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In this Article: The History of Thatched House Building; thatched houses over 80 years old; straw block – characteristics; selection of straw and straw blocks for building a house; how to build a house from straw – stages of work; thatched house and the necessary tools; plaster for straw walls; build a straw house – take fire prevention measures.
The very idea of building a thatched house is perceived with difficulty, because in the well-known story from childhood about three piglets and a hungry wolf, Nif-nif’s straw house looks completely unreliable. And why would anyone build a house from the waste left after the harvesting harvest – there are time-tested construction materials that allow you to build a solid and durable building. True, classic building materials today are not cheap and have a rather large weight, and the walls formed by them have to be additionally insulated. We propose to research the technology of a thatched house and find out whether it makes sense to create such houses in the temperate climate of Russia.
Straw as a building material – history
Straw has been used as a building material since ancient times – the population of Africa has been building houses from it for thousands of years, thatched roofs and thatched attic insulation were very popular in Europe, Russia and Ukraine back in the 19th century. More than 150 years ago, a new technology for the construction of thatched houses appeared – a wooden frame, a plank roof and walls filled with blocks of compressed straw.
The European settlers, actively exploring the territory of North America, faced a shortage of timber in the plains of Nebraska and were faced with the need to live in turf-covered dugouts. The settlers who founded the town of Sandhills were especially unlucky – the local soil was so scarce that it was impossible to remove sod from them without serious consequences for livestock breeding. Local farmers found another way out and began to build frameless houses from straw pressed into bales, coating the walls with an earthen-lime mortar with chaff mixed in it. The increased need for straw blocks led to the invention of mechanical stationary presses in 1850 and mobile balers for collecting straw, transported across the field by horses in 1872, and a few years later, steam-powered balers..
In 1925, in France, panels were invented, formed by straw stalks laid parallel to each other, tied with wire and covered with cement-clay plaster on top. This wall material never gained popularity in Europe, however, in the period from 1936 to 1949, several houses of straw-cement panels were nevertheless built, but only in Australia – local industrialists tried to save on building materials due to the remoteness of the continent from the rest of the civilized world. and the country practically did not have its own resources. A remarkable fact – several Australian houses, built from plastered thatched panels in the middle of the last century, have been perfectly preserved to this day. By the way, in the late 90s, during the demolition of one such house in the town of Altona, the workers unexpectedly encountered difficulties – they could not manually dismantle the walls, they had to call special equipment.
In the 80s, straw housing became popular again, mainly due to the unique combination of heat-retaining, strength and environmental characteristics of straw blocks. More than 110,000 straw houses have been built in Europe, USA, Australia and China in 30 years. Since the mid-90s, several thatched houses have been built in Russia, Ukraine and Belarus.
Straw block characteristics
By and large, straw is a by-product and low-value agricultural product – it can be fed to livestock only after heat treatment and the introduction of additives that increase nutritional characteristics, the roof has not been closed for a long time, but it is only suitable for mulching the soil. Considering that cereal crops are grown on the territory of Russia almost everywhere, there is no shortage of this building material – the construction of walls for a house with an area of 70 m2 will require straw remaining after a grain harvest from 2-4 hectares. Meanwhile, most of the post-harvest straw is usually burned.
What is a straw block? It is a tightly compressed bale, rectangular in shape and consisting of dried stalks of cereals, from which the grain is completely extracted. The overall dimensions of straw blocks can be different, the following are most suitable for construction: width 500 mm, height 400 mm, length 500–1200 mm. Weight of a half-meter block with a density of 120 kg / m3 is about 22-23 kg.
Flammability of straw.Indeed, dry stems of any plant burn perfectly, however, when pressed, it is rather difficult to set them on fire due to the low air content inside such a block. For example, one by one sheets of paper also burn well, but if you try to set fire to a folded pack of such sheets, you will only be able to char them around the edges – the same thing happens with a compressed straw block, despite the high flammability category G4. Since the wall, assembled from straw bales, is completely covered with clay or clay-cement plaster with a thickness of at least 30 mm, the threat of its fire is much lower than that of the walls of a wooden blockhouse.
Low price and availability of material.Blocks can be formed from wheat straw, rye, flax, rice, and hay. The cost of a straw block is ten times lower than that of a brick.
Low thermal conductivity – 0.050-0.065.Straw conducts heat worse than wood (0.09–0.18) and brick (0.56–0.70). The thermal conductivity of the compressed straw is reduced even more if the blocks are formed only from longitudinally oriented stems in relation to the future wall. The energy consumption of a straw house is about 40 kWh / m2 per year, not particularly increasing even in the low temperatures of the Russian climate.
Reducing construction time and volume of work.The assembly of walls from straw blocks is done quickly, without any masonry mortar, does not require the involvement of specialists and construction equipment. For a thatched house, a lightweight foundation is sufficient, usually columnar.
Finally, it is impossible to dispute the environmental characteristics of straw – a natural material that is not treated with chemicals during the construction process, since there is no particular need for this..
