Straw as a Building Material

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BASIC:
Straw, grass, and reeds have been used as building materials for centuries. Straw houses have been built on the African plains since the Paleolithic. Straw bales were used in construction 400 years ago in Germany; and straw-thatched roofs have long been used in northern Europe and Asia. In the New World,teepees were insulated in winter with loose straw between the inner lining and outer cover.[6]

Pilgrim Holiness Church in Arthur, Nebraska Straw-bale construction was greatly facilitated by the mechanical hay baler, which was invented in the 1850s and was widespread by the 1890s.[6] It proved particularly useful in the Nebraska Sandhills. Pioneers seeking land under the 1862 Homestead Act and the 1904 Kinkaid Act found a dearth of trees over much of Nebraska. In many parts of the state, the soil was suitable for dugouts and sod houses.[7] However, in the Sandhills, the soil generally made poor construction sod;[8] in the few places where suitable sod could be found, it was more valuable for agriculture than as a building material.[9] The first documented use of hay bales in construction in Nebraska was a schoolhouse built in 1896 or 1897. Unfenced and unprotected by stucco or plaster, it was reported in 1902 as having been eaten by cows. To combat this, builders began plastering their bale structures; if cement or lime stucco was unavailable, locally obtained "gumbo mud" was employed.[9] Between 1896 and 1945, an estimated 70 straw-bale buildings, including houses, farm buildings, churches, schools, offices, and grocery stores had been built in the Sandhills.[6] In 1990, nine surviving bale buildings were reported in Arthur and Logan Counties,[10] including the 1928 Pilgrim Holiness Church in the village of Arthur, which is listed in the National Register of Historic Places.[8] Since the 1990s straw-bale construction has been substantially revived, particularly in North America, Europe and Australia.[11] [edit]Method

Straw bale building typically consists of stacking rows of bales (often in runningbond) on a raised footing or foundation, with a moisture barrier or capillary break between the bales and their supporting platform. Bale walls can be tied together with pins of bamboo, rebar, or wood (internal to the bales or on their faces), or with surface wire meshes, and then stuccoed or plastered, either with a cementbased mix, lime-based formulation, or earth/clay render. The bales may actually provide the structural support for the building ("load-bearing" or "Nebraska-style" technique), as was the case in the original examples from the late 19th century.

This straw bale house plastered withloam is located in Swalmen, in the southeastern Netherlands Alternatively, bale buildings can have a structural frame of other materials, usually lumber or timber-frame, with bales simply serving as insulation and plaster substrate, ("infill" or "non-loadbearing" technique), which is most often required in northern regions and/or in wet climates. In northern regions, the potential snowloading can exceed the strength of the bale walls. In wet climates, the imperative for applying a vapor-permeable finish precludes the use of cement-based stucco commonly used on load-bearing bale walls. Additionally, the inclusion of a skeletal framework of wood or metal allows the erection of a roof prior to raising the bales, which can protect the bale wall during construction, when it is the most vulnerable to water damage in all but the most dependably arid climates. A combination of framing and load-bearing techniques may also be employed, referred to as "hybrid" straw bale construction.[12]

Straw bale construction Straw bales can also be used as part of a Spar and Membrane Structure (SMS) wall system in which lightly reinforced 2" - 3" [5 cm - 8 cm] gunite or shotcrete skins are interconnected with extended "X" shaped light rebar in the head joints of the bales.[13] In this wall system the concrete skins provide structure, seismic reinforcing, and fireproofing, while the bales are used as leave-in formwork and insulation. Typically "field-bales", bales created on farms with baling machines have been used, but recently higher-density "precompressed" bales (or "straw-blocks") are increasing the loads that may be supported. Field bales might support around 600 pounds per linear foot of wall, but the high density bales bear up to 4,000 lb./lin.ft., and more. The basic bale-building method is now increasingly being extended to bound modules of other oft-recycled materials, including tire-bales, cardboard, paper, plastic, and used carpeting. The technique has also been extended to bags containing "bales" of wood chips or rice hulls.[3][4] Straw bales have also been used in very energy efficient high performance buildings such as the S-House[14] in Austria which meets the Passivhaus energy standard. In South Africa, a five-star lodge made from 10,000 strawbales has housed luminaries such as Nelson Mandela and Tony Blair[15]. In the Swiss Alps, in the little village of Nax Mont-Noble, construction works will start in 2011 for the first hotel in Europe built entirely with straw bales.[16]

There are two main types of strawbale construction: loadbearing and nonloadbearing. In loadbearing strawbale construction, which is also known as Nebraska-style because it was originated in the 19th century by pioneers in the Nebraska Sandhills, the bales hold the weight. Although more traditional, this type of strawbale construction is more unusual because it is harder to maintain structural integrity. In a poorly constructed loadbearing strawbale house, the straw might begin to compress over time, damaging the walls and roof. Non-loadbearing construction is also known as post-and-beam, and is more similar to conventional building methods. A frame of wood or other materials is constructed and the bales are placed in the walls as filler.This is the easier and more common type of strawbale construction. A thick layer of plaster is used to finish the walls of both types ofstrawbale house.

