Construction and Building Materials 23 (2009) 3189–3195

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Construction and Building Materials

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Thermophysical characterization of a laminated solid-wood pine wall

Saed Raji a, Yves Jannot b,*, Philippe Lagière a, Jean Rodolphe Puiggali a

a TREFLE, Université de Bordeaux, CNRS, Esp. Des Arts et Métiers, 33405 Talence, Franceb LEMTA, Nancy-Université, CNRS, 2, avenue de la Forêt de Haye, 54504 Vandoeuvre, France

a r t i c l e i n f o

Article history:Received 15 April 2009Received in revised form 3 June 2009Accepted 18 June 2009Available online 17 July 2009

Keywords:Laminated woodPineConductivityDiffusivitySorptionDiffusion coefficientPermeability

0950-0618/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2009.06.015

* Corresponding author. Tel.: +33 383595627; fax:E-mail address: yves.jannot@ensem.inpl-nancy.fr (

a b s t r a c t

The experimental results obtained by the thermophysical characterization of a wall made of stacked lam-inated solid-wood planks are reported in this article. The interface between two logs is filled with a feltpacking that is compressed under the weight of the upper plank. The characteristics which affect heat, airand water vapour transfers through the wall have been determined, i.e. the sorption isotherm, density,thermal conductivity and diffusivity, water vapour diffusion coefficient, and air permeability of the wall.The results achieved demonstrate the influence of the presence of the laminating adhesive on watervapour and air diffusion, and the influence of the presence of the felt packing on air permeability. Theresult is that the hygrothermal behaviour of the wall studied cannot be described properly by simplytaking into account the properties of the solid wood, and it is thus necessary to determine the globalproperties of the composite wall.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

The ever-increasing consumption of fossil energies and miner-als has led to a strong environmental awareness of industrializedcountries towards both the reduction of energy consumption (inparticular to curb the greenhouse effect) and use of renewable re-sources such as wood [1]). In this regard, the development of woodconstruction represents a major challenge. As a renewable con-struction material, wood requires little energy to be processed,and the wood house thus arises as an interesting alternative asfar as energy consumption and thermal comfort are concerned [2].

The present Log houses in solid-wood construction is due to therecent evolution of traditional techniques. These techniques havebeen greatly improved in terms of energy efficiency, but the energyefficiency and legality of wood houses remain ambiguous. Since2000, the French thermal regulations for new buildings (RT2000)require a minimum wall heat resistance Rwall = 1.91 �C m2 W�1.To achieve this value with a solid-pinewood wall, a wall thicknessof more than 23.5 cm would be required, which is hardly conceiv-able from a technical-economic standpoint. The conclusion will bethe same with Vertically Laminated Log since it will be shown thatthe thermal conductivity is not modified by the adhesive seal. Itshould be noted that this criterion – which characterizes the stea-dy-state energy efficiency – is suitable for assessing light walls

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+33 383595551.Y. Jannot).

(low damping and small phase shift between the various flows),but may prove absolutely unsuitable for assessing the performanceof heavy walls such as solid-wood walls.

The presently studied logs are Vertically Laminated Log (VLL)width of 134 mm and height of 175 mm. The wood used is theScotch pine (Pinus sylvestris L) imported from Finland. The inter-log felt packing, with width of 90 mm and thickness of 8 mm, aremade of polypropylene fibres. The profile of the wall is shown inFig. 1.

The various flows through such a wall are:

– A heat flow induced by the difference Text � Tint; it is gov-erned by the thermal conductivity k, thermal diffusivity a,specific heat c, density q, and thickness e of the wall.

– A moist air flow induced by the difference Pext � Pint; it isgoverned by the permeability k and thickness e of the wall.

– A (diffusive) water vapour flow induced by the differencePvext � Pvint; it is governed by the mass diffusivity DH2O,material–water equilibrium curve (sorption isotherm), andthickness e of the wall.

These three flows follow two parallel paths through the wall, asfar as unidirectional transfers are considered (Fig. 2).

