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Building and Environment 46 (2011) 156e164

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Building and Environment

journal homepage: www.elsevier .com/locate/bui ldenv

Development of a cost effective probe for the long term monitoringof straw bale buildings

Jim Carfrae a,*, Pieter De Wilde a, John Littlewood b, Steve Goodhewc, Peter Walker d

a School of Architecture, Reynolds Building, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UKbCardiff School of Art & Design, Department of Architectural Studies, University of Wales Institute Cardiff, UKc School of Architecture, Design and the Built Environment, Nottingham Trent University, UKdDepartment of Architecture and Civil Engineering, University of Bath, UK

a r t i c l e i n f o

Article history:Received 17 February 2010Received in revised form12 July 2010Accepted 12 July 2010

Keywords:Straw baleMoistureIsothermMonitoring-probeDwellings

* Corresponding author. Tel.: þ44 1803 862369/þ4E-mail address: jim.carfrae@plymouth.ac.uk (J. Ca

0360-1323/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.buildenv.2010.07.010

a b s t r a c t

This paper reviews current methodologies for measuring the moisture content of straw bale walls inbuildings. It discusses the development of an affordable and accurate moisture probe that has beendesigned to be easily assembled by the builder or owner of a straw bale building from items readilyavailable in the United Kingdom (UK). The probe uses a timber block inserted into the wall, relying uponthe measurable moisture variances of the timber and relating this to the surrounding straw. The probesare designed to be used in pairs of varying length, taking measurements at different depths to give anestimate of the moisture gradient through the wall. In order to properly calibrate this device, a full set ofsorption and desorption isotherms were established for both Oat and Wheat straw and three differenttimber species. The results from an environmental chamber have been compared to readings fromspecimens of the new probe installed in a straw bale house in the south west of the UK. The results werefound to be consistent, to within 2%, with the laboratory findings.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

1.1. Background

There is increasing concern and awareness of environmentalissues such as climate change, depletion of fossil fuels, pollution ofnatural resources, and damage to eco-systems. There are manycontributory factors to these changes, but as far as this paper isconcerned, two statistics stand out: in 2009 27.5% of final energyconsumption in the United Kingdom (UK) came from domesticdwellings [1]; and secondly, 10% of the total energy used in the UKis embodied in construction materials [2]. Current Governmentlegislation and initiatives fromwithin the construction industry arefocused on lowering the energy used during the lifetime of newandmore recently existing buildings. To minimise the carbon impact ofenergy efficient houses it is also necessary to consider theembodied energy and origin of construction materials andcomponents [3]. The increased use of renewable building materials,utilising the non-food use of crops such as hemp, flax and straw, is

4 7880 551922.rfrae).

All rights reserved.

gaining prominence [4]. However, there are concerns regarding thelong term effects of moisture on the durability of these materials ina temperate maritime climate such as the UK [5].

The origins of straw bale construction date from the late nine-teenth century in Nebraska, USA, following the introduction ofmechanical baling machines [6,7]. Over the past 120 years strawbale building has largely remained on the fringes of themainstreamconstruction sector. The first straw bale building in the UKwas builtin 1994 and now they number a few hundred projects of varyingsize. Straw bale, a low cost co-product of agricultural grainproduction, offers many benefits but in particular excellent thermalinsulation and low embodied carbon. Straw bale walls have a lowthermal transmittance, typically 0.13e0.19 W/m2 K for a standardthickness of 450e500 mm [8]. During their growth plants absorbatmospheric carbon dioxide through photosynthesis [9]. Thiscarbon remains stored within the plant fabric until it breaks down,making straw bales carbon negative.

1.2. Objectives

As with all plant based materials, including timber, there areconcerns about the long term durability of straw, especially whenused ina temperatemaritimeclimate suchas found inmostof theUK.

J. Carfrae et al. / Building and Environment 46 (2011) 156e164 157

This paper describes work undertaken as part of an on-goingresearch programme by the partners into the moisture perfor-mance of straw bale construction [10]. The research aims to developand validate an improved timber block moisture probe for theaccurate measurement of the moisture content of the straw balewalls in existing buildings. This new probe is based on an originaldesign from Canada [20].

By calibrating samples of timber against samples of straw in thelaboratory, and testing the improved probe in the walls of a strawbale dwelling, it can be established that the probe, using a piece oftimber embedded in the straw, will reach the same moisturecontent as the surrounding straw.