Straw: A Renewable Resource Straw, the stalks remaining after the harvest of grain, is a renewable resource, grown annually. Each year, 200 million tons of straw are under utilized or just wasted in this country alone. Wheat, oats, barley, rice, rye, and flax are all desirable straws for bale walls. Even though the early bale homes used hay for the bales, hay is not recommended because it is leafy and easily eaten by creatures great and small. Straw, tough and fibrous, lasts far longer. Straw-bale expert Matts Myhrman estimates that straw from the harvest of the United States' major grains could be used to construct five million, 2,000 square-foot houses every year! More conservative figures from the U.S. Department of Agriculture indicate that America's farmers annually harvest enough straw to build about four million, 2,000 square-foot homes each year, nearly four times the houses currently constructed. Building a straw-bale house is relatively simple. A basic 2,000 square-foot house requires about 300 standard three-wire bales of straw (costing approximately $1,000). Placed on a foundation, the bales are skewered on rebar pins like giant shiskabobs. After wiring and plumbing, the walls are sealed and finished. Because grains are grown in almost every region of the country, straw bales are readily available, with minimal transportation costs. Lumber from trees, in addition to becoming more scarce and expensive, must be transported over longer distances. TYPES OF STRAW BALES Straw bales come in all shapes and sizes, from small two-string bales to larger three-string bales and massive cubical or round bales. The medium sized

rectangular three-string bales are preferred for building construction. Three-string bales are better structurally, have higher R-value, and are often more compact. A typical medium-sized, three-wire bale may be 23" X 16" X 42" and may weigh from 75 to 85 pounds. The smaller two-wire bales, which are easier to handle, are roughly 18" X14" X 36" and weigh 50 to 60 pounds. If the current trend continues, it may not be long before "construction-grade" bales begin to appear. METHODS OF BUILDING WITH STRAW Straw has been used for centuries by builders who recognized its structural integrity. A piece of straw is simply a tube made of cellulose. Tubes are recognized as one of the strongest structural shapes. Straw was first used to reinforce mud against cracking. A lattice of straw criss-crossing a layer of mud produced a surface that remained crack free for decades, or in many cases, centuries. With the late 19th century invention of the baler, builders were given a convenient new building block, the rectangular bundle of straw. Straw-bale building in the United States has been mostly structural (Nebraska-style) and non-structural. Pliny Fisk III of the Center for Maximum Building Potential in Austin, Texas, describes the following five methods of building with straw. 1. In-fill or non-structural bale - This building system, useful for construction of large structures, depends on a pole or post-and-beam building design. Post-andbeam construction employs a skeleton of vertical posts and horizontal beams to support the roof. The straw-bale walls have only themselves to support. The bales are attached to each other by piercing the bales with rebar or bamboo and attaching the bales to the pole or column. Fisk's Center has completed three buildings totaling 4,500 square-feet of space using this method. 2. Structural bale - Automatic straw balers create tight building blocks that are stacked up to one and one-half stories. The "Nebraska-style" buildings originated on the Great Plains where structural wood was not available. Bales are stuccoed on the exterior and plastered on the interior to protect them and provide an attractive finish. The stucco and plaster add to the structural integrity of the wall system. 3. Straw-clay building - A pancake like batter of clay and water stirred into the loose straw produces a straw-reinforced clay mud. In the past, this mixture was packed into a double-sided wood form between the posts and beams of a timberframe building. Today, a light weight wooden ladder like frame replaces the old heavy timber frame. European heavy timber structures using this method are still standing after more than 200 years. This method has passed the most stringent European fire codes.

4. Mortar bale - Structural mortar, made of portland cement and sand, is applied between the straw bales. When dry, its lattice structure remains intact if the straw bales should ever fail. This method, developed in Canada, passes Canadian building codes. Bales are stuccoed on the exterior and plastered on the interior to protect them and provide an attractive finish. The mortered joints, stucco, and plaster also add to the structural integrity of the wall system. 5. Pressed straw panels - Straw is compacted under certain temperatures. The resulting panels are 100 percent straw that can be used to build pre-fabricated structures, not only walls, but also roofs and floors.