To determine these three flows (heat, air, and water vapour),the parameters (k, a, e, k, q, DH2O, sorption isotherm) of each branch(wood–adhesive–wood and felt packing) need to be known.Various studies have been conducted to characterize the Scotchpinewood in terms of mechanical, hygrometric, thermal or

Nomenclature

a thermal diffusivity (m2 s�1)d diameter of sample (m)DH2O mass diffusivity (m2 s�1)e thickness of the wall (m)E thermal effusivity (J m�2 K�1 s�1/2)RH relative humidity (%)k air permeability (m2)m mass of sample (kg)P pression (Pa)Pv pression of water vapour (Pa)Q air flow (m s�1)R heat resistance (m2 K W�1)Sm specific surface (m2 g�1)T temperature (�C)V volume (m3)Xeq equilibrium water content (kgwater kg�1

dm)

Xm transition water content at monolayer saturation(kgwater kg�1

dm)Xf average equilibrium water content (kgwater kg�1

dm)c specific heat (J kg�1 K�1)k thermal conductivity (W m�1 K�1)q density (kg m�3)

Subscriptsext exteriorint interior|| parallel to the fibres? perpendicular to the fibreswater waterdm dry mattermoist moist matter

Fig. 1. Profile of the wall.

Fig. 2. Schematisation of the two different paths for the three flows crossing thewall.

3190 S. Raji et al. / Construction and Building Materials 23 (2009) 3189–3195

aerodynamic performance, but no results have been published yeton the properties of a composite wall, in particular on the influenceof a lamination and a felt packing.

Thus, physical measurements have been made to determine thevalues of these parameters, first for the various constituents sepa-rately, and then for the whole wall. The values of these parametersare necessary inputs for tools simulating the dynamic behaviour ofthe wall, such as the tools proposed by Hameury [3] or Battagliaet al. [4], to evaluate the energy efficiency of the wall in a muchmore realistic way than by simply considering the value of its heatresistance. The final stage will be the dynamic simulation of indoortemperature and relative humidity to optimise energy consump-tion and thermal comfort.

2. Materials and methods

2.1. Sorption isotherm

The static method based on saturated saline solutions as described by Talla et al.[5] and Bilali et al. [6] was applied to determine the sorption isotherms. Table 1 liststhe 10 solutions used and the air relative humidity values imposed by each solutionat 20 �C, 30 �C, 40 �C, 50 �C, and 60 �C.

The wood samples were placed in atmospheres under RH salt control, andweighed every 48 h until the equilibrium water content Xeq was reached. Whenthe ten masses had become stable, the experiment was stopped, and the sampleswere weighed. Baking the samples at 102 �C for 48 h gave their dry masses mdm.

The GAB model was used to model the sorption isotherms. This model is advan-tageous in that it satisfactorily describes the sorption isotherms at RH values below90% [7]. This model can be expressed as:

Xeq ¼XmCKRH

ð1� KRHÞð1þ CKRH� KRHÞ ð1Þ

where Xeq is the equilibrium water content ðkgwater kg�1dmÞ.

Xm, C and K are constants linked to the product’s characteristics and totemperature.

RH is the relative humidity of the surrounding air.The three constants Xm, C and K are governed both by the product’s character-

istics and by temperature. They are determined by minimising the sum of the qua-dratic differences between the experimental and theoretical curves.

After determining the saturation water content Xm of the monolayer, the surfacearea of the monolayer can be calculated, based on the assumption that it is coveredwith molecules of water. In the case of water, the surface area can be calculatedusing the following equation [5]:

Sm ¼ 3516Xm ð2Þ

where Sm is the specific surface area (m2 g�1) and Xm is the transition water contentat monolayer saturation ðkgwater kg�1

dmÞ.

Table 1Equilibrium water content of pine wood obtained with ten saturated salt solutions at five values of working temperature.

Salt T = 20 �C T = 30 �C T = 40 �C T = 50 �C T = 60 �C

RH Xeq RH Xeq RH Xeq RH Xeq RH Xeq

LiBr 6.60 0.0307 6.20 0.0263 6.20 0.0263 5.50 0.0168 5.30 0.0159LiCl 11.30 0.0410 11.30 0.0389 11.30 0.0389 11.10 0.0283 11.00 0.0258KCH3CO 23.10 0.0604 21.60 0.0560 21.60 0.0560 19.00 0.0410 18.00 0.0366MgCl2 33.10 0.0813 32.40 0.0759 32.40 0.0759 30.50 0.0581 29.30 0.0511K2CO3 43.20 0.0964 43.20 0.0906 43.20 0.0906 45.60 0.0720 45.00 0.0605NaBr 59.10 0.114 56.00 0.107 56.00 0.107 50.90 0.0772 49.70 0.0686CuCl2 68.40 0.140 68.60 0.137 68.60 0.137 65.50 0.1109 63.30 0.0983NaCl 75.50 0.154 75.10 0.152 75.10 0.152 74.40 0.1314 74.50 0.118KCl 85.10 0.174 83.60 0.173 83.60 0.173 81.20 0.1465 80.30 0.130K2SO4 97.60 0.270 97.00 0.264 97.00 0.264 95.80 0.2423 95.70 0.0229

Fig. 3. Hot strip device.

