straw as a building material

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    BASIC:

    Straw, grass, and reeds have been used as building materials for centuries. Strawhouses have been built on the African plains since thePaleolithic. Straw bales wereused in construction 400 years ago in Germany; and straw-thatched roofs have

    long been used in northern Europe and Asia. In the New World,teepeeswereinsulated 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, whichwas invented in the 1850s and was widespread by the 1890s.[6]It provedparticularly useful in theNebraska Sandhills. Pioneers seeking land under the1862Homestead Actand the 1904Kinkaid Actfound a dearth of trees over muchof Nebraska. In many parts of the state, the soil was suitable fordugoutsandsodhouses.[7]However, in the Sandhills, the soil generally made poor constructionsod;[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 aschoolhouse 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, buildersbegan plastering their bale structures; if cement or lime stucco was unavailable,locally obtained "gumbo mud" was employed.[9]Between 1896 and 1945, anestimated 70 straw-bale buildings, including houses, farm buildings, churches,schools, offices, and grocery stores had been built in the Sandhills.[6]In 1990, ninesurviving bale buildings were reported inArthurandLoganCounties,[10]including

    the 1928Pilgrim Holiness Churchin the village ofArthur, which is listed intheNational Register of Historic Places.[8]

    Since the 1990s straw-bale construction has been substantially revived, particularlyin North America, Europe and Australia.[11]

    [edit]Method

    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struction#cite_note-laststraw-8http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-laststraw-8http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-nomform-7http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-custersurvey-6http://en.wikipedia.org/wiki/Sod_househttp://en.wikipedia.org/wiki/Sod_househttp://en.wikipedia.org/wiki/Dugout_(shelter)http://en.wikipedia.org/wiki/Kinkaid_Acthttp://en.wikipedia.org/wiki/Homestead_Acthttp://en.wikipedia.org/wiki/Sand_Hills_(Nebraska)http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-viable-5http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-viable-5http://en.wikipedia.org/wiki/Tipihttp://en.wikipedia.org/wiki/Paleolithic
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    Straw bale building typically consists of stacking rows of bales (often inrunning-bond) on a raised footing orfoundation, with a moisture barrier or capillary breakbetween the bales and their supporting platform. Bale walls can be tied togetherwith pins ofbamboo,rebar, orwood(internal to the bales or on their faces), orwith surface wire meshes, and thenstuccoedorplastered, either with acement-basedmix, lime-based formulation, or earth/clay render. The bales may actuallyprovide 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 withloamis located inSwalmen, in thesoutheasternNetherlands

    Alternatively, bale buildings can have a structural frame of other materials, usuallylumber or timber-frame, with bales simply serving as insulation and plastersubstrate, ("infill" or "non-loadbearing" technique), which is most often required innorthern regions and/or in wet climates. In northern regions, the potential snow-

    loading can exceed the strength of the bale walls. In wet climates, the imperativefor applying a vapor-permeable finish precludes the use of cement-based stuccocommonly used on load-bearing bale walls. Additionally, the inclusion of askeletal framework of wood or metal allows the erection of a roof prior to raisingthe bales, which can protect the bale wall during construction, when it is the mostvulnerable to water damage in all but the most dependably arid climates. Acombination offramingand load-bearing techniques may also be employed,referred to as "hybrid" straw bale construction.[12]

    http://en.wikipedia.org/wiki/Brickwork#Stretcher_bondhttp://en.wikipedia.org/wiki/Brickwork#Stretcher_bondhttp://en.wikipedia.org/wiki/Brickwork#Stretcher_bondhttp://en.wikipedia.org/wiki/Brickwork#Stretcher_bondhttp://en.wikipedia.org/wiki/Foundation_(architecture)http://en.wikipedia.org/wiki/Foundation_(architecture)http://en.wikipedia.org/wiki/Foundation_(architecture)http://en.wikipedia.org/wiki/Bamboohttp://en.wikipedia.org/wiki/Bamboohttp://en.wikipedia.org/wiki/Bamboohttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Stuccohttp://en.wikipedia.org/wiki/Stuccohttp://en.wikipedia.org/wiki/Stuccohttp://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Cementhttp://en.wikipedia.org/wiki/Cementhttp://en.wikipedia.org/wiki/Cementhttp://en.wikipedia.org/wiki/Cementhttp://en.wikipedia.org/wiki/Load-bearinghttp://en.wikipedia.org/wiki/Loamhttp://en.wikipedia.org/wiki/Loamhttp://en.wikipedia.org/wiki/Swalmenhttp://en.wikipedia.org/wiki/Swalmenhttp://en.wikipedia.org/wiki/Swalmenhttp://en.wikipedia.org/wiki/Netherlandshttp://en.wikipedia.org/wiki/Netherlandshttp://en.wikipedia.org/wiki/Netherlandshttp://en.wikipedia.org/wiki/Framing_(construction)http://en.wikipedia.org/wiki/Framing_(construction)http://en.wikipedia.org/wiki/Framing_(construction)http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-MacDonald-11http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-MacDonald-11http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-MacDonald-11http://en.wikipedia.org/wiki/File:Lehmverputztes_Strohballenhaus.jpghttp://en.wikipedia.org/wiki/File:Lehmverputztes_Strohballenhaus.jpghttp://en.wikipedia.org/wiki/File:Lehmverputztes_Strohballenhaus.jpghttp://en.wikipedia.org/wiki/File:Lehmverputztes_Strohballenhaus.jpghttp://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-MacDonald-11http://en.wikipedia.org/wiki/Framing_(construction)http://en.wikipedia.org/wiki/Netherlandshttp://en.wikipedia.org/wiki/Swalmenhttp://en.wikipedia.org/wiki/Loamhttp://en.wikipedia.org/wiki/Load-bearinghttp://en.wikipedia.org/wiki/Cementhttp://en.wikipedia.org/wiki/Cementhttp://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Stuccohttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Bamboohttp://en.wikipedia.org/wiki/Foundation_(architecture)http://en.wikipedia.org/wiki/Brickwork#Stretcher_bondhttp://en.wikipedia.org/wiki/Brickwork#Stretcher_bond
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    Straw bale construction