FIRE RESISTANCE
Fire resistance We would have liked to do our own test to compare strawbale with brick veneer but we were not able to get suitable equipment, so we researched tests done by other people. Straw bale buildings are extremely hard to burn. This is because the bales hold enough air for good insulation but because they are compacted tightly they don‟t hold enough air to permit combustion. *The National Research Council of Canada tested plastered straw bales for fire safety and found them to perform better than conventional building materials. In fact, the plaster surface withstood temperatures of about 1,850° F for two hours before any cracks developed. According to the Canada Mortgage and Housing Corporation, "The straw-bales/mortar structure wall has proven to be exceptionally resistant to fire. The straw bales hold enough air to provide good insulation value, but because they are compacted firmly, they don't hold enough air to permit combustion." *In 1993 the New Mexico Straw Bale Construction Association commissioned SHB Agra to test strawbale walls for fire resistance. The tests showed that such walls are fire tolerant to the point where they were included in the New Mexico building Code. A video of the tests is titled „Building with Straw Vol 3 : Straw Bale Code Testing Black Range Films Box 119 Kingston, New Mexico. Australian Bushfire Test Results SHB Agra's Report on Fire Testing In 1993, as part of the testing commissioned by the New Mexico-based Straw Bale Construction Association which eventually led to the inclusion of straw bale in the

New Mexico building code, fire testing was undertaken on a straw bale wall panel by SHB Agra, Inc. Transmission of heat through the unreinforced [unplastered] straw bale during its test was not sufficient to raise the average temperature at the exterior face of this wall to 250F above the initial temperature (the governing criteria for ASTM E-119). The highest average temperature recorded on the unexposed face of the unreinforced straw was 52.8F at thirty minutes. Transmission of heat through the wall did not exceed the allowable limit for any single thermocouple. Additionally, there was no penetration of flames or hot gases through the unre-inforced straw bale wall during the thirty minute test. The burning characteristics of the unreinforced straw bales were observed through observation ports during the test. The test panel was also examined after it was removed from the combustion chamber. The straw was observed to burn slowly and the charred material tended to remain in place. The residual charred material appeared to protect the underlying straw from heat and ventilation, thereby delaying combustion. The maximum temperature recorded inside the furnace was 1,691F at thirty minutes. Upon removal, the bales did. not burst into flames, but slowly smouldered. The fire was easily extinguished with a small quantity of water. After the unplastered bales passed the 30 minute fire test, plastered bales were tested more closely simulate real-life burning characteristics on finished walls, with the following results: The highest temperature recorded on the exterior face of the stuccoed straw bales after 120 minutes of exposure was 63.1F, less than a 10 degree rise in temperature. The highest average furnace temperature recorded during this period was 1,942F, however at least one thermocouple recorded temperatures exceeding 2,000 F. There was no penetration of flames or hot gases through the stuccoed straw bale wall. The burning characteristics of the stuccoed straw bales was also observed. The reaction consisted of initial cracking of the stucco surface as the heat was applied, with little other evidence of distress." Fire retardants Where exceptional fire risks exist (eg bushfire areas) some very conservative Australian officials insist that since no Australian standard exists proving the fire resistance of straw bale construction, extra precautions need to be taken. One can use fire resistant foil which satisfies such regulators. This is placed on the outside of the wall before the wire netting and plaster layers. Possibly also a fire retardant mixture could be used. Solomit ceilings which have been used in Australian buildings since the 1940‟s incorporate such a mixture. One mixture is 2 parts by volume Borax to 1 part of granular Boric Acid. Mix with warm water till no more will dissolve. Soak straw in the solution and dry in the sun. This also prevents the development of any fungi. A built wall can also be sprayed with

a fairly high pressure jet of the solution before rendering with plaster. Knowing how quickly brick veneer houses burn and the need for smoke alarms in modern houses suggests to us that a strawbale house would be a much safer place to live. In SA there has been one case of vandalism where a pile of dry hardwood planks was stacked against the wall of a strawbale building in Whyalla and lit up. The fire was in an isolated place with no one there to raise the alarm. The fire went out by itself having burned for some hours, leaving minor damage to the wall. A brick veneer home would have almost certainly burned to the ground.

MOISTURE: Building with highly variable natural materials could be a daunting prospect, but we do it all the time. For example, wood is used for structural and decorative uses, building standards are written for it, strengths are often assumed, and we are so used to doing this we have few qualms. Humans have been working with wood since they first picked up a twig or branch possibly hundreds of thousands of years ago. Despite this very long history of association with the material, it is amazing how often we can still get timber usage wrong. The latest evidence of this is currently occurring in New Zealand with low durability timber rotting under supposedly impervious claddings. This crisis follows the similar leaky buildings disaster that occurred in Canada a few years ago. Subsoils are also highly variable naturally occurring materials, and millions of earth walled buildings have been erected around the world over the last ten thousand years at least. Even so there are not many countries with any systematic standardisation for unfired earthen materials. New Zealand is, as far as I know, the only country in the world with a comprehensive suite of earth building standards that meet the requirements of a modern performance based building code. In New Zealand, earth has a performance history of at least 150 years and now enjoys the same status as timber, concrete masonry, and steel as a “codified” building material. Cereal crop stems and other plant fibres and leaves have been used in parts of buildings for centuries. Generally their use was non-structural and often required