Fig. 4. Hot plate device.

S. Raji et al. / Construction and Building Materials 23 (2009) 3189–3195 3191

2.2. Density

The object of the present study is to establish a relationship between the den-sity and water content of the pine. We have checked that the law of volume addi-tivity set out by Desmorieux and Moyne [8] provides a sufficiently accuraterepresentation of this density. This law is based on the following two assumptions:

– The product has a strong structure with a specific density qdm and a volumeVdm; the pore volume Vwater is filled with water with a density qwater.

– The variation in volume corresponding to a variation in mass equals the vol-ume of evaporated water.

Considering these assumptions and referring to the mass of the product by m, tothe mass of water by mwater, and to the mass of solids in the product by mdm, thefollowing equations can be written:

m ¼ mwater þmdm; V ¼ Vwater þ Vdm ð3Þ

and also:

q ¼ mV

; X ¼ mwater

mdmð4Þ

where X is the water content in the product ðkgwater kg�1dmÞ

The following equations can thus be written:

qqdm

¼ qwaterð1þ XÞqwater þ Xqdm

ð5Þ

and

VVdm

¼ 1þ qdm

qwaterX ð6Þ

The mercury volume measurement method described by Talla et al. [9] was used toassess both the moist density qmoist and dry density qdry at 20 �C. Twenty pine sam-ples of 2 � 1 � 0.5 cm3 were placed in atmospheres under RH saline control, as in thesorption study, to have their water contents controlled. The air relative humidityvaried between 6.6% and 97.6%, and the pine water content varied between 0.031and 0:27 kgwater kg�1

dm.For each sample, the moist mass mmoist and moist volume Vmoist were measured

to give the moist density qmoist.The dry density qdm of each sample was calculated.

2.3. Thermal conductivity and effusivity

The thermal properties of the pine were assessed in the direction of the fibresand in the direction perpendicular to the fibres, on samples (10 samples in eachdirection) with water contents between 0.037 and 0:256 kgwater kg�1

dm.The thermal effusivity E\ and conductivity k\ in the direction perpendicular to

the fibres were measured using the hot strip method with core temperature mea-surements [10]. This study was carried out using a Minco HK913P flat resistor witha resistance of 40.5 X and a heating surface area of 3.3 � 1.2 cm. A T-type thermo-couple made of 0.02 mm wires was arranged to one side of the resistor (see Fig. 3). Aflow step function was applied to the resistor arranged between two wood samples,and the thermocouple temperature was recorded for 120 s with a time step of 0.1 sand a resolution of 0.1 �C. Each measurement was made in triplicate. The thermaleffusivity E\ was assessed between 0 and 20 s by minimising the quadratic differ-ence between the experimental curve and the curve calculated using a 1D hot platemodel. The thermal conductivity k\ was assessed between 20 and 120 s by mini-mising the quadratic difference between the experimental curve and the curve cal-culated using a 2D model.

The thermal effusivity E|| in the direction parallel to the fibres was assessedusing the hot plate method [11]. A Minco HK913P flat resistor with a resistanceof 156.2 X and a heating surface area of 4.0 � 4.0 cm was used (see Fig. 4). A flowstep function was applied to the resistor arranged between two wood samples,and the thermocouple temperature was recorded for 30 s, with a time step of0.1 s and a resolution of 0.1 �C. The thermal effusivity E|| was assessed between 0and 30 s by minimising the quadratic difference between the experimental curveand the curve calculated using a 1D hot plate-type model.

The values of thermal conductivity in the direction of the fibres k|| were calcu-lated using the following equation:

kjj ¼ k?EjjE?

� �ð7Þ

where E? ¼ffiffiffiffiffiffiffiffiffiffiffik?qc

pand Ejj ¼

ffiffiffiffiffiffiffiffiffiffikjjqc

p.

2.4. Diffusion coefficient

The static gravimetric method was applied [12]. Three couples of saline solu-tions were selected and used for each (solid and laminated) wood grade. The fol-lowing couples were formed: (MgCl2; K2SO4), (NaBr; K2SO4), (NaCl; K2SO4); seeTable 1 for the relative humidity values imposed by each solution. For a given cou-ple, the first solution was prepared in a small cylindrical vessel, and the secondsolution in a larger diameter cylindrical vessel.