    Straw bales can also be used as part of aSpar and Membrane Structure(SMS) wallsystem in which lightly reinforced 2" - 3" [5 cm - 8 cm]guniteorshotcreteskinsare interconnected with extended "X" shaped light rebar in the head joints of thebales.[13]In this wall system the concrete skins provide structure, seismicreinforcing, and fireproofing, while the bales are used as leave-informworkandinsulation.

    Typically "field-bales", bales created on farms with baling machines have been

    used, but recently higher-density "precompressed" bales (or "straw-blocks") areincreasing the loads that may be supported. Field bales might support around 600pounds 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 tobound modules of other oft-recycled materials, including tire-bales, cardboard,paper, plastic, and used carpeting. The technique has also been extended to bagscontaining "bales" of wood chips orrice hulls.[3][4]

    Straw bales have also been used in very energy efficient high performancebuildings 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 hashoused luminaries such as Nelson Mandela and Tony Blair[15]. In the Swiss Alps,in the little village ofNax Mont-Noble, construction works will start in 2011 forthe first hotel in Europe built entirely with straw bales.[16]

    http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-MacDonald-11http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-MacDonald-11http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-MacDonald-11http://en.wikipedia.org/wiki/Spar_and_Membrane_Structurehttp://en.wikipedia.org/wiki/Spar_and_Membrane_Structurehttp://en.wikipedia.org/wiki/Spar_and_Membrane_Structurehttp://en.wikipedia.org/wiki/Gunitehttp://en.wikipedia.org/wiki/Gunitehttp://en.wikipedia.org/wiki/Gunitehttp://en.wikipedia.org/wiki/Shotcretehttp://en.wikipedia.org/wiki/Shotcretehttp://en.wikipedia.org/wiki/Shotcretehttp://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-12http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-12http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-12http://en.wikipedia.org/wiki/Formworkhttp://en.wikipedia.org/wiki/Formworkhttp://en.wikipedia.org/wiki/Formworkhttp://en.wikipedia.org/wiki/Rice-hull_bagwall_constructionhttp://en.wikipedia.org/wiki/Rice-hull_bagwall_constructionhttp://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-Steen-2http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-Steen-2http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-Steen-2http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-13http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-13http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-14http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-14http://en.wikipedia.org/wiki/Naxhttp://en.wikipedia.org/wiki/Naxhttp://en.wikipedia.org/wiki/Naxhttp://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-15http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-15http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-15http://en.wikipedia.org/wiki/File:Straw_bale_house03.jpghttp://en.wikipedia.org/wiki/File:Straw_bale_house03.jpghttp://en.wikipedia.org/wiki/File:Straw_bale_house03.jpghttp://en.wikipedia.org/wiki/File:Straw_bale_house03.jpghttp://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-15http://en.wikipedia.org/wiki/Naxhttp://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-14http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-13http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-Steen-2http://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-Steen-2http://en.wikipedia.org/wiki/Rice-hull_bagwall_constructionhttp://en.wikipedia.org/wiki/Formworkhttp://en.wikipedia.org/wiki/Straw-bale_construction#cite_note-12http://en.wikipedia.org/wiki/Shotcretehttp://en.wikipedia.org/wiki/Gunitehttp://en.wikipedia.org/wiki/Spar_and_Membrane_Structure
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    There are two main types of strawbale construction: loadbearing and non-loadbearing.

