Updated: Feb 9, 2021
A well-built wall should be strong and tightly insulated to seal all joints solid. If we look at masonry walls - they should be straight, with staggered brick and just enough mortar to seal any openings between individual bricks. Let's imagine the builder let some small holes in between (imagine looking inside out and see light patches of the sky) - not to worry still - that is sealed by plastering the walls from both sides. Both inside and outside must be plastered before insulating from the outside to ensure air-tightness (sticking polystyrene sheets on the wall does not eliminate air movement).
So to get a quality masonry wall there are processes and steps which cannot be avoided.
Possibly the most important aspect of a straw wall is its ability to work exceptionally well with water vapor and moisture. We plaster inside walls with a thick clay plaster which acts as a variable membrane itself (by buffering and conveying humidity in both directions depending on the inside conditions). This way the integral compressed straw within the module serves as a true vapor-permeable core, a thermal insulation plastered with a humidity controlling layer of thermal mass (clay).
The clay plaster does indeed do wonders to control the humidity on the inside - but it does not fare well exposed to the elements outside. If plastering the outside walls then lime plaster can be used instead. It is much harder and resilient to direct moisture and wetting than clay is and can serve as an exterior layer.
In case the project allows it - we would recommend to finish the outside walls with a ventilated facade for optimal results. The outside would be wrapped with vapor permeable membrane, taped to be sealed. An additional natural insulation layer is nailed on top to both protect the membrane physically and help keep it warm in low outside temperatures to push the point of condensation outwards - beyond the membrane. Excess moisture from the exterior insulation is then naturally ventilated in the 50mm gap behind the facade.
When building a straw module wall - there is a sequence to keep in mind and they start to go on quick. Make sure the foundation is straight and level - this will help immensely to layout and form the ring beams. Our cuts are precise and square - take your time to build the ring precisely! A task which is not to be rushed through in order to get the final wall fitted to the millimeter.
A normal-sized straw module can be about 120cm in width and about 240cm high. Such a panel can weigh about 150kg and moving it around to position could greatly benefit from a platform cart or ideally - a crane.
Straw module plan includes a layout of the modules, their dimensions and bracing - it can be produced by your construction engineer with our help, or the assistance of our experts.
Getting yourself familiar with the building and the straw module plan is going to help start the building process straight off the truck - every corner module of the house is typically braced to combat earthquake and high-winds pressure. It is easy to identify them even while they are far away or lifted by a crane and it is impossible to read the label - positioning them where they are needed is half the work of getting them installed.
Consider starting the wall assembly from a suitable corner of the building to establish a perfectly matched, braced module to lead the installation of the rest of the walls. Adding more panels to the established corner is just a matter of pulling them tightly to the prior one and fixing them in place with screws.
Once the wall is assembled and the modules are fixed in place - the exterior membrane must be wrapped and taped to the hydro insulation protecting the wooden ring from moisture coming up from the concrete. Remember that a wooden board must never touch concrete without proper insulation!
With straw walls fixed in place and wrapped, you can relax - the wall can withstand the bad weather until the next suitable moment - and complete the roof as well.
So - we know what’s important and what to be careful about when assembling the wall- let’s try to make out the steps:
A foundation, done right - the closer to flat and level - the easier it would be for the next step;
Double ring beams must be constructed to layout the walls - perfect leveling and secure attachment are key! The ring is anchoring the whole wall down and must be fixed with care. Make sure to insulate the foundation and leave some extra material to overlap it with the exterior membrane (if applicable). Precise placement would facilitate further wall assembly;
Start with braced modules to form the corner of the building - having a level ring to attach to would be essential and help tune the first two to a perfect vertical.
Line them up one by one - fix with screws to the previous one and bottom ring and proceed onward.
When modules can only be fixed in a single side/plain, like modules serving as headers (or lintels) above windows or door-frame - they must be solidly supported from below (with plywood capping the side of panels or doubled timber in that area). This way we can cover about 3 meters of header span and thus allow for spacious window views.
Having walls connecting all the corners means that it is time to “wrap-up”! The membrane should be overlapped and “taped” to form a perfect seal - but leave some extra on the top to seal with the inside vapor control membrane coming from the roof.
The straw wall can now be tied together with the top ring, a mirror of the lower one - to lock the individual modules into a solid wall.
Roof construction is not something we would be going into, due to the vast differences and flavors that are possible.
Building a straw house requires attention to detail where it matters most - installing accurate ring beams and ensuring outstanding moisture permeability of the finished wall by combination of inside plastering and outside membrane wrapping.
A straw house can last for a lifetime (and even more!) if it is built well and cared for.