frequent replacing. Once machinery made possible the manufacture of bales or blocks out of straw they have seen limited use as the structural component of walls for one hundred years or so in some dry climates. Recently the use of such materials has spread into other climatic zones, often taken up by people whose imagination has been captured by the thought of easy, cheap, (and beautiful) buildings. Despite the enthusiasm there are few guidelines on how to design and build with these materials so that they meet the provisions of modern building codes, especially in temperate humid climates with strong wind driven rain such as occurs in many parts of New Zealand. As Chair of the Standards New Zealand/Standards Australia Joint Technical Committee for Earth Building (BD 083), I rejected an approach made around 1996 to enlarge our work to write strawbale standards for Australasia, despite the wide range of building methods that utilise both earth and straw. The rejection was based on several reasons:
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Earth buildings rely on the binding properties of clay. Once this is absent, then you have another material and set of “rules”; Strawbale was relatively recent in New Zealand and Australia and did not have a large number of local examples or performance history to draw upon; There was no adequate funding available to enable us to do the work. As a largely volunteer committee we had more than enough to do to get the earth building standards written. In the end, as it turned out, the New Zealand Earth Building Standards (Ref 1)were published in 1998, and only now has Standards Australia published an Earth Building Handbook, (Ref 2) which falls well short of being a Standard. Some members of the committee had no experience or interest in strawbale.

It is still my opinion that in New Zealand at least (and I suspect in Australia) there simply is not a long enough history of building in strawbale to enable a Standard to be written that can ensure adequate performance. However, if we were to contemplate such a Standard for a climate such as New Zealand‟s, what would be the starting point for durability performance criteria? I think that the short answer is simple.


A strawbale building must be designed and constructed in such a manner that the straw always remains dry throughout the entire building process and the lifetime of the building.

The suggestions that follow are derived from the experience dealing with the design and construction of earth walled and strawbale buildings in New Zealand, observation of some strawbale failures and successes, together with thoughts gleaned from colleagues and literature. I consider strawbale buildings to be very demanding technically, and must be responsive to regional and local conditions, especially climatic ones. However, there are significant environmental advantages from using non-toxic natural materials to create highly insulated buildings that will have low energy consumption over its life (Ref 8). These comments do not detail how to achieve desirable outcomes, nor do they consider every strawbale construction technique. There will not be an international one-style-fits-all, and unabashed regionalism will prevail. This is up to the skill and experience of the designers involved. Rather I canvas some of the issues required for moisture control, acknowledging that many of these issues require more work to be done before definitive recommendations can be made. A starting point for me is that strawbales are an extremely moisture-sensitive wall material. If they get soaked the tightly bound hollow straw fibres are capable of absorbing and holding a great amount of water. Before they can dry out they can remain wet for long enough for fungal decay to start if in a temperate climate with high humidity. Plasters leak and water repellent treatments fail. Therefore successful straw bale design relies on keeping the straw bale wall out of the reach of the weather. Then, any moisture that reaches the bale walls is readily dispersed with freely breathing surfaces. All sources of moisture must be considered, whether it be external (rain, flood, mist, fog, humidity, etc), internally generated moisture (cooking, bathing, washing, condensation, respiration etc), or the dynamic movement of water vapour through and within the strawbale wall, surface coatings, and cladding system. The strawbales must be baled, transported, stored, supplied, installed and kept dry (moisture content below 18%) - forever. Building site selection (Apart from usual considerations of location, stability, access, and orientation)

Surface water or flooding must not be able to reach the base of strawbale walls. The site will be sunny and get some air movement to keep the exterior dry. Ideally there will be shelter from wind-driven rains. Primary Weather Protection.
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“Good hat”. Design and build the roof structure so that it can be built first, especially given the unpredictable nature of New Zealand‟s climate. If the site is too exposed for the walls to be protected by roof overhang alone, design a rain-screen cladding system. Design primary weather protection to ensure adequate mechanical deflection of wind driven rain off strawbale walls. One obvious way of doing this is by the provision of eaves or roof overhangs to all strawbale walls.

Firstly, assess the site for exposure to wind-driven rain as it affects the strawbale walls. Determine if the wind zone is Low, Medium, High, Very High, or Specific Design. NZS 4299 (Ref 1)defines these zones as the design wind speed at ultimate limit state of 32, 37, 44, 50, and >50m/s respectively. Work out the exposed wall height (the vertical height of the strawbale wall from the top of the footing to the lower edge of the roof overhang) and calculate the necessary roof overhangs. As a rough start towards this some of my colleagues and myself (Ref 3) have advocated that in Low wind zones the ratio of roof overhang to exposed wall height should be 3:4, and for Medium wind zones this should be 1:1. In other words, forget eaves - use full verandahs. I think that this level of primary weather protection is about right and recognises that moisture sensitivity of strawbale walls to external moisture is around one order of magnitude greater than any other common building materials. It should be possible to fine-tune this approach as Driving Rain Indices become developed (Ref 5). For strawbale building we should be aiming for a table or matrix that factors in wind zone, rainfall, driving rain indices, exposed wall heights and roof overhang distances, but more research is required before this could be completed.