    In loadbearing strawbale construction, which is also known as Nebraska-stylebecause it was originated in the 19th century by pioneers in the Nebraska

    Sandhills, the bales hold the weight. Although more traditional, this type of straw-bale construction is more unusual because it is harder to maintain structuralintegrity. In a poorly constructed loadbearing strawbale house, the straw mightbegin to compress over time, damaging the walls and roof.Non-loadbearing construction is also known as post-and-beam, and is moresimilar to conventional building methods. A frame of wood or other materials isconstructed and the bales are placed in the walls as filler.This is the easier andmore common type of strawbale construction.A thick layer of plaster is used to finish the walls of both types ofstrawbale house.

    Straw: A Renewable ResourceStraw, 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 justwasted in this country alone. Wheat, oats, barley, rice, rye, and flax are alldesirable straws for bale walls. Even though the early bale homes used hay for thebales, hay is not recommended because it is leafy and easily eaten by creaturesgreat and small. Straw, tough and fibrous, lasts far longer. Straw-bale expert MattsMyhrman estimates that straw from the harvest of the United States' major grainscould be used to construct five million, 2,000 square-foot houses every year! Moreconservative figures from the U.S. Department of Agriculture indicate thatAmerica's farmers annually harvest enough straw to build about four million, 2,000square-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 houserequires about 300 standard three-wire bales of straw (costing approximately$1,000). Placed on a foundation, the bales are skewered on rebar pins like giantshiskabobs. After wiring and plumbing, the walls are sealed and finished. Because

    grains are grown in almost every region of the country, straw bales are readilyavailable, with minimal transportation costs. Lumber from trees, in addition tobecoming more scarce and expensive, must be transported over longer distances.

    TYPES OF STRAW BALESStraw bales come in all shapes and sizes, from small two-string bales to largerthree-string bales and massive cubical or round bales. The medium sized

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    rectangular three-string bales are preferred for building construction. Three-stringbales are better structurally, have higher R-value, and are often more compact. Atypical medium-sized, three-wire bale may be 23" X 16" X 42" and may weighfrom 75 to 85 pounds. The smaller two-wire bales, which are easier to handle, areroughly 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 STRAWStraw has been used for centuries by builders who recognized its structuralintegrity. A piece of straw is simply a tube made of cellulose. Tubes are recognizedas one of the strongest structural shapes. Straw was first used to reinforce mudagainst cracking. A lattice of straw criss-crossing a layer of mud produced asurface that remained crack free for decades, or in many cases, centuries. With thelate 19th century invention of the baler, builders were given a convenient new

    building block, the rectangular bundle of straw. Straw-bale building in the UnitedStates has been mostly structural (Nebraska-style) and non-structural. Pliny Fisk IIIof the Center for Maximum Building Potential in Austin, Texas, describes thefollowing five methods of building with straw.

    1. In-fill or non-structural bale - This building system, useful for construction oflarge structures, depends on a pole or post-and-beam building design. Post-and-beam construction employs a skeleton of vertical posts and horizontal beams tosupport the roof. The straw-bale walls have only themselves to support. The balesare 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 buildingstotaling 4,500 square-feet of space using this method.

    2. Structural bale - Automatic straw balers create tight building blocks that arestacked up to one and one-half stories. The "Nebraska-style" buildings originatedon the Great Plains where structural wood was not available. Bales are stuccoed onthe exterior and plastered on the interior to protect them and provide an attractivefinish. 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 theloose straw produces a straw-reinforced clay mud. In the past, this mixture waspacked into a double-sided wood form between the posts and beams of a timber-frame building. Today, a light weight wooden ladder like frame replaces the oldheavy timber frame. European heavy timber structures using this method are stillstanding after more than 200 years. This method has passed the most stringentEuropean fire codes.

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    4. Mortar bale - Structural mortar, made of portland cement and sand, is appliedbetween the straw bales. When dry, its lattice structure remains intact if the strawbales should ever fail. This method, developed in Canada, passes Canadianbuilding codes. Bales are stuccoed on the exterior and plastered on the interior toprotect them and provide an attractive finish. The mortered joints, stucco, andplaster also add to the structural integrity of the wall system.

    5. Pressed straw panels - Straw is compacted under certain temperatures. Theresulting panels are 100 percent straw that can be used to build pre-fabricatedstructures, not only walls, but also roofs and floors.