Disadvantages of straw walls – insects and mice can start in them, when the humidity of the straw rises above 18–20%, putrefactive processes begin in it, destroying the straw blocks. It is possible to solve both problems simultaneously by pressing blocks to a density of 250-300 kg / m3 – taking into account the thick layer of plaster, it is extremely difficult for rodents and insects to penetrate into such a dense wall, and with an increase in density, a block of straw will absorb moisture worse. It should be noted that an increase in the density of blocks will lead to an increase in their weight two to three times, which will create some difficulties when building a wall. To fight insects, it is necessary to sprinkle them with slaked lime when laying blocks and use lime when drawing up a plaster mixture.
DIY straw house
House wall rails are made of straw bales formed by a baler and tied with a polypropylene cord – you need to choose them carefully. Strapping made of natural fiber or steel wire, sometimes used to create bales in agriculture, is not suitable for construction purposes – the wire rusts, and natural fibers are fragile and prone to decay. In some agricultural enterprises, straw is collected with round balers, straw rolls, in principle, can be rolled out and squeezed with a baler, but it is better not to do this – the straw will be strongly bent, which will affect its thermophysical characteristics.
What is the best straw? Rye or rice, and winter rye straw is most suitable, because its stem is denser, taller and, in addition, winter rye is harvested earlier than other cereals. To build a house, only dry, seed-free and not cut straw is required – you should not form bales of wet straw, you must first dry it.
How to evaluate the characteristics of a straw block? Dry bale no more than one meter long and no more than 120 kg / m density3 can be lifted by hands – it is not particularly heavy. To check the moisture inside it, you need to stick your fingers inside, then take it out and bring it to your nose – when immersed in the straw, your fingers should not feel moisture, when they are brought to your face, there should be no smell of rot. Take a few straw stalks out of the bale and bend them – brittle stalks mean old and stale straw, it will not work for construction. Qualitatively compressed bales practically do not deform if they are lifted by the strapping, it is difficult to put two fingers under the strapping cord, the blocks have similar dimensions.
Like any other building, a thatched house needs a lightweight, but still a foundation. Its type is determined depending on the characteristics of the soil at the construction site. To ensure thermal insulation of the foundation and reduce energy losses of the building in the future, you will need expanded polystyrene sheets with a thickness of 100 mm – they are laid on the outside of the foundation and buried in the ground below the depth of its freezing.
It is important that the floor level in the house is lower than the position of the first row of straw bales – in the event of water leaks, the walls with straw filling are guaranteed not to get wet.
Next, we decide on the type of construction of the house – you can build a building with and without a frame. In a frameless house, walls made of straw blocks perform a load-bearing function, so it is more convenient to use bales with a density of at least 200 kg / m3. In addition, a frameless thatched house can only be one-story, with walls no more than 8 meters long, and the area of openings for windows and doors should be less than 50% of the area of the wall in which they are made. A house with thatched load-bearing walls needs a lightweight roof structure – a four-pitched roof structure will be optimal, the rafters of which are exposed on a wooden Mauerlat made of two boards laid on top of the wall and interconnected by cross members in one meter increments. Roofing material is laid on the pre-plastered end of the wall before installing the Mauerlat. The overhang of the roof cornice behind the wall is more than 600 mm. The advantage of a frameless straw house is its low cost and ease of construction.
A wooden or metal frame for a two-story or large-area house from straw is created similarly to the frame of panel houses. It is possible to build a double-row frame and stack hay bales between two support posts. It is easier to fill the wall sections between the frame posts with straw blocks than to display frameless walls – we will focus on them, especially since the sequence of operations is largely the same.
During the construction of a frameless or frame house, the dressing between the blocks is carried out with wooden stakes or metal rods (diameter 40-60 mm), driven vertically into bales of straw arranged one under the other, stacked in a checkerboard pattern (without matching seams), the higher the rows of the wall are raised , the longer the stakes are needed. The bales are fastened to each other after the fourth row has been laid. Also, metal rods are embedded in the basement of the building with a step of 1000 mm – their length must be sufficient to pierce the blocks of the first and second row.
In frame construction, bales of straw are tied to the supporting posts using horizontal metal pins, and the pins that fix the blocks in their places can be walled up in the foundation and brought out under the Mauerlat by stringing compressed straw on them and clamping the Mauerlat beam using a threaded connection. Neighboring walls during frameless construction are connected row to row with two 30 mm diameter pins bent in a U-shape. It is necessary to perform such fastening both along the outer and inner line of the walls’ mating – at least two curved pins in each row.
Before starting work on the construction of straw walls, you will need to make two simple devices: a press for crimping and bandaging blocks before cutting; several pointed metal hooks for transporting straw bales. The press consists of a pillar about a meter high, dug into the ground and reliably fixed, on which a wooden beam-lever is movably fixed. At the end of the lever, small grooves are cut out, in which a nylon rope is fixed in the form of a loop. A block of straw to be trimmed is placed under this makeshift press, clamped with a looped leg and pulled with a plastic cord in a new location..