The resulting probe should:

� Retain the affordability and ease of construction of the originalprobe

� Continue to use an ‘off the shelf’ timber moisture meter� Provide accurate measurements of the moisture content ofstraw bale walls.

This paper summarises development of the probe, experimentsto calibrate the probe and present findings from testing of theprobe in straw bale buildings in the UK.

Fig. 1. Protimeter Balemaster in use in a building context.

1.3. Measuring moisture content in straw bale walls

Research has established a reasonable limit for the safe level ofmoisture content for timber used in construction at 28% [11].

Straw is physiologically very similar to timber [12], and compa-rable limits have been proposed [13]. For builders, the suggestedsensible rule is to keep moisture content of straw bales below20e25% [14].

The importance of accurate measurement is clear, and thefollowing methods have been developed to measure either directlyor indirectly the moisture content within straw bale walls:

1. Directly by oven drying samples;2. Indirectly by measuring the relative humidity within the wall;3. Indirectly by measuring the moisture content of timber

embedded within the straw;4. Directly by measuring the electrical resistance of the straw and

determining the moisture content.

Oven drying material is the most accurate and reliable methodof measuring the moisture content of straw [5]. The specimen ofmoist straw is first weighed, then dried in an oven at 105 �C until nofurther weight loss, and then reweighed [15]. This method is wellsuited to the laboratory, but is not suitable for on-going in situmonitoring as it is very intrusive.

Straw moisture content can be indirectly determined bymeasuring the surrounding RH using hygro-thermal sensors. Therelationship between RH and straw moisture content, for a giventemperature, is known as an isotherm. The isotherm curve isparticularly sensitive at moisture contents above 20e25% (Fig. 2),the region of most interest for decay detection. It is thereforeimportant to ensure sensors are reliable and well calibrated. Indi-vidual RH and temperature sensors can be installed in batches ina straw bale wall, and would typically be connected directly orwirelessly to a data-logging system. A set-up comprising 10e20sensors and data-logging will typically cost around £2000e3000 toinstall, the cost reducing proportionallywith the number of sensors.

Electrical resistance measurement is a well-established tech-nique for determining the moisture content of timber [16]. Theelectrical resistance between two pins inserted into the material

varies with moisture and can be directly calibrated for differenttimber species to give the moisture content [17].

An extension of this method has been developed for the remotemonitoring of building structures by using small pieces of timberinserted into the structure with leads connected back to a resis-tance meter [18].

By placing timber blocks within a straw bale wall it should there-fore be possible to indirectly determine the moisture content of thestrawby takingelectrical resistancemeasurements. This is thebasis ofthe straw bale moisture probe developed originally by the CanadianMortgage and Housing Corporation and later developed for use in UKby Goodhew et al. [19e23]. The method assumes that the embeddedtimber will reach some moisture content as the surrounding straw.Probes can be manufactured for a few pounds only.

Rather than measuring the electrical resistance of timber, it ispossible to directly measure the electrical resistance of the strawand thereby determine its moisture content. Developed for use inthe agricultural industry, one such probe is the Protimeter ‘Bale-master’ [24] shown in Fig. 1. The Balemaster consists of a 600 mmstainless steel probe attached to a handheld meter. The tip of theprobe is separated from the rest of the shaft by a plastic collar and itis between this tip and the shaft that the resistance is measured.

The probe is easily inserted into the straw, although a smallhole is required in the covering plaster or render. However thecost of these purpose built straw bale moisture probes (approx.£300) is around twice that of the equivalent timber moisturemeter. The probe is not designed to be left in situ for continuousmonitoring. Calibration of the Balemaster with oven drying forboth Wheat and Oat straw, carried out as part of this research,confirmed a level of accuracy to within 0.5% for bales of averagedensity (90e120 kg/m3).

2. Moisture behaviour of straw

2.1. Moisture phases

Like other plant based construction materials straw is hygro-scopic. It releases or adsorbs moisture vapour to or from the air thatsurrounds it, responding to changing humidity and temperatureconditions. As the local environmental conditions stabilise thestraw moisture content will tend towards equilibrium for a givenrelative humidity (RH) and temperature. Moisture within the strawexists in different phases. At low levels of RH water vapour

Fig. 2. Stages of moisture storage in porous hygroscopic material (redrawn after JohnStraube [35]).