    FIRE RESISTANCE

    Fire resistanceWe would have liked to do our own test to compare strawbale with brick veneer butwe were not able to get suitable equipment, so we researched tests done by otherpeople.Straw bale buildings are extremely hard to burn. This is because the bales holdenough air for good insulation but because they are compacted tightly they dont holdenough 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, theplaster surface withstood temperatures of about 1,850 F for two hours before anycracks developed. According to the Canada Mortgage and Housing Corporation, "Thestraw-bales/mortar structure wall has proven to be exceptionally resistant to fire. Thestraw bales hold enough air to provide good insulation value, but because they arecompacted firmly, they don't hold enough air to permit combustion."*In 1993 the New Mexico Straw Bale Construction Association commissioned SHBAgra to test strawbale walls for fire resistance. The tests showed that such walls arefire 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 TestingIn 1993, as part of the testing commissioned by the New Mexico-based Straw BaleConstruction Association which eventually led to the inclusion of straw bale in the

    http://foodforest.com.au/bushfireTest.htmhttp://foodforest.com.au/bushfireTest.htmhttp://foodforest.com.au/bushfireTest.htm
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    New Mexico building code, fire testing was undertaken on a straw bale wall panel bySHB Agra, Inc.Transmission of heat through the unreinforced [unplastered] straw bale during its testwas not sufficient to raise the average temperature at the exterior face of this wall to250F above the initial temperature (the governing criteria for ASTM E-119). The

    highest average temperature recorded on the unexposed face of the unreinforced strawwas 52.8F at thirty minutes. Transmission of heat through the wall did not exceed theallowable limit for any single thermocouple. Additionally, there was no penetration offlames or hot gases through the unre-inforced straw bale wall during the thirty minutetest.The burning characteristics of the unreinforced straw bales were observed throughobservation ports during the test. The test panel was also examined after it wasremoved from the combustion chamber. The straw was observed to burn slowly andthe charred material tended to remain in place. The residual charred material appearedto protect the underlying straw from heat and ventilation, thereby delayingcombustion.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 firewas easily extinguished with a small quantity of water.After the unplastered bales passed the 30 minute fire test, plastered bales were testedmore closely simulate real-life burning characteristics on finished walls, with thefollowing results:The highest temperature recorded on the exterior face of the stuccoed straw bales after120 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, howeverat least one thermocouple recorded temperatures exceeding 2,000 F. There was nopenetration of flames or hot gases through the stuccoed straw bale wall.The burning characteristics of the stuccoed straw bales was also observed. Thereaction consisted of initial cracking of the stucco surface as the heat was applied,with little other evidence of distress."Fire retardantsWhere exceptional fire risks exist (eg bushfire areas) some very conservativeAustralian officials insist that since no Australian standard exists proving the fireresistance 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 thewall before the wire netting and plaster layers. Possibly also a fire retardant mixturecould be used. Solomit ceilings which have been used in Australian buildings sincethe 1940s incorporate such a mixture.One mixture is 2 parts by volume Borax to 1 part of granular Boric Acid. Mix withwarm 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

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    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 inmodern houses suggests to us that a strawbale house would be a much safer place tolive. In SA there has been one case of vandalism where a pile of dry hardwood plankswas 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 byitself having burned for some hours, leaving minor damage to the wall. A brick veneerhome would have almost certainly burned to the ground.

    MOISTURE:

    Building with highly variable natural materials could be a daunting prospect, butwe 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 soused to doing this we have few qualms. Humans have been working with woodsince they first picked up a twig or branch possibly hundreds of thousands of yearsago. Despite this very long history of association with the material, it is amazinghow often we can still get timber usage wrong. The latest evidence of this iscurrently occurring in New Zealand with low durability timber rotting undersupposedly impervious claddings. This crisis follows the similar leaky buildingsdisaster that occurred in Canada a few years ago.

    Subsoils are also highly variable naturally occurring materials, and millions ofearth walled buildings have been erected around the world over the last tenthousand years at least. Even so there are not many countries with any systematicstandardisation for unfired earthen materials. New Zealand is, as far as I know, theonly country in the world with a comprehensive suite of earth building standards

    that meet the requirements of a modern performance based building code. In NewZealand, earth has a performance history of at least 150 years and now enjoys thesame status as timber, concrete masonry, and steel as a codified buildingmaterial.

    Cereal crop stems and other plant fibres and leaves have been used in parts ofbuildings for centuries. Generally their use was non-structural and often required

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    frequent replacing. Once machinery made possible the manufacture of bales orblocks out of straw they have seen limited use as the structural component of wallsfor one hundred years or so in some dry climates. Recently the use of suchmaterials has spread into other climatic zones, often taken up by people whoseimagination 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 withthese materials so that they meet the provisions of modern building codes,especially in temperate humid climates with strong wind driven rain such as occursin many parts of New Zealand.

    As Chair of the Standards New Zealand/Standards Australia Joint TechnicalCommittee for Earth Building (BD 083), I rejected an approach made around 1996

    to enlarge our work to write strawbale standards for Australasia, despite the widerange of building methods that utilise both earth and straw. The rejection wasbased on several reasons:

    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 nothave 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 alargely 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 ZealandEarth Building Standards (Ref 1)were published in 1998, and only now hasStandards Australia published an Earth Building Handbook, (Ref 2) whichfalls 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) theresimply is not a long enough history of building in strawbale to enable a Standard tobe written that can ensure adequate performance.