The assembly of the walls with hay blocks is performed from the location of the openings and from the corners to the center of the wall. A fine-mesh polymer net should be placed under the bales of the first row as an additional protection against rodent penetration into the walls, between blocks with a density of less than 200 kg / m3 when forming each tier, kraft paper or cardboard is laid – it will interfere with convective heat transfer inside the wall. In the process of laying rows in a frameless structure, you do not need to drive the blocks into their places with significant effort – the wooden guide-stops, previously set along the edges of the walls, can shift. Align blocks in rows according to the level of twine, stretched between the guides, using a board of sufficient size and a weighty hammer. The walls brought out under the roofing structure should not only be secured with hammered pins, but also tightened with plastic tapes in one meter increments – wrapping a metal pin protruding from the foundation below, tying and pulling around a wooden Mauerlat at the end of the wall. A metal tape for tying walls will not work, since it cuts hands and is rather stiff – it is difficult to pull.
In the openings for doors and windows, vertical and horizontal boards are exposed, forming a box, fixed with temporary wooden crossbars nailed to the boards. The lower and upper boards of the box are brought out of its borders – up to half of the adjacent straw blocks. Upon the construction of the wall, the boards of window and door openings are fixed with pins in bales – pins are driven into vertical boards inside the opening, horizontal boards are attached outside it. Before fastening the opening box, it is necessary to lay a roofing felt or roofing felt under the boards, lay a plastic or metal mesh of reinforcement over it with an extension of 300 mm beyond the edges of the opening and fix it with 35 mm galvanized nails or 35 mm construction brackets using a stapler. Reinforcement will strengthen the straw blocks and prevent the formation of gaps between the wall and the opening box.
If the blocks have a density below 200 kg / m3, then the nails and staples will not hold in them – in this case, the reinforcing mesh is fastened with nylon thread or steel knitting wire pierced through the straw through and through. To sew a straw block with thread, you need a homemade needle – a 10 mm metal rod, flattened and sharpened on one side, bent into an L-shaped handle on the other. A hole is drilled in the flattened end – a thread or wire is threaded through it, like a regular sewing needle.
After assembling the walls, they need to be trimmed in those areas where the blocks protrude especially – for this operation and for cutting the blocks during installation, you will need a chainsaw. Before the next stage – plastering – wire communications are inserted into the wall in a cable channel made of self-extinguishing polyvinyl chloride. Plumbing, heating and sewerage pipes are not placed in a straw wall, as they will cause moisture condensation and rotting.
The final stage of work on the creation of thatched walls is the application of two layers of plaster. Nuance – if blocks with a density of 200 kg / m were used3 and above, then plastering can be done immediately upon the construction of the walls. In the case of less dense blocks, wait two to three weeks for the straw to settle and self-compact. It is impossible to use cement plaster, it will prevent the passage of air saturated with vapors through the wall, in other words, it will prevent the wall from “breathing”. Suitable plaster solutions on a clay-lime and cement-lime base, having an average fat content.
Proportions of clay-lime mortar: clay dough (clay mixed in water) – 1 part; lime dough – 0.4 parts; fine-grained sand – 3-4 parts. Proportions of cement-lime mortar: cement – 1 part; fine-grained sand – 3-4 parts; milk of lime (dough of lime mixed with water to a milk consistency). Sifted cement and sand are mixed dry, then milk of lime is added to the container with the mixture until the mixture of the required consistency is obtained.
To reinforce a straw wall from its outer and inner sides, you will need a metal or plastic mesh, with a cell of no more than 30 mm. The first layer of plaster should be thick – about 25–40 mm, leveling the second layer – 2–3 mm, it should be done with a creamy plaster mortar. After the plaster has dried, the walls can be painted with water-dispersed paints – oil paints will not work, since they will act as a barrier in the air exchange of the walls.
Thatched walls must be plastered – attempts to avoid this by covering the straw bales with drywall, plastic or brick will create optimal conditions for rodents and insects, since there will be enough space between the straw wall and the cladding for their life. In addition, panel and brick cladding of unplastered walls increases their flammability due to the same gaps. And one more thing – you should not use a vapor barrier on straw walls, this will lead to straw rot.
Important! In the process of construction work on the construction of a thatched house, it is imperative to observe the following fire safety rules: during the laying of the walls, until they are completely covered with plaster and the perimeter is completely cleaned of scattered straw, smoking, welding and other types of work with heating to high levels is strictly prohibited on the construction site temperatures, using an open flame and accompanied by sparks. Uncompressed straw is highly flammable, and the slightest spark is enough for it to ignite – you can’t joke with it!
During the construction of a thatched house, the construction site must be equipped with fire extinguishing means – barrels of water, loaded and serviceable fire extinguishers, hooks. If a fire does occur, you need to quickly scatter the walls with hooks and fill the smoldering blocks with water – it is important to prevent the wooden frame from igniting (in the case of a frame straw house), since new straw blocks will cost much less than a new frame.
Straw housing undoubtedly has great prospects – in conjunction with eco-house technologies, cheap, using a minimum amount of thermal energy in the cold season and independently air-conditioning straw houses can give their owners more than just environmentally friendly housing.
Is building a house out of straw considered eccentricity or is it actually a breakthrough know-how in sustainable architecture?