Use light-straw-clay insulation for large light metal buildings?

Are large metal buildings and light-straw-clay the perfect companions?

The latter is a heavy insulation material that requires substantial thickness and weight, about 2x thick and 20x heavy of glass fiber for the same R value.

Can the cost advantages of light metal buildings and light-straw-clay be combined to create affordable energy efficient multistory buildings?

Light metal building example
https://www.texshed.com/50-x-100-x-16-commercial-warehouse-metal-building-v3Vo.html , $80,000 for 5000sqft "shell" is $16/sqft.

Commercially, how much does it cost per cubic ft to make light-straw-clay bulk or panels?

This not clear

The latter is a heavy insulation material that requires substantial thickness and weight, about 2x thick and 20x heavy of glass fiber for the same R value.

What are you saying?

My first concern was  condensation on the inside of the metal sheeting ruining the insulation.
Looking into it ,insulation is a prime remedy for condensation in metal buildings.
I favor clay/ sawdust over clay/ straw, but only because straw seems increasingly difficult to find at a reasonable price.

The LSC would allow vapor to travel to the exterior (in cold weather) and be trapped behind the metal siding, where it could degrade the siding or insulation or both. You would most likely want something to give a bit of venting between siding and insulation. With that, the LSC could probably be used effectively on walls; you would have to do load calculations before using it in the roof. Most steel buildings like this are carefully engineered to support standard loads and no more, unless specifically allowed for.

Hi Douglas,

I think Glenn and William raise really important points.  

Metal cladding presents a vapor impermeable barrier to moisture traveling through the wall assembly from inside to the exterior.  Moisture trapped against the metal would probably begin to decompose the straw portion of the insulation unless some kind of venting, e.g., a vented rainscreen, were part of the design.  

Another issue is dry-time.  The recommendation for 1 week of dry time per 1" of light-straw-clay wall thickness may work well in very dry climates (i.e. the arid American Southwest), but in my experience in temperate S. Oregon it takes much longer for a 12" thick wall (R-21, assuming approximately 10 lbs. per cubic foot LSC) to dry out,.  I have seen LSC walls placed in May go through our hot, dry summers (average daytime temperatures between 90 and 110 degrees, average humidity 30% - 50%) and still be too damp to plaster by October!  If the metal cladding is installed before the LSC goes in, wall can dry in only one direction--towards the interior.  That would likely take much too long and the straw may begin to decompose.  

If the metal cladding plays some role in the building's lateral force resistance design and is installed after the LSC has dried, some temporary bracing needs to be in place to resist wind and seismic forces.

Take a look at IRC Appendix AR Light-Straw Clay (LSC) Construction, a model building code available for adoption in the United States.  The weight, per cubic foot, of a light-straw-clay wall ranges from 10 lbs. to well over 20 lbs. per cubic foot; the different densities have different insulation values.  And that's just the light-straw-clay; doesn't include the weight of sill and top plates, framing, and fasteners.  

There are also requirements for the spacing of framing and reinforcement (against out-of-plane forces).

Since a 10' length of  LSC wall 10' tall with a density of 10 lbs. per cubic foot weighs half a ton (10' x 10' x 10 lbs. = 1,000 lbs.) for the insulation alone, that weight must be taken into account for both the footing design and the building's lateral force resistance (shear wall) design.  This is many times heavier than the much lighter insulations like fiberglass and rock wool that most metal buildings like this, if insulated at all, are structurally designed for.

Are light metal buildings and light-straw-clay insulation a good match?  Maybe.  But the building science and structural engineering requirements for LSC suggests that combining these two systems has a lot of challenges.  

Jim
Many Hands Builders