The leaky building crisis in New Zealand has recognised the benefit of roof overhangs for rain deflection (Ref 6) and the NZ Earth Building Standard NZS 4299 Amendment #1 (Ref 1) already does this in Table 2.4 that relates site exposure to a ratio of eaves height to eaves width.
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“Good boots” Keep the base of the wall away from wet ground.

To help prevent rising damp and splashing keep the base of the strawbales at least 350 mm above finished ground level or 250mm above a permanently paved strip around the base of the walls that will keep moisture and plants away. Water proof the top of the footing and do not bridge the damp proof course, taking special care here with plaster (Ref 3). Secondary weather protection


Plaster coats directly onto strawbale should not be regarded as primary weather protection. They leak.

Only buildings that have a wind exposure of Low or Medium are suitable for single thickness plastered straw bale wall construction, and then only with the very generous overhangs suggested in these guidelines to protect the straw bales walls. The plaster must be durable enough to withstand the weather conditions they will encounter, and help deflect and drain away any water that gets past the primary rain protection. Ensure plaster coats do not bridge any damp proof course. They need to be freely breathable to allow the easy passage of water vapour, and not trap water behind them. They also must not be cracked or have holes in them that allow the entry of water. For success they need to be placed over a tightly compressed wall structure. Pinning of bales is not enough, and vertical pre-compression of the walls before plastering is essential. This considerably stiffens up the structure, and helps prevent creep of the plaster substrate, with consequent failure. Lime plasters (three coats) appear to be ideal. They adhere well to straw and do not seem to require reinforcing mesh although hair or its modern equivalent of polypropylene fibre helps. Lime plasters are durable, are not too brittle, do not crack readily, are self-healing from small cracks, breathe well, and look good! Any surface decorative coating must be free breathing.

Window/door openings must be very carefully designed with good heads, jambs and sill flashings. These must not leak, either from direct water penetration, soakage through materials, or by capillary action. They must also cast any rain that might get past the generous roof overhangs to the outside of the wall surface. Windowsills in particular, especially with rebated windows, can be very tricky areas. For sites outside Low or Medium exposure (ie. sites with High, Very High, or Specific Design wind zones), or with less roof overhang than suggested above require a modified approach. Strawbales, (if used at all), should be placed behind a weather durable and resistant skin that incorporates a pressure equalised, ventilated, vermin proof cavity that drains to the exterior. The precise design of such wall cavities is currently undergoing review in New Zealand as a result of a leaky buildings crisis (Ref 7). The strawbales behind the cladding should be encapsulated in a breathing plaster such as lime or earth, and the cladding and cavity must be designed and built to prevent water crossing the cavity to get to the strawbales. Alternatively the site needs to be modified to protect the walls with trellises, shelter trees, earth mounding, fences or some other form of permanent shelter (ie shelter that will be there for at least the life of the straw bale walls) Interior moisture The high insulation value of strawbale walls will help prevent condensation occurring on walls. Windows, especially if not double-glazed, may get condensation on them and this needs to be collected and channelled so that it cannot get into the strawbales. Provide a damp-proofed toe up of at least 50mm above the floor to keep the base of the walls safe from any internal flooding eg washing machine leak, or sitting water if the roof is not built first. Passive solar design allows sun into the building, especially in winter, to help keep the interior warm and dry with adequate heating and ventilation. Strawbale walls in “wet areas” such as bathrooms, laundries and kitchens need to be carefully thought about to ensure that they will not be subjected to excessive internal moisture build up. Splash areas such as showers or behind basins and taps need to be waterproofed and given impervious surfaces.

