A house built with straw and plaster costs little and is environmentally friendly. This guide describes the techniques and materials needed to build a durable thatched house with a good energy class and low maintenance costs. To simplify things, the guide does not indicate instructions on installing services such as gas, water drains, electrical systems. We will simply learn how to build the structure.
Steps
Step 1. Make a plan
How big should the house be? With how many rooms? With what services? Where do you want to put the doors and windows?
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Draw the ground floor. Sketch the placement of the rooms and identify the drains (shower, bathtub, toilet) to be placed in the concrete foundation. A raised wooden floor with a cavity below will allow you to change the layout later.
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Each section of the outer wall should be a multiple of the standard length of the straw bales you intend to use. This way you will minimize the number of bales you will have to cut, reducing waste.
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Step 2. Decide what kind of foundation to use
The most common choices are a poured concrete or log base with a double outer perimeter and central beams supported by columns on which the joists and floorboards rest. Check your local building codes for the required technical specifications.
Step 3. Lay the foundation below the surface in colder climates, where frost is expected
The surface must be level, whether you are building in the hills or in the plains. Check building codes for the size and composition of the foundations of the exterior walls. You will then need to add the water pipes, electrical and gas systems over the concrete foundation, then through the wooden floors, walls and ceiling.
Step 4. Build a wooden or metal frame
The frame will transfer the weight of the roof to the foundation, so it must be strong. You can add wooden reinforcements diagonally, from the ground corners to the ceiling, to prevent lateral movement. Each pillar must be anchored to the foundations. You can also pull cables between the straw bales to increase stability and relieve any thrust and displacement of the bales.
Step 5. Keep the construction site sheltered by placing the roof in place before continuing
This way you will avoid exposing the straw bales to rain, snow and ice during construction.
Step 6. Build the walls with straw bales, not hay
Straw is obtained from wheat stalks (never use hay bales). They must remain dry, below 20% humidity, and must be well compressed to prevent moisture from penetrating before being plastered. Both of these factors are important to prevent the bales from rotting after construction. Start making some chopsticks by pointing willow branches with a diameter of about 2.5 cm. You will need to plant them in the foundation, making a hole or making them penetrate the still fresh concrete. The bales will then be reinforced with other U-bent branches. You can bend the willow branches when they are still green, or you can use another type of wood and metal rods for the U's.
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Take a one-meter-long branch and make two marks 33 cm from the ends, then hammer the branch in these places until the wood is frayed. This way you will be able to easily fold it into a U. Each row of bales must be secured to the one below with these U-shaped reinforcements, staggering them from the row below. It is important to place these reinforcements, especially in the upper rows. Once you reach the roof you can add a reinforcement that goes through the entire height to give even more stability to the wall.
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Step 7. Plaster the walls
There are many types of plaster on the market, some are obtained by mixing local ingredients. Choose the best one based on availability, cost and functionality with respect to the climate of the area. Apply the plaster with the appropriate tools to obtain a smooth finish, or with your hands for a more rustic effect. The important thing is to completely cover the straw: no corner must remain uncovered, otherwise a possible fire will spread faster and humidity and parasites will penetrate the walls.
Step 8. Install doors and windows
You should have left openings for doors and windows, supported by lintels. Install the frames, attaching them to the frame or supports in the walls.
Step 9. Apply a breathable paint
Look for a mineral silicate paint without artificial resins, hydrocarbon-based solvents, or insecticides. The paint must be outdoor, UV resistant. These paints apply normally, but follow the instructions on the package as the composition can vary. Before applying the paint, make sure that the walls are solid, clean, dry and well degreased.
The breathable paint allows moisture to escape from the walls. Paints are classified on the basis of a transpiration coefficient, called SD. Paints with a high SD value do not let the wall breathe. Usually on non-breathable paints this value is not even indicated, being sometimes well above 3. Paints suitable for straw houses have an SD value lower than 0, 1
Advice
- A 60 cm thick straw wall has a very high R-value (insulation capacity), around R-33. Since the walls are plastered both inside and out, the insulation is very good.
- Thatched houses are becoming more and more popular. Search the internet for examples in your area.
- There are many useful articles on the net regarding the design and construction of thatched buildings. You can attend a construction course, or watch a video, read the most frequently asked questions, consult various photo galleries.
- Building a straw house is easy and fun, you can even build one to let off steam in the real estate market!
Warnings
- This is not the ultimate guide, they are just tips. Consult other sources as well.
- Be sure to follow local health and safety regulations to avoid getting hurt or hurting your helpers or family.
- Check the availability of materials on site and the necessary permits before starting.
- If the law requires building permits, consult a construction engineer before starting to build. Often the construction of thatched houses is allowed in rural areas, but not in the city.
