Humidity in straw bale walls - thesis, ♦ BARDZO WAZNA INFORMACJA, Domy ze słomy budownictwo ekologiczne, ...
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UniversityofEastLondonSchoolofComputingandTechnology
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Humidityinstrawbalewallsandits
e®ectonthedecompositionofstraw
JakubWihan
1
July2007
1
I'dliketothankMikeThompsonforrunningthecourse.Mythanksaredueto
Sharonforediting,sel°esssupportandlove,toAdamandZabelleaswellastomy
fatherJosef,motherMaria,brotherLukasandhiswifeMarketa.WithoutthemI
wouldn'thavebeenabletostartor¯nishthecourse.Iwasveryfortunatetohave
BobbyGilbertandSo¯ePelsmakersassupervisors;thankyouBobbyforseeingthe
potentialinthisthesis. I'dliketoexpressmygratitudetoMartinandMarianne
Oehlmann,HerwigVanSoomandhisfamily,BeeRowan,BarbaraJones,alltheAm-
bassadors,TomRijven,SimonAyres,TomasFicker,TimPad¯eld,DanielZirkelbach
forthefreeuseofWUFI,allthewonderfulstrawbalebuildingprofessionalsfrom
GSBNdiscussionforumandKay.Thisworkisthemanifestationofalifeforce,rep-
resentingitselfasaneverlovingStrawBaleGoddess.
Preface
OnedayinOctober2005,MartinOehlmannwasstandingbythewindowin-
sidehisandhiswife'sun¯nishedstrawbalehouseontheoceanfrontinBrittany,
France.Therewasastormoutside.Hewasobservingthemonstrouswavesin
thedistancewithachildlikecuriosity,whiletheraincomingovertheraging
oceanwasviolentlyhittingthewindowpanesandexteriorlimeplaster.
"Doyouthinkthelimeplasterwillwithstandthis?"
"Well,wewillsee.Ihopeso.Ithinkso.Thisisthebesttest.I
meanalltheoverhangscoulddoanythinginthissortofrain.Yes,
butI'mquitecon¯dentIwillputonelimewashonandthiswill
continueforfewyears.Sothiswillbeperfect..."Martinsaid.
Severalweeksafterthisconversation,onDecember1st,2005,itstormed
again,thistimewithevengreaterintensity.Thestormlastedfor48hours
nonstop.Twodaysofraindrivenbystrongcoastalwindscausedthesaturation
ofstrawwithinthelimeplasteredwesternwall,somuchthatwetspotsappeared
ontheinsideofthebuilding.
Willthestrawhaveachancetodrybeforeitdecomposes?Whatcouldhave
beendoneinordertopreventsuchadisaster?Howto¯xthedamage?These
questionsandtheanswerstothemsummarisethepurposeofthisthesis.
²
Thisthesisexplorestheuseofstrawasabuildingmaterial. Incurrent
practice,strawiscompressedintobales,whicharethenusedinthewalls,ei-
therasloadbearingbuildingblocksorassuperinsulation
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usedasin¯llinthe
constructionframe.
Ashifttowardenvironmentallyconsciousbuildingcanbeobservedinmany
countriesandcommunities,noticeablytheUK,DenmarkandGermany.The
productionofwallsfromlocalstrawbales,plasteredwithlocalearth,hasan
incrediblylowenergydemand,makingthisbuildingmethodextremelyprogres-
sive.Withgrowingenvironmentalawareness,contemporarybuilderswillsoon
beobligedtousesustainablemethodsduringtheconstructionofnewhouses.
Withoutadoubt,strawbalesrepresentoneofthemostappropriatewaysof
buildinginourendangeredworld.Theirusenotonlylowerstheenergydemand
forproductionofnewmaterials,butforheatingorcoolingbuildingsaswelldue
totheirexcellentthermalinsulatingproperties.
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Thermalconductivityofstrawmeasuredthroughstrawbalewithdensity90kg
¢
m
¡
2
is:
¸
=0.6W
¢
m
¡
1
¢
K
¡
1
(Andersen,2003).Strawbaleconstructioniscompatiblewithsuperin-
sulation,duetothethicknessofthebales(ordinarilyabout360mmforstrawbaleslaidon
edgeandabout460mmforstrawbaleslaid°at.)