J. Carfrae et al. / Building and Environment 46 (2011) 156e164158

molecules in the straw ‘cling’ to the pore walls, in a phase calledmolecular adsorption. As the RH increases the water molecules will‘clump’ together and begin to fill the pores and form layers onthe capillaries, starting the phase called capillary condensation. Asthe RH approaches 98% the capillaries fill with water eventuallyreaching capillary saturation, also known as the fibre saturationpoint. This is the maximum moisture content of the straw, afterwhich water condenses out of the air at 100% RH and free waterforms within the straw. These various moisture phases are illus-trated in Fig. 2 below. All moisture contents in this paper areexpressed as percentage of dry mass of straw.

2.2. Isotherm tests

BS EN ISO 12571 [25] allows two alternative methods to estab-lish isotherms of materials. The first method uses saturated salts ina desiccator to provide the different levels of relative humidity. Thismethod has the advantage of allowing more than one sample ofstraw to be tested in different relative humidities at the same time,thus shortening the overall time taken to establish the isotherm.The second method involves the use of an environmental chamber.As set out in the ISO, three samples of straw are first dried ina laboratory oven at 105 �C [15] and weighed at intervals until allthe moisture had been driven off, thereby establishing their drydensity. They are then placed in the chamber and again weighedat intervals until they reach equilibrium at a series of pre-sethumidities. The humidity of the chamber is then incrementallyincreased until a new equilibrium is reached. The process can bereversed and a desorption isotherm plotted. The advantage of usingthis method is that the same specimens can be kept in the chambercontinually, allowing the complete cycle of adsorption anddesorption to be observed, and this is why it was the chosen for thisresearch.

Six sampleswereprepared for the environmental chamber, threeofWheat straw, and three of Oat straw. The ISO specifies aminimummass of 10 g, and that specimens of materials with a dry density ofless than 300 kg/m3 shall have an area of at least 100mm� 100mm.

Fig. 3. Samples of straw in the

The specimens used for the isotherms measured approximately100mm� 200mm� 300mm each and had amass of between 100and 140 g. The prepared samples had a density of around 15 kg/m3

compared to a typical bale density of 90e120 kg/m3, as a lowerdensity will reduce the time taken to reach equilibrium. They wereplaced in lightweight aluminium trays that were used to transportthe samples fromthe laboratoryoven to the environmental chamberand the electronic scales, as shown in Fig. 3.

Environmental Chamber.

Fig. 4. Sample of straw in desiccator at 97.42% RH.

J. Carfrae et al. / Building and Environment 46 (2011) 156e164 159

Due to the size of the specimens it was not possible to set-upa system whereby the samples could be weighed in the chamberwithout beingmoved. Some initial tests were performed to confirmthat the samples were large enough not to be adversely affected bythis relatively short change in their environment during weighing.The frequent opening of the chamber door did effect the environ-ment inside the chamber, but it returned to equilibrium within15 min, and so was considered to have a minimal effect.

In order to establish the isotherm, the sorption process wasstarted at 30% RH and increased in steps of 10% at a time until 90%was reached. After this point the final two steps would be at 95%and 98%, which was the specified maximum RH that the chambercould sustain. Following the stipulation of BS EN ISO 12571, the RHof the chamber was being monitored with two different hygrom-eters, a TES 1365 and a Solamat MPM4100, both of whom had beencalibrated over saturated salt solutions to confirm their accuracy. Ata setting on the chamber of 30% the readings from the twohygrometers and the chamber were within 1% of each other, but asthe RH levels increased discrepancies grew until, at the point wherethe chamber reached its theoretical maximum of 98%, the twohygrometers agreed that the chamber was under reading by 4.8%This gave the chamber a practical maximum of only 93.2%. There-fore, to establish isotherm of the Wheat straw specimens at higherRH, a specimen was placed in a desiccator over a saturated saltsolution of Potassium Sulphate (K2SO4); providing an RH of 97.5% at23 �C, Fig. 4.