    However, if we were to contemplate such a Standard for a climate such as NewZealands, what would be the starting point for durability performance criteria? Ithink that the short answer is simple.

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

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    The suggestions that follow are derived from the experience dealing with thedesign and construction of earth walled and strawbale buildings in New Zealand,observation of some strawbale failures and successes, together with thoughtsgleaned from colleagues and literature.

    I consider strawbale buildings to be very demanding technically, and must beresponsive to regional and local conditions, especially climatic ones. However,there are significant environmental advantages from using non-toxic naturalmaterials to create highly insulated buildings that will have low energyconsumption over its life (Ref 8).

    These comments do not detail how to achieve desirable outcomes, nor do theyconsider every strawbale construction technique. There will not be an internationalone-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, acknowledgingthat many of these issues require more work to be done before definitiverecommendations can be made.

    A starting point for me is that strawbales are an extremely moisture-sensitive wallmaterial. If they get soaked the tightly bound hollow straw fibres are capable ofabsorbing and holding a great amount of water. Before they can dry out they canremain wet for long enough for fungal decay to start if in a temperate climate with

    high humidity. Plasters leak and water repellent treatments fail. Thereforesuccessful straw bale design relies on keeping the straw bale wall out of the reachof the weather. Then, any moisture that reaches the bale walls is readily dispersedwith 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 throughand 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)

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    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.

    Good hat. Design and build the roof structure so that it can be built first, especially

    given the unpredictable nature of New Zealands 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 bythe provision of eaves or roof overhangs to all strawbale walls.

    Firstly, assess the site for exposure to wind-driven rain as it affects the strawbalewalls.

    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 limitstate of 32, 37, 44, 50, and >50m/s respectively.

    Work out the exposed wall height (the vertical height of the strawbale wall fromthe 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) haveadvocated that in Low wind zones the ratio of roof overhang to exposed wallheight should be 3:4, and for Medium wind zones this should be 1:1. In otherwords, forget eaves - use full verandahs.

    I think that this level of primary weather protection is about right and recognisesthat moisture sensitivity of strawbale walls to external moisture is around one orderof magnitude greater than any other common building materials.

    It should be possible to fine-tune this approach as Driving Rain Indices becomedeveloped (Ref 5).

    For strawbale building we should be aiming for a table or matrix that factors inwind zone, rainfall, driving rain indices, exposed wall heights and roof overhangdistances, but more research is required before this could be completed.

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    The leaky building crisis in New Zealand has recognised the benefit of roofoverhangs for rain deflection (Ref 6) and the NZ Earth Building Standard NZS4299 Amendment #1 (Ref 1) already does this in Table 2.4 that relates siteexposure to a ratio of eaves height to eaves width.

    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 least350 mm above finished ground level or 250mm above a permanently paved striparound the base of the walls that will keep moisture and plants away. Water proofthe top of the footing and do not bridge the damp proof course, taking special carehere with plaster (Ref 3).

    Secondary weather protection

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

    Only buildings that have a wind exposure of Low or Medium are suitable forsingle thickness plastered straw bale wall construction, and then only with the verygenerous overhangs suggested in these guidelines to protect the straw bales walls.The plaster must be durable enough to withstand the weather conditions they willencounter, 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 freelybreathable to allow the easy passage of water vapour, and not trap water behindthem. They also must not be cracked or have holes in them that allow the entry ofwater. 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 beforeplastering is essential. This considerably stiffens up the structure, and helps preventcreep of the plaster substrate, with consequent failure.

    Lime plasters (three coats) appear to be ideal. They adhere well to straw and do notseem to require reinforcing mesh although hair or its modern equivalent ofpolypropylene fibre helps. Lime plasters are durable, are not too brittle, do notcrack readily, are self-healing from small cracks, breathe well, and look good! Anysurface decorative coating must be free breathing.

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    Window/door openings must be very carefully designed with good heads, jambsand sill flashings. These must not leak, either from direct water penetration,soakage through materials, or by capillary action. They must also cast any rain thatmight get past the generous roof overhangs to the outside of the wall surface.Windowsills in particular, especially with rebated windows, can be very trickyareas.

    For sites outside Low or Medium exposure (ie. sites with High, Very High, orSpecific Design wind zones), or with less roof overhang than suggested aboverequire a modified approach. Strawbales, (if used at all), should be placed behind aweather durable and resistant skin that incorporates a pressure equalised,ventilated, vermin proof cavity that drains to the exterior. The precise design ofsuch wall cavities is currently undergoing review in New Zealand as a result of aleaky buildings crisis (Ref 7). The strawbales behind the cladding should be

    encapsulated in a breathing plaster such as lime or earth, and the cladding andcavity must be designed and built to prevent water crossing the cavity to get to thestrawbales.

