Straw Bale Stucco Cracks

Hi All,

I inspected my first straw bale home today. The home has a post and beam structural system, and separate straw bale walls. There were many hairline cracks in the stucco, some at window and door corners, and some in the field of the walls. The largest cracks were 1/16" wide. How much cracking is acceptable in stucco? Are the standards different with straw bale construction? The foundation was complete crack free. I am writing up the report this afternoon, so any quick responses would be much appreciated.





I see much larger cracks in a wood framed building (here) and anything 1/16 of an inch or less is even acceptable with the Arizona Registrar of Contractors, the state licensing authority for contractors here.

So if the building was here (or anywhere else) caulk and paint would be recommended by me.

I think Dale hit the nail on the head. I see alot bigger and more cracks in stucco in the KC. Metro and the houses are not even occupied. Paul how old was the house?

Kinda like this one. But it is in Utah. It does not even have sod in the yard yet.

Those cracks need to be fixed. If water gets through into the bales you will get mould development. The cracks are well below the protection of the roof overhang.

I am familiar with stucco construction methods and the need to have a proper water proof layer (tar paper) behind the stucco to protect the structure in the event that normal cracks develop and allow water in. I realize that these cracks would not be cause for concern in a typical stucco home.

I am looking for information specific to straw bale construction. Straw bale homes are particularly sensitive to water intrusion, and I am not sure if there is a different standard applied to straw bale homes with regard to stucco cracks. The home was built in 2000.

Paul…if you Google “straw bale homes” there is a bunch of information regarding how their supposed to be constructed.

It would probably be difficult to determine how that one was built without destructive testing.

Paul, You’ll want to pull off cover plates and get remote moisture meter probes into the straw bales in as many places as possible. Once moisture gets into the straw it can be a bad scene, especially if the moisture has no avenue for escape.

I started researching inspecting straw bale homes after a client with Multiple Chimical Senitivity asked me to inspect one. There’s a lot of info on building them, but very little on inspecting them. Much of what’s written is romantacized.

Lot’s of opportunity for bad things to happen with those homes. Lots of liability in inspecting them. You need to disclaim the straw LOUDLY. Many homes leak eventually and with no other type of construction is it so important to avoid leakage. You need to point out to the client what can happen once mold gets going in that straw. A straw bale home with a flat roof is a bad thing, but achitects like to design them to look like southwestern adobes.

Also, the exteriors can be a problem. They used to use stucco-cement which, if it was allowed to freeze during installation… bad. You have to find an inconspicuous place and scrape away at it to determine the condition. If it’s all powdery… bad.

They now often use more high-tech exterior wall coverings but i’m not sure about them. I’d want to know before I accepted liabilty for the inspection.

Most of what I’ve discovered about how to inspect these homes has come from builders. Most of what’s online and in print paints glossy pictures and totally ignores potential problems. I’d charge a lot of money for the inspection and go through my disclaimers carefully beforehand and make sure the client understands the limitations. Mold can total these homes. At least that’s my take.

Good luck,


Most always straw bale homes have large roof overhangs in order to protect from the elements, and for shading purposes.

In the old days when farmers baled hay or straw they had to ensure the bales were not to wet when they were stacked in the hay loft. Why? Bales when damp and stacked can created heat which leads to fire. Many a barn has been lost due to spontaneous combustion. Don’t think there is enough straw in the walls to create spontaneous combustion but definetly mould.

Every once in a while you see a tractor-trailer sitting alongside the highway with a flatbed full of hay bales in flames. Gotta be for the same reason.


Perhaps the trucker threw his cigarette out the window and it landed on the bails? Then again…

There is an old time farmers saying which goes like this.

***If you have barn swallows, you will never have a barn fire.

***When I asked the farmer what that meant he said he was not quite sure. But I have my own theory. I think it means the barn is well ventilated because barn swallows only nest in areas they can access. A well ventilated hay mow will likely not succumb to spontaneous combustion, providing the bales a not packed tightly and to green.

Not an inspector here, but I’ve heard about these houses. Have no idea why you would want one though. I assume they must be cheaper and be great insulators. But is it worth taking a chance on breathing the hidden mold fumes for many years before you realize there is a problem? Interesting about the fire combustion thing. Sounds like a good one for the TV show Myth Busters to test.

I have never inspected one yet.

I cannot confirm that combustion would take place to ensure that no one takes that as fact.

They know about spontaneous combustion of hay bales in TEXAS!

So if’s wet enough to grow mold, it may be wet enough to reach temperatures where it can burst into flames (or at least fill wall cavities/living space with flamable gas).

I’ve learned quite a bit about these homes.

  • Stucco/cement plasters are bad. They are relatively impermeable to moisture vapor and so they trap any moisture that finds it’s way into the walls. Cracks in this material can also be difficult to repair. Earthen, lime or gypsum (inside only) plasters allow moisture vapor to escape more easily, keep moisture levels low and cracks are relatively easy to repair.
  • No plumbing pipes should run through the bales.
  • Flat roofs are bad news.
  • The lower course of bales should be above the finish floor and should have a cappilary break (like plastic) installed under the lowest course so that bales won’t wick moisture if the floor floods.
  • Good flashing methods are key.
  • Long roof overhangs are good.
  • 12" clearance from grade to bottom of plaster wall at the exterior (splashback).
    If these homes are correctly built, straw will be packed tightly between int. and ext. plaster and very litle oxygen is available for combustion. They are actually highly rated for fire. ASTM 119 testing has been performed.

Since you can’t see a lot of this, before you arrive at the site, try to get access to photos of construction, plans or talk to the builder.