Window or door bucks are wooden frames that provide the rough opening and structure into which doors or windows will be installed. Conventional houses built of lumber use the same dimensional lumber for these openings as is used in the rest of the wall. Strawbale walls, lacking an integral wood structure, and being up to two feet in thickness, require the additional structure of the buck to provide anchoring for the window or door, and to act as a hard surface against which bales are stacked.
Bucks may be made of 3/4" plywood, and may vary from 12" in width (thus being half the thickness of a 24" wall) up to the entire thickness of the wall. Bucks are often constructed to be less than the thickness of the wall, and the exposed interior and exterior edges of the bales next to the buck are sculpted (often with a chain saw) into a rounded shape that makes the portal more inviting and less intimidating.
Doors and windows should be distanced from wall corners by at least the length of one bale. The necessity of using a running bond stacking method (overlapping the bales) means that at least half of the bales contacting door and window bucks will be less than full size, and will require retying.
Door bucks are installed before the first bales are ever stacked, and are fastened to the slab or foundation using concrete nails or anchors. Door and window bucks are simply boxes which have no sides, and thus are prone to racking (being bent out of square), so bucks must be braced so that they remain vertical and square during bale stacking. Bale stacking begins at the door bucks and wall corners with full sized bales and progresses toward the center of the wall.
When bales have been stacked the full height of the door buck, the buck is re-checked for plumb (vertical-ness), and dowels are driven into the adjacent bales through holes drilled in the buck to securely pin the buck to the bales. Bucks may alternatively or additionally be fastened to the adjacent bales by laying a three foot length of steel mesh on top of each bale course, wrapping about one foot of the mesh up around the end of the bale, and nailing the mesh to the buck. Each mesh layer is captivated by the bale course above, and is additionally pinned by the steel, bamboo, or wood pins used to pin the bales together.
Window bucks are similar to door bucks, with the exception that they usually are not fastened to the slab, but rest instead upon the second or third course of bales. As with door bucks, window bucks are secured by pinning the sides of the buck to the adjacent bales (or securing with steel mesh) after the bales have been stacked.
Experience has shown that window openings represent a very real threat of rain water intrusion into the bale wall, so extra care must be taken to ensure this does not happen. One suggestion is that 6 mil plastic be draped over the top of the bale course upon which the window buck will rest, and extend down the outside of the bale wall to the foundation, and down the inside of the bale wall to the floor. This plastic layer should probably be wider than the window buck by one to two feet to discourage water from spreading sideways along the wall. The plastic layer should be protected, and should not be pierced by any pins or other protrusions.
If the climate is rainy, it would also probably be wise to angle the bottom of the window buck, so that the portion of the buck outside the finished window location slopes down and toward the exterior of the building. This angled bottom plate of the buck will necessitate shims being used under the inner edge of the buck so that the buck rests securely on the flat bale surface.
As mentioned in the Wall Precompression Page, strawbale walls settle, and various precompression methods are used to accelerate this settling. Window and door bucks, being made of wood, will not compress. Empty space must therefore be left above the bucks so that the roof plate can settle with the bales, remain level and flat, and not be held up by the bucks. After the wall has been compressed, insulation (straw or foam) can be inserted into the spaces above the bucks.
Doors and windows represent a significant cost category in total home cost. Some builders may choose to install some windows at a later date for cost reasons. Additional windows and doors (like subsequent room additions) can be planned for by installing window and door bucks as the wall is raised, but filling them with straw (and stuccoing) for the time being. Any future room add-ons should certainly be planned for by including an additional door buck for what will, in the future, become the door or wall passthrough into the new room. Such planning makes later installation of a door quite easy.