During the straw isotherm tests, three specimens each of Pine,European Oak and Ramin, three distinctly different timber species,were also placed in the environmental chamber alongside thestraw, for direct comparison. Pine was chosen because this was thetimber used in the first Canadian probes. European Oak was testedas it was used in the original Goodhew probe. Ramin, a hardwoodfrom south-east Asia was chosen for two reasons: it is a relativelylight and open pored hardwood (attributes that could help makethe timber more responsive to changes in RH); and secondly Raminis widely used in the manufacture of broom handles and dowelsand is therefore widely available in convenient dimensions.

Fig. 5. Sorption isotherms for all six s

2.3. Sorption isotherms for Wheat and Oat straw

Fig. 5 shows the sorption isotherms for three specimens ofWheat and Oat straw and the resulting sorption isotherms up to thehighest levels of RH achieved in the chamber (93.2%). Compared toWheat the average moisture content for Oat straw was very similarthrough the range up to 90% RH with a difference of only 0.3%,falling slightly at 93.2% RH with a lower value of 22.5% (1.9% lowerthan the Wheat).

amples of Wheat and Oat straw.

Fig. 6. Complete sorption and desorption isotherm for Wheat straw.

J. Carfrae et al. / Building and Environment 46 (2011) 156e164160

Fig. 6 shows only the averaged results for Wheat and clearlyillustrates hysteresis [26]. The implications of the hysteresis effectare discussed at more length later in this paper. The completeprocess of sorption and desorption took five months to complete.Added to the isotherms from the chamber is the result from thesample of Wheat straw kept over a saturated salt solution of K2SO4,which achieved amoisture content of 37.6% after nearly fourmonthsin the desiccator.

3. Development of a low cost probe

3.1. History

The original design of the Canadian probe was modified byGoodhew [21] to incorporate a small disc of EuropeanOak (diameter22mmand thickness of 5mm)heldwithin a perforated plastic tube.The arrangement to be inserted into the straw bale wall is shown inFig. 7. It is assumed that as the probe stabilises the air in the perfo-rated tube will be at equilibriumwith the air surrounding the indi-vidual pieces of straw in the wall and that the relative humidity ofthat airwill be adsorbedby the timberdisc togive the samemoisturecontent as the straw. The timber disc moisture content is indirectlymeasured using an electrical resistance meter [27].

A total of 24 probes (12 pairs) were installed into an infill strawbale domestic dwelling in Totnes, Devon, England. The probes wereused in pairs of one 350 mm long and one shorter at 150 mm,inserted into a series of locations in the exterior walls of the house.

Fig. 7. Section through original probe m

Placed about 100 mm apart, the probes thus measuring the mois-ture at two depths through the wall, one at 50 mm from the insideface of the straw, the other 50mm from the outside therefore givingan indication of the moisture gradient across the wall. A Protimeter‘Timbermaster’ was used to measure the timber disc moisturecontents. The probes were used to monitor the house over a periodof sevenmonths fromNovember 2006 through toMay 2007 duringwhich time the house was heated, when required, to a nominal21 �C. Throughout this period the probes indicated straw moisturecontents between 10% on the interior side of the wall and 13.7% onthe exterior face. Based on previous work [28], and compared topublished isotherms for straw [5,28e32], these figures were lowerthan expected. Therefore, the probes were checked and comparedto moisture contents measured using the Protimeter Balemasterinserted alongside each of the probes to the same depth throughthe wall. Typical examples of these momentary measurements,taken at seven different locations through the house, are presentedin Fig. 8. The probes underestimate the straw moisture content,compared against the Balemaster, by between 14% and 24%, thediscrepancy increasing as straw moisture content increased.

Comparison between the calibrated Balemaster and the originalprobe confirms that the probes are consistently under-recordingthe moisture levels in the walls. Assuming that the basic principleof using a piece of timber to mimic the moisture content of thestraw is valid, the inaccuracy of the original probes is likely to becaused by two different factors: flawed design of the probe; and/orinappropriate timber species used for discs. The original probe was

odified from the Canadian design.

Fig. 8. Comparison of the original probes with the Balemaster.

J. Carfrae et al. / Building and Environment 46 (2011) 156e164 161

designed to keep the timber disc physically separate from the straw.Although this remains sound in principle, it is possible that theperforated tube surrounding the timber disc is affecting the relativehumidity of the air next to the disc. Previous research had selectedEuropean Oak for the discs [33].

