Protecting Your Straw Bale Home from Weather –

Written by Andrew Morrison

drop of water fallingA justifiable concern is protecting your straw bale home from weather. Water damage is the worst enemy of bale construction and as such, is protected against with the up most attention. There are several ways to deal with water issues in a straw bale home. Rain splash, direct rain contact, humidity, leaky wall openings, and water line breaks are all potential sources of water damage. Each can be handled, to an extent, with proper planning and construction.

Let’s start with the obvious: rain. This is perhaps the easiest form of water to deal with in a straw bale home. Large overhangs, preferably 2′ or more, will direct the majority of the rain away from the walls by protecting them from direct contact. With the application of gutters on the eaves, you can virtually eliminate rain from contacting the walls. The gutters also give you the opportunity to collect your rain water for future use. If you have a multiple story building, be sure to add roof lines at each story. Intermediate roof lines serve the same purpose of directing rain away from the walls. Without them, the roof on the second story will not provide enough protection for the first story. Areas with high wind driven rain or horizontal rain, are a different situation and are harder to build straw bale homes in.
water isolation walls

Pipe leaks are another common place of water damage in straw bale homes. These are also easy to deal with. KEEP ALL PLUMBING OUT OF THE BALE WALLS. Sorry to yell, but that needs to heard. I keep all of my plumbing to interior walls where possible. If that is not possible, I build what I call water isolation walls, like in the example above.

By stopping the bales before we encounter plumbing, we are able to isolate it entirely from the bale walls. The area where plumbing has to be on an outside wall, like a kitchen sink, can then be insulated with extra insulation and the wall framed out to meet the same plane as the face of the bales. This eliminates any risk of the water leaking directly into the bales. The 3 1/2″ toe ups also eliminate the risk of the bales soaking up the water off of the floor from a broken water line.
Andrew Morrison window corner detail
Although I look a little crazy in this shot, I am just fine. (Thanks for your concern though) I am pointing out the tiny corner detail in the first piece of counter flashing. Notice that the piece that is cut is not cut all the way to the corner. It has a little extra flap that is folded into the window on top of the sill. This piece, when covered by the next level of counterflashing, creates a total seal in the corner. A small bead of silicone caulk can be a friend here as well. Check out the next shot:
window flashing on straw bale wall
The sill and legs of the window frame have been completely counterflashed and THEN the window is installed. Once the window is set, then it is time to go back and flash the window in its entirety, including the head which is left out of the counterflashing. This extra step is worth the effort. Windows are notorious for leaks and are certainly a place you want to spend some extra time protecting.
man with sweat on his back
Now the hard one: humidity. The reality is that humidity cannot be stopped. It can be drawn out of the air with dehumidifiers, but it cannot be eliminated. If you live in a high humidity area, straw bale construction is probably not a good idea. If you live in a climate where the humidity gives way to hot and dry days, for an extended period of time, that may be enough for the bales to dry out. The deal is that humidity pervades everything and so cannot be adequately controlled.

If the bales reach a moisture content by volume of over 20% then they will sustain mold growth and will rot. Exactly how the relative humidity rating of the air translates into moisture content by volume per bale is not clearly defined, at least not to me. If you consider your climate tropical, I would say no to straw bale construction. If you are right on the edge and unsure, I suggest you build a small structure first and install moisture meters to monitor the moisture content. After a year or so, you will have sufficient data to make a more informed decision.

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58 Responses

  1. We plan on spraying the strawbale walls using a Tirolessa applicator. Can we spray hydraulic lime plaster? We have built a hybrid strawbale house and only the North and West walls are straw. Appreciate your advice and help.

    Thanks. Rich

  2. I live in the Cincinnati Ohio area and want a scramble home but fiance says no because of humidity, rain, rodents, etc is there someone in this area that he can talk to to ease his fears or is he right about any of it in this area.

  3. We are struggling to protect our bales prior to construction I.e in the paddock. How sensitive are they to weather and wind before you use them for building?

  4. Hi Anna. They can be very sensitive to moisture. It is paramount to protect them from moisture, especially rain and snow, very well before, during, and after construction.

  5. Brandy, we built our strawbale house outside Berea, KY using Andrew’s guidelines. We would be glad to have you down to see our place if you are still thinking about it. mary dot kniskern at gmail dot com

  6. Mary! I live in Cincinnati and would love to check out your project! We are considering a straw bale house for our addition in Montgomery Ohio. I’ll send email. Grant

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