Steel exterior siding/rainscreen on strawbale?

I've seen/heard this mentioned as an option. I like the sound of it; plaster is not my favorite, and it seems to me that this would allow the exterior plaster to be... well. Ugly as sin, for one thing, since it would be hidden under the steel

Certainly I would expect it to be more proof against blowing rain than plaster.

I am puzzling over the best way to affix the steel to the wall. Obviously it needs an air gap. Minimizing penetrations through the plaster seems optimal.

If I build one here in earthquake/rainforest country, it will have a structural timber frame to get the roof up first. Perhaps this could be on the outside of the bales, providing easy attachment for a framework to support the steel?


Windows and door seem like they would be... interesting.


Anyone have any experience?

What problems do folks forsee?

If you use post and beam construction for the roof, the bales could be used as infill.
Remember bale walls breath so any outside cladding MUSt allow this to happen.
If you fastened wall girts horizontally across the posts,  and hung the cladding vertically
to the  wall girls it may work.
What you are doing is unusual but I have seen weather boards [ timber ] also used.
Vertical timber cladding may work for you as well.
I will do some research simply because I am facsinated by your question,
From wall bale cladding
Replied by sabale@bigpond.com on topic Wall lining alternatives
Sisalation is not a good option, a membrane for condensation and not breathable, T'yvec or other breathable options are available.
while some of these fabrics are breathable , some are not rodent / insect or damage resistant. choose carefully, and some may be best protected and or isolated from the straw with plywood, fc sheet or timber lining or the like.

cladding the external of a strawbale wall is known as" Rain Screening " not only used in conjunction with strawbale walls but an internet search will gain you an insight.

some form of sealing the bale wall is required, full cover of the straw with render ( as in leave no straw showing ) prior to cladding is one option, if a clay render this may also be highly efficient in moderating moisture content within the wall.
as a minimum I would use ply lining , then a vapor membrane then an air gap and then the cladding.

is it at this point i should let you know many strawbale professionals offer consulting services,
it's starting to look like your designer may require some experienced assistance.

this is what I searched
srtaw bale cladding

We did a post construction strawbale home with the bales as infill and hung a "curtain wall" on it to install cement board siding with vented soffits. The 2x4 framing is done the "flat way" to keep the wall from getting too thick. The bottom 16" of the exterior walls are treated plywood covered with stucco. The bottom bales are stacked on 1.5" of foam insulation with 2x4's on either side of this to make a stable platform on our cement slab. There is plastic between the bales and the base. The plastic is wrapped up around the bottom bale about a foot on each side but left loose at the top so it can breathe, yet keeps moisture from wicking up. The interior is also framed and we have sheetrock or wood walls with a aluminized rigid foam vapor barrier (all seams taped). It has performed extremely well in our Minnesota hot humid summers and very cold winters for nearly 20 years.

Here is something else from this site
Tyres vs Strawbale

To Dillon's question about affixing siding to a plastered straw bale wall assembly.  Yes, the plaster can be ugly--once the siding is on it won't be seen.  Just don't skip this step as the plaster functions as an air and fire barrier.  How to attach the siding depends on the siding's attachment requirements, and whether it's vertical or horizontal.  Planning for siding during the design stage, framing, and bale stack facilitates this. If, for example, siding requires 2' on center attachment you can use wall framing on those centers, or embed sleepers in the wall that support the furring strips for siding.

Horizontal siding is more common--vertical furring strips attach through the plaster to vertical wall framing members (or can be anchored through the wall to the other side), insect screen at the wall top and bottom prevent critters from getting into the space, and the siding goes on.  Keeping the bales and plaster flat makes it more likely that the furring strips and siding will also be flat.  

Vertical siding presents a challenge. The furring strips are horizontal, which blocks both of the rain screen functions of allowing water to drain down and air circulation so the wall can dry out should water get past the siding.  Each horizontal furring strip needs to have holes in it to allow for this.  

As for what to do about windows and doors, thoughtful design and awareness during construction make this a relatively simple matter handled by flashing and trim details. Doors and windows need to be mounted differently relative to the bale walls when siding will be the finished surface because instead of accounting for just 1" or 1.5" of exterior plaster, there's the plaster plus the space for an air gap and furring strips plus the siding thickness.

My question is about insulating an industrial style steel barn on the inside with straw bales.  8000 feet elevation mostly arid, but with a warmer interior,and a real winter, it seems the moisture would condense on the steel, next to the straw.  

I can think of a couple other options, one is leave a space between the existing steel exterior when I stack the bales in...  the other one would be to make a clay slurry and dip loose straw in then pack it in a form.

Any ideas or suggestions?  Thanks!

