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Community and Q&A

Separating R-value at site/retaining wall

EthanT | Posted in Plans Review on

I’m working on a sloping site and trying to figure out the best way to deal with site wall/earth berming.

The goal is to have driveway/ped access at level 1 but then allow access to rear (upslope) portion of land from second floor.

I’m trying to accomplish this without creating a completely buried wall (for reasons of waterproofing, thermal bridging, fear of ants in foam, etc.), which leads to the shifted floorplans you see in the attached section.

My thought is that the site wall at Level 01 – Grid 1 would be ajust a block/AAC wall and then the interior wall at Level 1 – Grid 2 would be a framed wall with additional insulation (TBD).

Perhaps I am overthinking this and an insulated retaining wall is not a big deal, but it seems hard to insulate, waterproof, etc. compared to a wall that is exposed to the air. Also, this gives me a cool space for storage, wine cellar, root cellar, etc.

So… I was wondering if there is any precedent to creating a site “corridor” as drawn, separating the retaining function from the insulating function, perhaps creating a utility room of sorts

If so, could I essentially add the total R value of these two walls (perhaps the retaining/block wall could be AAC and then the house wall just be a framed insulated wall) with a factor reduction for the convective loop created between the walls?

…basically separating the insulation from the structure…

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Ethan,
    My advice:

    1. Your retaining wall should be built from poured concrete, not concrete blocks (CMUs).

    2. You can choose to put your thermal boundary wherever you want, but you need to know where your thermal boundary is. All of your insulation should follow this thermal boundary. And if any of these walls or floors are made of masonry or concrete, beware of thermal bridges at intersections between the thermal boundary of your house and wall assemblies or floor assemblies that are outside of your thermal boundary.

  2. EthanT | | #2

    Martin

    Thank you for your response... so what I see is that any benefit I may get from moving my thermal boundary in from the earth berm will probably be negated by the complexity of having my thermal barrier (not to mention my air barrier) follow a more complicated pattern... I'm trying to avoid the passive house box... but I see how one gets pushed by practicality towards a 4 corner cube with a cold attic.

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