Window and Door Flashing in a Straw Bale House

Written by Andrew Morrison

Andrew Morrison flashing windowPerhaps the most important aspect of straw bale building has nothing to do with bales. In fact, it has everything to do with holes in the walls. Windows and doors present the most likely areas for water infiltration and bale damage in the entire house. For this reason it is extremely important to pay extra attention to these areas during construction. For windows, I use two part process. The first is called counter flashing and is put in place before the window or door is set in the opening.

Starting at the bottom, a waterproof membrane is applied to the opening and then built towards the top so that each layer overlaps the one below it. In other words, the top of the counter flashing for the bottom window sill is underneath the bottom of the side jamb flashing, and the top of the side jamb flashing is underneath the bottom of the head flashing. In this way, any water that contacts the counter flashing will always be moving down and always end up on top of the counter flashing. I use adhesive flashing for this application.

Once the counter flashing is in place, I install the windows. After the windows are all secured, I wrap them in an adhesive flashing again starting at the bottom and working my way up to the top. The top most piece of flashing must always be above and on top of the layers underneath it. The adhesive flashing works well because it completely seals to the windows and framing. Be careful not to get straw behind it during installation as that will create areas for water to find its way into the building.

I always set my windows flush with the outside plane of the wall, not inset like in adobe houses. The look is a bit more basic than the adobe feel, but the risk for water infiltration is considerably lower. This is just another detail that is something to consider when designing a home. How can I best protect my bales and thus ensure a long life for my home. A simple change in design allows for better protection and a better ability to flash against the elements.

For doors, you can lower the base of the threshold into the floor if you are using concrete by creating a void during the pour. It is also possible to use sill pans underneath the threshold to improve the seal or even use a large bead of high quality caulking beneath the door threshold. These products greatly improve the installation of the door and are worth the extra effort. The side jambs of the door are flashed in the same manner as windows, from bottom to top as is the door head.

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6 Responses

  1. Where can I get the flashing you show in this entry? I have not seen the door pans before and they seem like a great idea. Also, do you use metal flashing above windows and doors? If so, how do you install metal flashing over a window like the one in the picture?

  2. Athena,
    You should be able to pick up the adhesive flashing at any quality building supply store. The pans are a little harder to find. You can often find them at door supply stores (stores that specialize in doors and door hardware) or even at the same building supply store as the adhesive flashing. We do apply metal flashing to the heads of our windows if they will be exposed to weather; however, most of our homes are designed to protect the walls from direct contact with rain by the use of large overhangs and secondary roofs. If we do have a curved top window that needs a metal flash, we use copper. It can bend and be nipped off to fit just about any shape. It is expensive, so we only use it when we really need it. The window in the picture you refer to was on a small building with a low profile and large overhangs. We did not use metal on that window.

  3. Hi Andrew,
    this is not strictly a flashing question, but is certainly related.
    I think that when we buy windows (and doors) we specify that they come WITHOUT reveals – since the rendered wall itself is the reveal. The window /door slots in between the posts either side (with lots of suitable flashing of course…) Is that right?
    Regards, Peter

  4. I am not sure I understand your question as best I should. The windows I use have a nailing fin that is “welded” to the window. The window itself sits proud of that fin by 7/8″ which allows me to finish the plaster to the window edge with a slight curve towards the frame for architectural looks. The flashing goes over the nailing fin with an added “head flashing” that extends over the window sash/jamb. This is also called Z flashing because of its shape.

    Doors are a little different. they install flush with the wall and are trimmed out with the plaster finishing to the trim. The flashing is applied over the door jamb and then the trim is installed. A head flashing is once again placed over the top piece of trim to direct water away from the opening.

    I hope this helps.

  5. Hi Andrew,
    yes, it DOES help. Windows here come with a supplied reveal – usually a hardwood frame that can be nailed through to the surrounding posts. This sounds like a bit more than the nailing fin you are talking about. I will try to find a pic to send you. I couldn’t find any diagrams in your book setting this out in detail?
    Regards, Peter

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