Hi Thekla,

If the steel sided barn is already up, the questions I have are what kind of foundation will the bales be sitting on? and if lateral wall bracing is already in place, will it be enough to restrain the bales as well?  Even an an 8' tall wall is quite heavy--a typical foundation is usually reinforced concrete as wide as the bales, and at least 18" deep.  In many parts of the country tension only metal cross bracing can work on straw bale walls, although that system is generally thought to be inadequate in high seismic areas.  

It may also be that you're not so concerned about this as it's a barn?

At any rate, assuming the bales are elevated off the ground/barn slab on  2x or 4x sills that ire anchored to the slab or foundation, I'd set the sills in from the existing steel siding by an inch, and run 1 x furring strip up the inside of the steel siding to help the bales "stand off" the siding and maintain that air gap.  The gap allows moisture moving through the bales to be released at the gap instead of condensing against the metal siding and dripping back onto the bale.  I'd definatley "butter" the bales with clay slip as a fire retardent.  I don't know if it's possible to plaster them with a thick scratch coat before setting them in place.  I wouldn't leave exposed bales with a 1" gap--the fire department calls that situation a "chimney."  Sparks or flame entering near the bottom of the wall would rapidly climb the looses straw into the rafters and roof.  Be sure to install some kind of insect and rodent screen at the top and bottom of the wall, and as the exterior of the bales can't be plastered to provide an effective air barrier, do a good job on the inside plaster.  

You might want to build some kind of top plate above the walls, and perhaps run a few 2 x posts "paired" with the furring strips that are screwed to the metal siding.  Use baling twine to tie the bales tightly from furring strip to the 2 x 4, essentially "basketing" them togehter but maintaining that 1" air gap on the exterior.

You don't say if the barn ceiling will also be insulated? I hope so--most heat loss is through the ceiling.  Plastered R-20+ walls may not do much otherwise.  

Hope that helps!

Thirty years ago I helped wrap the outside of a building in bales which were then stuccoed over, but not quickly enough to keep the vermin out.

Any time we build something we create habitat.  The longer any building is left unsheathed there are entry points for critters.  To them its a vacuum, and nature abhors a vacuum.  We usually install the windows and doors and soffits within a week of stacking the bales, prep for plaster (screed, bead, paper, lath, mesh) and get a scratch coat on the exterior soon afterwards.  Not only does that afford some protection from fire, it keeps things from entering the building.

Thanks folks!


Jim, is the detailed planning on flashing, doors etc something I would find examples of in your book? Or any other source you might suggest?

My building experience is limited to farm structures and my tinyhouse... and I am no yet satisifed with this aspect of the tinyhouse. Once I started looking for examples in my area I began to realize that these details are often handled very poorly even on simpler conventional structures...


Thekla, if you get anything like the amount of condensation on steel roofing that I do... extra care protecting the top of the bale-walls from moisture may be warranted. Perhaps ceiling insulation will take care of this without further work though?

I wonder if assembling the bales in sections, heavily plastering the outside face, and then moving into place would work? If you happen to have a cement floor some arrangment using a pallet-jack might be possible.mm


As far as vermin go.. I know of a mostly uninsulated cabin, occupied full time, on a farm with a booming rat population. They simply stacked a bunch bales against the north wall and called it good... gee, where are all these rats coming from?

Dillon, There are people who have spent a lot of time learning how to build with prefabricated wall panels. The one who writes about it is Chris Magwood, who heads the Endeavor Building School  in Ontario. Check out what he has to say.

Hi Dillon,

The book has lots of window flashing  detail descriptions and illustrations.  We also address what to do on top of the bale wall--yes, it's best that it's closed off from above. A box beam or layer of plaster over the bales is an effective way to do this in an insulated building like a house.  The book doesn't cover straw bale wraps of existing structures whether barns, mobile homes, or existing permanent dwellings, although many of the details in the book would be applicable, because the walls would still need to be supported by a foundation, protected from weather, infestation, and moisture from inside and above.  Finally, the book is a guide for site-built straw bale construction.  We're very much looking forward to when prefabricated straw bale panels are available throughout the United States and Canada, because there's a high likelihood that it will lower building costs while improving consistency in the wall's thermal performance.  Quite a few other benefits.  A few straw bale panel manufacturers have been operating in Europe for several years now, and there's also an Austrian company that has developed "blown in" straw insulation similar to the blown in cellulose (recycled newspaper) we're all familiar with.  Since we're replacing housing stock at the glacially slow pace of 1% or 2% per year, it'll be a very long time before we have replaced or current energy in-efficient housing stock with super energy efficient (and carbon storing) structures.  If the climate change reports are accurate, we have a few decades before we pass the point of no return, and if we believe that better buildings can be part of the effort to dial back our climate changing impacts we also need to upgrade existing housing with air sealing, insulation upgrades, more efficient HVAC systems, etc.  Blown-in straw insulation holds promise there, as do straw or wood fiber insulation panels, because they have a much lower embodied energy and store carbon, unlike most other conventional insulations.