Any “wet area” should incorporate floor drains to prevent flooding saturating the bottom of the wall which will of course be on permanent toe-ups above finished floor level with no possibility of moisture bridging upwards past DPCs through plaster finishes or other means. Dynamic movement of water vapour To help control water vapour moving into the strawbale walls, encapsulate all straw to ensure that the walls are not exposed to the atmosphere anywhere, even behind cavities or the tops of walls. As warm moist air migrates from the interior towards the cold exterior the dew point can be reached. Clay based plasters help absorb water vapour from the air and dry it out before it can migrate into the strawbale walls. Earth plasters are only suitable for interior surfaces. A high humidity absorbent plaster can be made from perlite and bentonite clay and this could warrant further research. (Ref 4). Cement based plasters are too dense for easy breathability. They are also brittle and tend to crack. My experiments suggest that gypsum plasters, although breathable, provide a more highly heat conductive surface than earth plaster surfaces and might be more prone to interior mould growth. Freely breathing surfaces will allow the exit of any water vapour that does get into the walls preventing it from getting trapped and reaching excessive limits. It will help if there are no materials with high heat conducting coefficients or that can form thermal bridges within the strawbale walls for water to condense onto eg steel pins, posts, or water pipes. Insulate the strawbale wall from any cold bases eg concrete, with non-absorbent insulating materials resistant to compression. These could form part of the toe up to prevent thermal bridging or possible condensation at this point. Do not run water pipes within strawbale walls, not only because of a possible point for condensation to occur on, but also in case of leaks. Seal around all penetrations in the plaster to maintain the encapsulation of the straw.

Maintenance Regularly look over the building for any signs of damage, leaks, or failure, including the roofing, guttering, downpipes, plaster and cladding. Maintain the surface as necessary, and check that soil or plants have not breached ground clearances. Check for vermin damage and counter rats, mice, ants, snails, etc. Conclusion By keeping strawbale in walls dry, durable and beautiful buildings can be erected. Then the significant environmental benefits to be gained from highly insulated low energy consumption buildings can be realised using strawbales.

TERMITE TREATMENT: Non Toxic Termite Control DEFINITION CONSIDERATIONS COMMERCIAL IMPLEMENTATION GUIDELINES 1. 2. 3. 4. 5. Prevention Sand Barriers Metal Termite Shields Monitoring, Detection and Identification Termite Treatment

STATUS ISSUES

DEFINITION: Non-toxic termite control is the use of termite prevention and control without chemical use. Instead, physical controls are installed during construction such as sand barriers or metal termite shields. If termite infestation does occur, least toxic methods of treatment are used.

CONSIDERATIONS: Most areas of Texas have termites. These include subterranean termites that live in the soil and drywood termites that attack dry wood. According to the Texas Agricultural Extension Service, there is a greater than 70 percent probability that wooden structures in Texas will be attacked by termites within 10 to 20 years. Termite problems within one year after construction have been reported. When wood is used as a building material, termite prevention in the form of treated wood or naturally resistant wood will be required by building codes. Typically, chromated copper arsenate (CCA) pressure-treated wood is used. Two alternative chemical substances have gained popularity as more toxic substances such as chlordane have been banned for soil treatment. These include organophosphates and pyrethroids. However, these chemicals are toxic to people as well as termites, and can offgas and leach out into the soil and water table. They can be absorbed through the skin, lungs and through ingestion. Exposure to small children, workers, chemically-sensitive individuals and animals can lead to serious health problems. Less toxic wood treatments are available. (See Wood Treatment Section.) However, alternatives to wood treatment and chemical treatment can be quite effective. Least-toxic strategies must be used in combination to achieve maximum effectiveness. Few pest control managers expect non-toxic methods to completely replace chemical use. However, they offer considerable potential for the reduction of chemical use, and may prevent such use in all but extreme situations.

COMMERCIAL STATUS TECHNOLOGY: Research and monitoring is underway to test the effectiveness of non-toxic termite prevention techniques. The USDA Southern Forest Experiment Station in Gulfport, Mississippi, and the University of Hawaii are doing research. Successful laboratory results have been obtained with the use of properly designed sand barriers. Pest control professionals in California have adapted and tested sand barriers with good results. Some studies in California have found some physical barriers to be 15% more effective than chemical treatments.

SUPPLIERS: There are architects and pest management companies in Austin that can provide expertise and services in non-toxic termite prevention and control. However, not all professionals currently have knowledge or experience with non-toxic termite control. COST: Initial costs of non-toxic termite prevention may be 25% higher than chemical controls. However, these costs may be offset due to the long term nature of structural solutions. In addition, cost offsets can occur if traditional fill material is replaced with sand or cinder barriers, preventing the need for termiticides.

IMPLEMENTATION ISSUES FINANCING: Lenders will typically look for traditional methods for the prevention of termites, such as the use of treated wood. Educating lenders about the effectiveness of nontoxic prevention measures and encouraging financing incentives for their use is a goal of the Green Builder Program. PUBLIC ACCEPTANCE: For successful termite prevention using non-toxic methods, education and cooperation between the professional and the resident/owner will be necessary. Increased monitoring after construction will be necessary. REGULATORY: Building codes (such as Section R-310 of the CABO One and Two Family Dwelling Code) call for protection by chemical soil treatment, pressure-treated wood, naturally termite-resistant wood (such as heartwood of redwood and eastern red cedar), or physical barriers approved by the building official in areas with subterranean termites. Approved combinations of methods may be used. For decay prevention, any wood (siding, trim, framing) within 6 inches of the finished grade must be protected. Additionally, wood girders within 12 inches, wood structural floor within 18 inches, and wood sills on masonry slabs within 8

inches must also be protected. Decay prevention and termite protection are addressed jointly with wood treatment and naturally resistant wood. Structural controls for termites such as sand barriers and termite shields will not eliminate the need for decay prevention in wood within the distances from the ground mentioned above. The Honolulu building code was rewritten in 1991 to include the use of sand barriers instead of chemical controls. The City of Austin will examine precedents accepted by other jurisdictions on a case-by-case basis.

