Timber framed Strawbale wall on ICF stem wall

Hi everyone,

We are building a timber framed straw bale wall which rests on a concrete grade beam (earthern/limecrete floor within) and a 12" faswall stem wall foundation.
The total wall thickness is 2' (6x8 timber post +18.5" strawbale wall),

I've currently placed the stem wall flush with the inside edge of the timber post, seeing that its the timber frame structure that is load bearing, and the bale wall is not. however i am concerned that the "cantilever" of part of the bale wall might seem "unsupported" especially in the eyes of building permit.

Do you see any issue with this, or a better way it can be done?


(Fyi, details of rebar and post to concrete connection not yet drawn)

If the bales are stacked 8 to 10 feet high,

You are looking at 250 pounds per square foot load on that unsupported footing.

IF you can guarantee that the soil compaction will hold the weight of the bales, on the extended footer, cool.

May need a soils engineer stamp.


OR   They make a brick ledge form for the stem wall.
If you use the brick ledge as the top row of forms, then it should hold the weight.

Two things;
- that overhang cannot exist, it needs to be sitting on solid undisturbed ground, not fill.
- Why not include the timber columns within the strawbales?

If that beam had ben centrally located with less overhang, 3 inches it would be ok.

There are ICF forms up to at least 20” wide, and possibly 24”(?)

I see another issue if you are in a hard freeze location.  If you get frost in the “cantilever space”, for lack of a better term, it could exert significant upward force, which might damage the structural bond between your wall elements and the footer.

I’ve seen an old house with a stone foundation with a smooth(ish) wall on the inside, but a very uneven surface on the outside.  The wall was eventually ruined by frost getting between the stone projections below grade, and forcing them apart, like little hydraulic jacks.  I would plan for a sheet foam skirt angled away from the wall to help move moisture away, and prevent some of the frost penetration.

I could be wrong here, but I would check into that.

What  does this acronym mean please?

There are ICF forms up to at least.....

What is ICF   (Insulated Concrete Forms)

Daphne,

I am preparing for my fourth and final concrete pour for my self built single story faswall home. I used about 1300 faswall blocks. Message me if you need any faswall specific advice!

It’s a great product.

You don't say where you're building Daphne (or I missed that detail), but in addition to the considerable wall weight you also need to account for the lateral forces (wind, earthquakes) the wall needs to resist.   You design appears to rely on the interior wall plane to handle both roof loads and whatever lateral forces apply, but not all timber framed joints are up to the task, depending on what those forces are.   I have built 18" and 22" wide straw bale walls supported by floor joists that rest on an 8" ICF stem wall (and suitably wide footing) located to the exterior of the wall where both roof loads and lateral forces are designed to land.   When I have worked on timber framed designs with posts on the interior of the straw bale wall, the posts have been supported by a smaller pier/footing tied into the stem wall supporting the bales.   I recommend you consult an engineer.  Although the Structural Design Considerations Chapter of Straw Bale Building Details: An Illustrated Guide for Design and Construction (California Straw Building Association, New Society Publishers 2019, www.strawbuilding.org) doesn't address your specific question, it offers good background information on calculating straw bale wall weights, and explains gravity loads and lateral forces.

Jim Reiland
Many Hands Builders
S. Oregon