    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 (ieshelter 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 condensationoccurring on walls.

    Windows, especially if not double-glazed, may get condensation on them and thisneeds 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 baseof the walls safe from any internal flooding eg washing machine leak, or sittingwater if the roof is not built first.

    Passive solar design allows sun into the building, especially in winter, to help keepthe interior warm and dry with adequate heating and ventilation.

    Strawbale walls in wet areas such as bathrooms, laundries and kitchens need tobe carefully thought about to ensure that they will not be subjected to excessiveinternal moisture build up. Splash areas such as showers or behind basins and tapsneed to be waterproofed and given impervious surfaces.

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    Any wet area should incorporate floor drains to prevent flooding saturating thebottom of the wall which will of course be on permanent toe-ups above finishedfloor level with no possibility of moisture bridging upwards past DPCs throughplaster finishes or other means.

    Dynamic movement of water vapour

    To help control water vapour moving into the strawbale walls, encapsulate allstraw to ensure that the walls are not exposed to the atmosphere anywhere, evenbehind cavities or the tops of walls.

    As warm moist air migrates from the interior towards the cold exterior the dewpoint can be reached.

    Clay based plasters help absorb water vapour from the air and dry it out before itcan migrate into the strawbale walls. Earth plasters are only suitable for interiorsurfaces. A high humidity absorbent plaster can be made from perlite and bentoniteclay and this could warrant further research. (Ref 4).

    Cement based plasters are too dense for easy breathability. They are also brittleand tend to crack. My experiments suggest that gypsum plasters, althoughbreathable, provide a more highly heat conductive surface than earth plastersurfaces and might be more prone to interior mould growth.

    Freely breathing surfaces will allow the exit of any water vapour that does get intothe walls preventing it from getting trapped and reaching excessive limits.

    It will help if there are no materials with high heat conducting coefficients or thatcan 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-absorbentinsulating materials resistant to compression. These could form part of the toe upto prevent thermal bridging or possible condensation at this point.

    Do not run water pipes within strawbale walls, not only because of a possible pointfor condensation to occur on, but also in case of leaks.

    Seal around all penetrations in the plaster to maintain the encapsulation of thestraw.

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    Maintenance

    Regularly look over the building for any signs of damage, leaks, or failure,including the roofing, guttering, downpipes, plaster and cladding. Maintain thesurface as necessary, and check that soil or plants have not breached groundclearances. 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 lowenergy consumption buildings can be realised using strawbales.

    TERMITE TREATMENT:

    Non Toxic Termite Control

    DEFINITION

    CONSIDERATIONS

    COMMERCIAL STATUS

    IMPLEMENTATION GUIDELINES

    1. Prevention2. Sand Barriers3. Metal Termite Shields4. Monitoring, Detection and Identification5. Termite Treatment

    DEFINITION:

    Non-toxic termite control is the use of termite prevention and control withoutchemical use. Instead, physical controls are installed during construction such assand barriers or metal termite shields. If termite infestation does occur, least toxicmethods of treatment are used.

    http://nontoxictermite.sustainablesources.com/#Definehttp://nontoxictermite.sustainablesources.com/#Definehttp://nontoxictermite.sustainablesources.com/#Considerhttp://nontoxictermite.sustainablesources.com/#CommStatushttp://nontoxictermite.sustainablesources.com/#CommStatushttp://nontoxictermite.sustainablesources.com/#Implementhttp://nontoxictermite.sustainablesources.com/#Implementhttp://nontoxictermite.sustainablesources.com/#Guidelineshttp://nontoxictermite.sustainablesources.com/#Guidelineshttp://nontoxictermite.sustainablesources.com/#PREVENThttp://nontoxictermite.sustainablesources.com/#PREVENThttp://nontoxictermite.sustainablesources.com/#SANDhttp://nontoxictermite.sustainablesources.com/#SANDhttp://nontoxictermite.sustainablesources.com/#METALhttp://nontoxictermite.sustainablesources.com/#METALhttp://nontoxictermite.sustainablesources.com/#DETECTIONhttp://nontoxictermite.sustainablesources.com/#DETECTIONhttp://nontoxictermite.sustainablesources.com/#TREATMENThttp://nontoxictermite.sustainablesources.com/#TREATMENThttp://nontoxictermite.sustainablesources.com/#TREATMENThttp://nontoxictermite.sustainablesources.com/#DETECTIONhttp://nontoxictermite.sustainablesources.com/#METALhttp://nontoxictermite.sustainablesources.com/#SANDhttp://nontoxictermite.sustainablesources.com/#PREVENThttp://nontoxictermite.sustainablesources.com/#Guidelineshttp://nontoxictermite.sustainablesources.com/#Implementhttp://nontoxictermite.sustainablesources.com/#CommStatushttp://nontoxictermite.sustainablesources.com/#Considerhttp://nontoxictermite.sustainablesources.com/#Define
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    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 TexasAgricultural Extension Service, there is a greater than 70 percent probability thatwooden 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 treatedwood or naturally resistant wood will be required by building codes. Typically,chromated copper arsenate (CCA) pressure-treated wood is used. Two alternativechemical substances have gained popularity as more toxic substances such aschlordane 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 absorbedthrough 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. (SeeWood TreatmentSection.)However, alternatives to wood treatment and chemical treatment can be quiteeffective. Least-toxic strategies must be used in combination to achieve maximumeffectiveness. Few pest control managers expect non-toxic methods to completely