GUIDELINES Any pest management program that uses the principles of Integrated Pest Management (IPM), or least toxic methods, will have the following components:
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Integration of least-toxic treatment methods and materials; Monitoring; Detection and identification.

No method of termite treatment can be assumed to be 100% effective. In homes with wood as a construction material, regular inspections should be performed, regardless of treatment and prevention methods. The best method is non-toxic prevention, however there are also non-toxic treatment methods if termites are found. 1.0 Prevention The only sure prevention of termite problems is the use of building materials other than wood. However, if wood is used, there are preventative measures available to the builder other than chemical treatments and treated wood products. A common tree in Austin known to resist termites is the familiar mountain cedar (actually a member of the juniper family). Although not commercially lumbered, natural cedar posts have traditionally been used as foundation piers on old structures, and extensively for fences and furniture. The use of juniper wood has some potential for application as a termite and insect resistant wood.Eliminating sources of chronic moisture in the home is one of the most important factors in managing subterranean termites, carpenter ants, and some wood boring beetles. Moist soil is necessary for termites to survive. Termites travel back and forth between soil and food sources because they must obtain moisture from the soil. In addition, capillary

action and water vapor buildup can result in excessive dampness which can actually wick through a concrete slab or masonry foundation to the wood framing above it, thus attracting termites. In above-ground foundations, moisture barrier films such as 6 mil polyethylene can be used to cover the area under the structure. This will help decrease moisture buildup in sub-flooring. Foundation wall vents should be placed to provide cross ventilation for homes with crawl spaces. If re-grading or remodeling covers vents, additional vents may be needed. Some experts recommend the use of moisture barriers under slab foundations as well. Soil should always be from 6 to 18 inches below any wood member, the greater the distance, the better. Good siting and drainage design will help to prevent moisture buildup in and around the structure. All exterior grades should slope away from the structure to provide drainage. Porches and features such as planter boxes should be constructed and sealed to prevent moisture and soil contact with the structure. Exterior landscaping should not cause moisture build-up around the foundation. A small air space should be retained between plant leaves and walls to prevent moisture and mold build-up. Automatic irrigation heads should be properly aligned or shielded to prevent direct spray onto the building. Areas subject to moisture build-up, such as bathrooms, should be given special attention since they are likely to be attack areas. Areas under tubs and drains leading to the exterior (such as air conditioner drains) should be considered vulnerable spots. All wood-to-soil and wood-to-concrete contacts should be eliminated for fence and deck posts, rail supports, and trellises etc. Posts should be placed in metal holders (commercially available). Even treated deck piers may not deter termites since they may bypass the treated piers to reach untreated decking above. All wood subject to moisture, especially exterior wood, should be properly sealed. Exterior windows, even if under an overhang such as a porch, should be completely moisture sealed. Exterior siding, especially along the bottom wall edges, should be completely moisture sealed on all exposed surfaces. All lumber scraps, wood debris and stumps should be removed from the site after construction is complete. Backfill under a foundation should never contain wood scraps, and scrap should never be left in crawlspaces or under foundations. Such scraps are invitations to termites to eat first the scrap and then move on to the main structure.

2.0 Sand Barriers Sand barriers for subterranean termites are a physical deterrent because the termites cannot tunnel through it. Sand barriers can be applied in crawl spaces under pier and beam foundations, under slab foundations, and between the foundation and concrete porches, terraces, patios and steps. Other possible locations include under fence posts, underground electrical cables, water and gas lines, telephone and electrical poles, inside hollow tile cells and against retaining walls. Sixteen grit sand or cinder is placed in a 20-inch band on the soil surface or in trenches next to foundation walls. The sand layer should be 4 inches thick at the foundation, and feathered out to meet grade at the outer edge of the 20-inch band. For trench installations, trenches should be 4″ deep and 6″ wide. Some integrated pest management experts have developed a machine, called a sand pump, that blows sand under the house. For sand barriers around the outside perimeter of a foundation, they recommend a sand trench in order to avoid disturbance of the sand. In addition, a cap made of masonry or other materials may be recommended to protect the barrier from gardening, animals, etc. Tamping of sand can be done to increase impermeability to termite attack. 2.1 Slab Barriers Termites can easily pass through small cracks, as small as 1/32″, which may occur in slab foundations. For sand barriers in conjunction with slab foundations, the sand or cinder must be applied before the foundation is poured. Installing the sand layer of the appropriate mesh size followed by a layer of coarser gravel for grading to the desired level has worked well. To cut costs, sand treatments may be installed in particularly vulnerable areas of the slab, such as around pipe penetrations, as opposed to under the entire slab. Costs for cinder fill under a slab can often be competitive with the costs of standard fill and the initial chemical termite treatment. 2.2 Sand Selection The size of sand particles is critical to the success of sand barriers. Sand or grit size should be no larger or smaller than that able to sift through a 16-mesh screen. Sand smaller than 16-grit can be carried away by termite workers; larger sand can support tunnel construction by termites. If the sand to be used has some particles