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Whataretheweaknessesofstrawbaleconstruction?
The¯rstdoubtsthatgenerallycometomindinconnectionwithstrawbale
wallsarealwaysrelatedto¯reandrodents.Whiletheseworriescaneasilybe
dispelledbyapplicationofgoodplasterontostraw(Jones,2003),thequestion
ofthevulnerabilityofstrawtomoistureismoreserious.Thisthesisfocuseson
clarifyingtheproblemofmoistureinstrawbalewalls.Itexplainstheboundaries
withinwhichstrawandhumidityinthewallscancoexist.Itinvestigatesthe
questionofhowtostaywithintheseboundaries,sothatstrawbalebuildings
canbecomemoreinnovative,moreprogressiveandbetteradaptedtomodern
climates.
Instrawbalebuildingliterature,theauthorsusuallylimittheuneasytopic
ofmoistureinstrawbalewallstoseveralrulesofthumbexplainingthefunda-
mentalsofmoisturedamageprevention.Thereisverylittleliteratureavailable
thatmanagestoprovideacomplexpictureofmoisturebehaviourinstrawbale
wallsdirectlyconnectedtoprinciplesofstrawdecay.Thereiseitherliterature
explainingthedecayofstraw(e.g.Summersetal.,2003),orliteraturedescrib-
ingtheprinciplesofmoisturebehaviourinstrawbalewalls(e.g.Straube,2005).
Duetogrowinginterestinthistopic,thereisalsoanumberofcasestudieson
moisturemonitoringinexistingstrawbalebuildings(e.g.Fugler,1997).
Thisthesiso®ersaholisticapproach.
²
Itexploresthephysicsofmoistureinwallsinrelationtothedegradation
oforganicmattersuchasstraw.
²
Itconsiderspracticalexperiencethroughcasestudiesofstrawbalehouses.
²
Itcomparessimpledesigncalculationsforthepredictionofmoistureriskin
buildingenvelopes(asareoftenusedasaguidelinebycontemporarycivil
engineersandarchitects)withcomputersimulation,developedinorderto
studymoisturetransferinwallsingreatcomplexity.
²
Itlooksattherelevanceofusingthosecomputationalmethodstopredict
moistureperformanceinsimplestrawbalewallassemblies.
²
Itusescomputersimulationtouncoverthebasicprinciplesofmoisture
transferthroughstrawbalesplasteredwithdi®erentmaterials.
Theconclusionsarecomparedtoknowledgefromexistingsituationsfrom27
professionalstrawbalebuildersinordertogiveacomprehensiveguidelinefor
futurestrawbaleconstructionwork.
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Contents
1Introduction 14
1.1Warming............................... 14
1.2Buildingsector............................ 16
1.3Constructionmaterials........................ 16
1.4Strawbalehouses........................... 18
1.5ThesisOverview........................... 18
2Decompositionofstrawinawall 21
2.1Microorganismsinstrawbales.................... 22
2.2Strawphysiology........................... 24
2.2.1Cellularcomposition..................... 25
2.2.2Lignin............................. 26
2.2.3Silica............................. 27
2.2.4Nutrients........................... 28
2.3Environmentinstrawbalewalls .................. 30
2.3.1Fungicides........................... 30
2.3.2Oxygen............................ 32
2.3.3Moisture,temperatureandexposuretime......... 33
2.4SummaryofChapter2........................ 36
3Relativehumidityasacriticalfactordeterminingthecondition
ofstraw 38
3.1Kinetic(thermal)andelectricalenergy............... 38
3.2Watermolecule............................ 39
3.3Watervapourpressure........................ 39
3.4Saturationwatervapourpressure.................. 40
3.5Moisturecontent........................... 41
3.6Relativehumidity........................... 43
3.7Relativehumidityversusmoisturecontentofhygroscopicmaterials45
3.8Relativehumidityversuswateravailabilitytomicroorganisms.. 49
3.8.1Microorganismsandliquidwater.............. 50
3.8.2Microorganismsandwatervapour............. 51
3.9Relativehumidityversusmoisturecontentofstrawinanactual
wall .................................. 52
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