    replace chemical use. However, they offer considerable potential for the reductionof 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 termiteprevention techniques. The USDA Southern Forest Experiment Station in Gulfport,

    Mississippi, and the University of Hawaii are doing research. Successful laboratoryresults have been obtained with the use of properly designed sand barriers. Pestcontrol professionals in California have adapted and tested sand barriers with goodresults. Some studies in California have found some physical barriers to be 15%more effective than chemical treatments.

    http://www.greenbuilder.com/sourcebook/woodtreatment.htmlhttp://www.greenbuilder.com/sourcebook/woodtreatment.htmlhttp://www.greenbuilder.com/sourcebook/woodtreatment.htmlhttp://www.greenbuilder.com/sourcebook/woodtreatment.html
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    SUPPLIERS:

    There are architects and pest management companies in Austin that can provideexpertise and services in non-toxic termite prevention and control. However, notall professionals currently have knowledge or experience with non-toxic termitecontrol.

    COST:

    Initial costs of non-toxic termite prevention may be 25% higher than chemicalcontrols. However, these costs may be offset due to the long term nature ofstructural solutions. In addition, cost offsets can occur if traditional fill material isreplaced 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 non-toxic prevention measures and encouraging financing incentives for their use is agoal of the Green Builder Program.

    PUBLIC ACCEPTANCE:

    For successful termite prevention using non-toxic methods, education andcooperation 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 FamilyDwelling Code) call for protection by chemical soil treatment, pressure-treated

    wood, naturally termite-resistant wood (such as heartwood of redwood and easternred cedar), or physical barriers approved by the building official in areas withsubterranean termites. Approved combinations of methods may be used.

    For decay prevention, any wood (siding, trim, framing) within 6 inches of thefinished grade must be protected. Additionally, wood girders within 12 inches,wood structural floor within 18 inches, and wood sills on masonry slabs within 8

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    inches must also be protected. Decay prevention and termite protection areaddressed jointly with wood treatment and naturally resistant wood. Structuralcontrols for termites such as sand barriers and termite shields will not eliminate theneed for decay prevention in wood within the distances from the ground mentionedabove.

    The Honolulu building code was rewritten in 1991 to include the use of sandbarriers instead of chemical controls. The City of Austin will examine precedentsaccepted 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:

    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 homeswith wood as a construction material, regular inspections should be performed,regardless of treatment and prevention methods. The best method is non-toxicprevention, 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 otherthan wood. However, if wood is used, there are preventative measures available tothe builder other than chemical treatments and treated wood products. A commontree in Austin known to resist termites is the familiar mountain cedar (actually amember of the juniper family). Although not commercially lumbered, natural cedarposts have traditionally been used as foundation piers on old structures, andextensively for fences and furniture. The use of juniper wood has some potentialfor application as a termite and insect resistant wood.Eliminating sources ofchronic moisture in the home is one of the most important factors in managingsubterranean termites, carpenter ants, and some wood boring beetles. Moist soil isnecessary for termites to survive. Termites travel back and forth between soil andfood sources because they must obtain moisture from the soil. In addition, capillary

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    action and water vapor buildup can result in excessive dampness which canactually wick through a concrete slab or masonry foundation to the wood framingabove 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 moisturebuildup in sub-flooring. Foundation wall vents should be placed to provide crossventilation for homes with crawl spaces. If re-grading or remodeling covers vents,additional vents may be needed. Some experts recommend the use of moisturebarriers under slab foundations as well.

    Soil should always be from 6 to 18 inches below any wood member, the greater thedistance, the better. Good siting and drainage design will help to prevent moisturebuildup in and around the structure. All exterior grades should slope away from thestructure to provide drainage. Porches and features such as planter boxes should beconstructed and sealed to prevent moisture and soil contact with the structure.

    Exterior landscaping should not cause moisture build-up around the foundation. Asmall air space should be retained between plant leaves and walls to preventmoisture and mold build-up. Automatic irrigation heads should be properly alignedor shielded to prevent direct spray onto the building.

    Areas subject to moisture build-up, such as bathrooms, should be given specialattention since they are likely to be attack areas. Areas under tubs and drainsleading to the exterior (such as air conditioner drains) should be consideredvulnerable spots.