3.2. Testing of different probe designs

To explore the influence of the perforated tube on accuracy,a series of three different designs of the probe were prepared: twowith different versions of a shroud to keep the timber away fromdirect contact with the straw (but each one removing an element ofseparation between the timber and straw), and a third that allowedthe timber to have direct contact with the straw. The first probe hasa simplified version of the original perforated tube, but madeshorter, and with larger holes, so the timber disc is exposed toa smaller volume of air, and the ratio of closed space to open space

Fig. 9. Prototype timb

(through the wall of the tube) is greater. The second probe still hasa shroud, but it is simply a short extension of the tube, just enoughto keep a physical separation between the timber and straw whilststill allowing a minimal separating air space. The third prototypechanges the timber disc into a bullet shaped projection at the end ofthe tube that will force the timber into direct contact with thestraw. In constructing all the probes importance was placed oninstalling the brass bolts in clear wood, away from knots, splits,resin pockets, visible variations in grain structure, or pockets ofdecay, etc. and parallel to the grain.[34]

The three variations are shown in Fig. 9. There are examples oftimber being placed in a straw wall during the construction phaseto measure the moisture content through direct contact with thestraw [19]. The difference here is that the prototype probe with thebullet tip can be inserted into a wall at any time, and could also beremoved and re-used without any damage beyond the necessaryhole drilled in the interior finish of the wall prior to insertion.

er block probes.

J. Carfrae et al. / Building and Environment 46 (2011) 156e164162

The three prototypes were inserted into a section of the externalstraw balewall of the straw bale house inTotnes. Holes sufficient forthe probes were drilled through the internal render along a hori-zontal line spaced about 100 mm apart. Alongside them a furthertwoholesweredrilled toallow theBalemaster andaTESRHmeter tobe inserted. One of the original probeswas also added as a reference.

3.3. Testing the design prototypes

The three design prototype probes were kept in the stableenvironment of the interior of the house for ten days before beinginstalled in the wall. Measurements with the Balemaster of theinterior of the wall showed that the moisture content of the strawwas 15%. Following insertion the probe moisture contents wererecorded at 24-h intervals. After 20 days the readings of the probeshad stabilised, suggesting they had reached equilibrium with thesurrounding straw. The stabilised moisture content readings of thedifferent probes taken over seven days were as follows:

Original probe. 10.9%First prototype (vented shroud). 13.4%Second prototype (open shroud). 13.0%Third prototype (bullet tip). 14.0%Protimeter Balemaster 15.0%

These tests confirmed that the original probe consistently under-estimated the straw moisture content. The bullet tipped probe waswithin 1% of the Balemaster reading. The other two prototypes arewithin 2%. All probes recorded lower moisture contents than theBalemaster. There are two possible explanations for this. The strawbale isotherms in Fig. 6 show distinct hysteresis during thedesorptionphase [26]. If the straw in thewall is in aprocess of dryingthen it would indicate a higher moisture content than a probe thatwas previously dry even when they have both reached equilibriumat the sameRH. Theprobewill thereforegive adifferent reading thanthe surrounding straw, unless it has also been subjected to exactly

Fig. 10. Section of averaged sorption isotherms f

the same moisture history. Taking account of this hysteresis affecthas been a factor in the detailed calibration of the timber blockprobes. The other reason for the lower readings could be explainedby comparing the isotherms for the three different timber species. Itis known that due to their similar physical make up, [12] straw andtimber exhibit similar moisture behaviour, but this needs to beconfirmed in the laboratory by comparing the isotherms.

3.4. Timber isotherms

Fig. 10 compares the three timber species withWheat straw. Theresults of the timber isotherms were similar to the straw isothermsin Fig. 5 in that the results for all three samples were close to eachother, soonly the averaged results of each of the three samples ofeach of the species are shown. Covering the section of the sorptioncurves from 45% upward, it omits desorption to make it easier tocompare the different traces.

None of the species has exactly the same development as thestraw. However, as this work is most interested in the behaviour ofthe straw at RH values higher than 80%, it can be seen that Ramin isthe closest fit to the Wheat. The Pine and Ramin samples showedsimilar reaction time to changes in the RH of the chamber to thestraw with Oak lagging slightly behind.

