a portion of our home in San Francisco (climate zone 3). Our foundation will be slab on grade, with stem / retaining walls (forgive my possibly incorrect terminology here) extending 2-4′ up from the slab to hold back the exterior grade (in other words, our rooms will be partly below grade).
I’m wondering about insulating these retaining walls – is it better to put the insulation on the interior side of the concrete walls, thus making them part of the unconditioned part of the building – or is it better to put the insulation on the exterior of the walls, making the walls into thermal mass inside the building?
Replies
From a durability perspective, it would be best to insulate from the exterior. There may be some slight performance benefits to insulating from the exterior as well. Building Science Corp has done a lot of research on this and I'm sure you can find some information on their website: buildingscience.com.
That said, it is often a challenge to detail the insulation outside of the concrete wall. Rigid foam is the most common type of insulation used for this and it needs to be covered and protected, you have to determine how it relates to the wood-framed wall above, etc. Builders often choose to insulate these situations from the inside instead because it often makes the details less complicated.
To give a more helpful answer, we'd need to see your assembly details, a section of the full wall. And keep in mind that water management is going to be critical here, with the rooms sitting below grade. Make sure to have all of your waterproofing and drainage details worked out before the concrete walls are backfilled.