    All wood-to-soil and wood-to-concrete contacts should be eliminated for fence anddeck posts, rail supports, and trellises etc. Posts should be placed in metal holders(commercially available). Even treated deck piers may not deter termites since theymay 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 becompletely moisture sealed. Exterior siding, especially along the bottom walledges, should be completely moisture sealed on all exposed surfaces.

    All lumber scraps, wood debris and stumps should be removed from the site afterconstruction is complete. Backfill under a foundation should never contain woodscraps, and scrap should never be left in crawlspaces or under foundations. Suchscraps are invitations to termites to eat first the scrap and then move on to the mainstructure.

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    2.0 Sand Barriers

    Sand barriers for subterranean termites are a physical deterrent because thetermites cannot tunnel through it. Sand barriers can be applied in crawl spacesunder pier and beam foundations, under slab foundations, and between thefoundation and concrete porches, terraces, patios and steps. Other possiblelocations include under fence posts, underground electrical cables, water and gaslines, telephone and electrical poles, inside hollow tile cells and against retainingwalls.

    Sixteen grit sand or cinder is placed in a 20-inch band on the soil surface or intrenches next to foundation walls. The sand layer should be 4 inches thick at thefoundation, 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 sandpump, that blows sand under the house. For sand barriers around the outsideperimeter of a foundation, they recommend a sand trench in order to avoiddisturbance of the sand. In addition, a cap made of masonry or other materials maybe recommended to protect the barrier from gardening, animals, etc. Tamping ofsand 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 occurin slab foundations. For sand barriers in conjunction with slab foundations, thesand or cinder must be applied before the foundation is poured. Installing the sandlayer of the appropriate mesh size followed by a layer of coarser gravel for gradingto the desired level has worked well. To cut costs, sand treatments may be installedin particularly vulnerable areas of the slab, such as around pipe penetrations, asopposed to under the entire slab.

    Costs for cinder fill under a slab can often be competitive with the costs ofstandard 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 sizeshould be no larger or smaller than that able to sift through a 16-mesh screen. Sandsmaller than 16-grit can be carried away by termite workers; larger sand cansupport tunnel construction by termites. If the sand to be used has some particles

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    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 forbarriers. Crushed volcanic cinder of the appropriate size is recommended by someexperts.

    2.3 Performance

    Sand barriers can also be used to repair seals that have become broken betweenfoundations and other building elements such as porches. Such settling and

    breaking of cold joint seals can occur due to subsidence and temperatureextremes. In laboratory tests, sand was shown to retain its seal against structural

    members after movement similar to earthquakes. Although earthquakes are not aproblem in our area, soil movement and settling due to expansive soils is often aproblem.

    Use of sand barriers is still experimental, and must be followed with post-installation as well as regular inspections. Sand barriers may cost 25 % more thanconventional chemical treatments, however the physical barrier will provide longterm 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 termitedetection device, forcing them to build tunnels on the outside of the shields whichare easily seen. Metal termite shields also help prevent dampness from wicking toadjoining wood members which can result in rot, thus making the material moreattractive to termites and other pests.

    Metal shields are used in conjunction with concrete or solid masonry walls, and arefabricated 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 tightlyconstructed, 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 tar-like bituminous compound.

    Metal flashing and metal plates can also be used as a barrier between piers andbeams of structures such as decks, which are particularly vulnerable to termiteattack.

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    4.0 Monitoring, Detection and Identification

    The Bio-Integral Resource Center (see Resources, General Assistance)recommends the following steps:

    1. Monitor the building at least once per year.2. Identify the species of termite.3. Correct structural conditions that led to the infestation.4. Apply physical or biological controls.5. Spot treat with chemicals if necessary.6. 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 canbecome difficult if such tubes are hidden inside walls, or termites are entering incracks occurring in concrete slabs or foundations.

    Dogs are being used by some individuals to aid in termite inspection. These dogsare trained to detect termites and other wood damaging insects, and can provideinformation about inaccessible areas of the structure. Their keen sense of smell

    coupled with their ability to wriggle into areas too small for human access canmake 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 leasttoxic 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 forcertification documentation, references, and work experience, or check with theStructural Pest Control Board of Texas. Ask if the company practices integratedpest management techniques, or has an experimental license which may benecessary for some alternative techniques.

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    Non-toxic treatments include use of nematodes (microscopic worms), especiallyfor chemically-sensitive individuals or environmentally-sensitive areas. Nematodesare pumped into the infested area, where they will kill the insects. Boric acid baitblocks can be placed around the structure, where they will attract the pests toconsume termiticides without broad application of chemicals. Drywood termitescan 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 (ifthey have not been used previously), sealing of broken seals or open areas, and re-grading of soil outside the foundation to improve drainage or create a gap betweensoil and wood areas such as siding. In addition, termites can be physically removedby trapping or nest excavation.