Strawbales against an impermeable wall

Hi all,

I know of the need for a strawbale wall to be breathable from both sides. However, I'd like to know in which cases or under which conditions straw bales could be used to internally isolate an impermeable concrete wall. I could start building a strawbale house in the next months following the GREB technique but this house has to be built against the neighbour's wall. As result, three of the walls will be fully breathable but not the wall being shared with my neighbour's house.

I was initially assuming that this shared wall had to be isolated with industrial materials.

My neighbour's house will be (still not built) a 1-storey house so I was also considering to build the concrete (or brick) wall only for the first stage and then make a full second storey with strawbale. However, there is the risk that my neighbour decides to build a second floor in the future, closing the permeability of my second floor's wall as well.

Thanks in advance for your comments.

Daniel.

Hello Daniel......Welcome!

I know of the need for a strawbale wall to be breathable from both sides. However, I'd like to know in which cases or under which conditions straw bales could be used to internally isolate an impermeable concrete wall.

Not something that is ever recommended. SB has to have good (excellent actually) air circulation on two primary sides to function well. Even the SB roofs that have been attempted don't last long unless a "cold vent" space is part of the system.

One could imagine placing the SB so that you have a "venting space" kind of like a "rain screen wall" and this..."may be"...is sufficient enough to allow the SB to be used in a common wall application. I am not sure I would take that risk and just insulate (perhaps?) with something like mineral wool board and/or heaving double layer wood planking, cordwood, or some other "permie" method.

Because of the "common wall" challenges, and not really seeing/understanding a complete model or blueprint concept, it is difficult to give complete guidance of any great value...but perhaps others can share there personal experience of such a condition. I would not recommend (nor do I often) any type of "structural" SB wall systems for first time builders unless the "building team" has either seasoned SB builders/PE support. Structures with an internal framework (usually wood...and I like timber frames.. but that is just my subjective view) are typically much stronger and/or free up some of the design challenges that a structural SB wall may have.

Common walls can really be a challenge down the road also, unless there is a "housing cooperative" or some other "guidelines" of what this wall should consist of. Then there is the very large issue of proper roof drainage!!! Any time a roof's drainage system is directed anywhere near a "common wall" area there is inevitably accumulated moisture challenges, often that go unseen inside the wall area.

Sorry not to be of more help... Some job site picture would really help or perhaps some design plans, if you would care to share them. Folks here love seeing them and it helps to better understand the project.

Daniel, here is a detail of what I would do. That wall is going to be very well insulated and sound proof, around R-35. The only way is to dry to the interior and attic or I'd run that vent through a vaulted ceiling to a ridge vent. You'll want to control the indoor humidity at all times to less than 40% RH to keep the building healthy. Leave a vent gap behind baseboard molding.

Strawbale is a great choice. You do not need any wood. Strawbales outperforms wood in most cases especially seismic. IRC 2015 now has strawbale code which is prescriptive/empirically based on successful builds throughout the world for centuries. Follow it.

See we really did not a drawing nor redesign your home to answer your question.

Good luck!