As a result of the above findings Ramin was chosen for the newprobe design to be tested in the walls of the Totnes house. Forty-eight pairs of prototype probes were built in short (100 mm) andlong (350 mm) form like the origin also as to measure the moistureat the inside and outside of the straw in a wall. Each probe wascalibrated at 80% RH in the environmental chamber to conform toa tolerance of plus or minus 1.5%. The results were interesting inthat all but a small number conformed, but the examples that didn’tall give a lower moisture content of around 5%. All the probesexhibiting this anomaly were traced to a different batch of thetimber used and were discarded. Future probe manufacture willhave to be aware of potential variations in the timber used.

or three species of timber and Wheat straw.

Fig. 11. New probe with Timbermaster meter.

J. Carfrae et al. / Building and Environment 46 (2011) 156e164 163

3.5. In situ testing of new probes

Following the completion of the laboratory isotherms, inJanuary 2008 the new probes were installed in an exterior wall ofthe Totnes house. The first two examples of the new probes wereconstructed with a bullet shaped tip formed from Ramin, fitted touPVC tubes made up to a length of 350 mm. Fig. 11.

When inserted from the inside into the wall, the length of theuPVC tube placed the timber in the outside 50 mm of the strawwall. The probes were inserted at a height of 50 mm from thebottom of the wall, which was known to be the area with thehighest RH following monitoring with a TES 1365 temperature andRH meter. Prior to installation, one of the probes was moisteneduntil it registered a moisture content of 25.6%, and the other wasdried to a moisture content of 10.2%. This was carried out to exploreif the probeswould show evidence of the hysteresis effect over timein the environment of the straw bale wall.

Fig. 12 shows the readings from the two probes compared to theBalemaster and the RH meter during the three months from

Fig. 12. Two new probes com

January toMarch 2008. The readings have been corrected accordingto the instructions supplied with the Timbermaster meter usedwhich calls for a correction factor of plus 0.1% for every 1� below20 �C, and minus 0.1� for every 1� above. This broadly accords withthe Nordtest Method [18].

The RH at this location varied between 88% and 90.5%. Referringto the isotherms this would give an expected moisture content ofbetween 20% and 22% on the desorption curve, and between 18%and 20% on the sorption curve. Looking at the readings from thetwo probes in the wall, the previously wetted one is readingbetween 20% and 20.5%, and previously dried one is readingbetween 18.8% and 19.8% (taken from the beginning of March,allowing a period of a month for them to stabilise). The readingsfrom the probes are almost exactly within the expected range, butdo not follow the variations in RH as closely as expected.

The long term monitoring of the Totnes house had revealedan episode where the moisture levels in this wall had reached26% (measured with the Balemaster) six months before thisexperiment, so it was hoped that the probe that had beenpreviously wetted to the same moisture content would givesimilar readings during the period covered in Fig. 12. Thepreviously wetted probe and the Balemaster are showing almostexactly the same readings, with the dry probe following thesame variations, but remaining at least 1% lower, which confirmsboth the accuracy of the new probes in this situation, and thathysteresis appears to be continuing to affect the probes. Resultscoming in from sets of probes in different case study buildingstend to confirm these results.

4. Summary, conclusions and further work

This paper summarises work from on-going study on themoisture monitoring of straw bale walls. Results of laboratoryisotherms demonstrating the relationship between cereal strawand different timber species, coupled with the in situ testing in thestraw bale walls of the Totnes house, has enabled the developmentof an improved moisture probe that: is reliable and easy to produce

pared to the Balemaster.

J. Carfrae et al. / Building and Environment 46 (2011) 156e164164

at a unit cost of less than £20; can be used with an ‘off the shelf’timber moisture meter.

The improved probe has been calibrated against a new set oflaboratory isotherms, and the timber chosen, Ramin, displayedamoisture contentwithin1.5%of theWheat straw in the critical regionof 80e94%.When installed in the straw balewall and compared to thecalibrated Balemaster, the new probe gave results to within 1% of theBalemaster. The resulting probe can be left in situ for the continuousmonitoring of the moisture content of straw bale walls.

Although more sophisticated devices such as relative humidityand temperature probes can be used, these timber block probes canbe produced in large numbers, and in the latest phase of thisresearch, 48 sets of the long and short probes have been installed ina range of straw bale buildings that are being used for a variety ofdifferent forms of habitation. The results of one-year’s monitoringof these eight case study buildings will be complete by the end ofFebruary 2010.

Acknowledgements

This research gratefully acknowledges support from GreatWestern Research, The Ecology Building Society and The NationalNon-Food Crop Centre.

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