smaller than 16-mesh size, sand can be screened with mesh of the appropriate size. Certain grades of sandblasting sand which come in bags may be suitable for barriers. Crushed volcanic cinder of the appropriate size is recommended by some experts. 2.3 Performance Sand barriers can also be used to repair seals that have become broken between foundations and other building elements such as porches. Such settling and breaking of “cold” joint seals can occur due to subsidence and temperature extremes. In laboratory tests, sand was shown to retain its “seal” against structural members after movement similar to earthquakes. Although earthquakes are not a problem in our area, soil movement and settling due to expansive soils is often a problem. Use of sand barriers is still experimental, and must be followed with postinstallation as well as regular inspections. Sand barriers may cost 25 % more than conventional chemical treatments, however the physical barrier will provide long term protection. Chemical prevention is normally guaranteed for only one year, and introduces toxins into the home environment. 3.0 Metal Termite Shields Metal termite shields are physical barriers to termites which prevent them from building invisible tunnels. In reality, metal shields function as a helpful termite detection device, forcing them to build tunnels on the outside of the shields which are easily seen. Metal termite shields also help prevent dampness from wicking to adjoining wood members which can result in rot, thus making the material more attractive to termites and other pests. Metal shields are used in conjunction with concrete or solid masonry walls, and are fabricated of sheet metal which is unrolled and attached over the foundation walls. The edges are then bent at a 45 degree angle. Metal shields must be very tightly constructed, and all joints must be completely sealed. Any gaps in the seals will allow an entry point for termites. Joints may be sealed by soldering, or with a tarlike bituminous compound. Metal flashing and metal plates can also be used as a barrier between piers and beams of structures such as decks, which are particularly vulnerable to termite attack.

4.0 Monitoring, Detection and Identification The Bio-Integral Resource Center (see Resources, General Assistance) recommends the following steps: 1. 2. 3. 4. 5. 6. Monitor the building at least once per year. Identify the species of termite. Correct structural conditions that led to the infestation. Apply physical or biological controls. Spot treat with chemicals if necessary. Check for effectiveness and repeat if required.

Regular termite monitoring should be done with a plan of the structure in hand. This will help to identify inaccessible areas that may be hard to spot with a visual inspection. Annual or bi-annual inspections are recommended. Subterranean termites build characteristic mud tubes for movement between nests. The appearance of these tubes are often the first sign of infestation. Detection can become difficult if such tubes are hidden inside walls, or termites are entering in cracks occurring in concrete slabs or foundations. Dogs are being used by some individuals to aid in termite inspection. These dogs are trained to detect termites and other wood damaging insects, and can provide information about inaccessible areas of the structure. Their keen sense of smell coupled with their ability to wriggle into areas too small for human access can make the dog-assisted inspection a valuable tool. 5.0 Termite treatment The first step in any termite treatment is accurate identification of the species. Next, location of nests must be found. Next, selection of a combination of least toxic strategies and tactics is necessary. When selecting a pest management company, be sure to choose a reliable firm. Texas law requires commercial pesticide applicators to be certified. Check for certification documentation, references, and work experience, or check with the Structural Pest Control Board of Texas. Ask if the company practices integrated pest management techniques, or has an experimental license which may be necessary for some alternative techniques.

Non-toxic treatments include use of nematodes (microscopic worms), especially for chemically-sensitive individuals or environmentally-sensitive areas. Nematodes are pumped into the infested area, where they will kill the insects. Boric acid bait blocks can be placed around the structure, where they will attract the pests to consume termiticides without broad application of chemicals. Drywood termites can be treated with thermal, freezing, or electrical eradication techniques. Desiccating dusts, non-toxic substances resulting in pest dehydration and death, have also been used successfully on drywood termites. These treatments can be combined with others, such as installing metal shields (if they have not been used previously), sealing of broken seals or open areas, and regrading of soil outside the foundation to improve drainage or create a gap between soil and wood areas such as siding. In addition, termites can be physically removed by trapping or nest excavation.

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