Six wood samples were prepared as cylinders, three of which were solid woodsamples, and the remaining ones laminated wood samples. The samples haddiameters of 55 mm and thickness of 25 mm approximately. The samples were

3192 S. Raji et al. / Construction and Building Materials 23 (2009) 3189–3195

measured, weighed and secured with leakproof adhesive in the small vessels. Then,the (Small vessel + Saturated Saline solution + Sample) sets were weighed and putinto larger diameter vessels containing the K2SO4 saturated solution. These vesselswere baked at a controlled temperature of 30 �C (Fig. 5).

The masses of the small vessels were recorded over time until the mass varia-tion became constant. Eventually, the samples were cut out in the horizontal direc-tion into thin slices (about 50 mm) using a microtome. The slices were weighed,dried at 100 �C for 48 h, and weighed again. The water content of each slice wascalculated.

The diffusion coefficient DH2O could be deduced from Fick’s law, which specifiesthat the mass flow per surface unit is proportional to the concentration gradient. Byassuming that the coefficient DH2O is not governed by the water content, it can beexpressed as [9]:

Fig. 5. Schematic view of experimental device for mass diffusion coefficientmeasurement.

P0

P2(t)

Differential manometer

Higher room

Lower room

P1 = 2 bars

Tight joints Tight adhesive

Metallic plates

Fig. 6. Schematic view of the permeameter used for permeability measurement.

Wood Tight side A

Solid wood (samples 1 to 4)

Wood with adh(samples 5

Fig. 7. Schematic view of the samples us

DH2O ¼1þ Xf

X1 � X2

1mdry

dmdt

� �4V

pd2

� �2

ð8Þ

where DH2O is the diffusion coefficient (m2 s�1), dm/dt is mass flow per unit time(kg m2 s�1), V is volume of the sample (m3), d is diameter of the sample (m), Xf isaverage equilibrium water content ðkgwater kg�1

dmÞ, X1, X2 are water contents at the ex-change surfaces ðkgwater kg�1

dmÞ, mdm is dry mass of the sample (kg).

2.5. Permeability

The air permeability of a porous material characterizes the capacitance of thismaterial to let such a fluid permeate under a total pressure gradient [13]. The airpermeability of a wall is a major parameter in the assessment of transfers betweenthe interior and the exterior of a building; some wood species have already beenmeasured [14].

Permeability was measured using the device shown in Fig. 6. The test samplewas a wood disc with a varying thickness e and a diameter D2 = 170 mm. The sidesurfaces and the two surfaces between diameters D1 = 150 mm and D2 = 170 mmwere sealed with adhesive. The top surface received a pressure P1 = 2 bars. Theair flow induced through the sample by the pressure differential caused an increasein pressure P2 in the lower chamber (which is isothermal and has a constant volumeV) below the sample lower face. Under steady-state conditions, the curve represent-ing pressure against time is a straight line, with a slope b proportional to the airflow rate, as long as gas temperatures are identical in both branches of the pressuregauge. To ensure this isothermal assumption, the low-pressure branch of the pres-sure gauge was connected to a volume drilled in the lower metal plate. Pressurerecording was stopped in the lower chamber when the pressure increase reached10 mbar; it could thus be assumed that the pressure differential between both faceswas constant. The air flow rate through the sample was calculated based on the fol-lowing relationship:

Q ¼ bVP2

ð9Þ

where V is the (constant and isothermal) volume of the lower chamber.Then, the permeability was calculated using the following equation:

k ¼ Q

pD21

2lP1

ðP21 � P2

2Þð10Þ

where Q is the output volume flow rate under pressure (m3 s�1) and l is the dynamicviscosity of the fluid (Pa s).

The time step of P2 recording was 1 s with an accuracy of 0.025 mbar.Seven samples shown in the Fig. 7 were tested using this device: three solid

wood samples with thickness of 20, 28, 42, and 46 mm, three laminated sampleswith thickness of 19, 32, and 120 mm, and one 13-cm thick laminated sample witha felt packing. Each measurement was repeated five times.

3. Results and discussion

3.1. Sorption Isotherm

The sorption isotherm is the curve showing how the productequilibrium water content Xeq changes with the relative humidityRH (%) of the air surrounding the product. The sorption isothermsexperimentally obtained for the pine at 20 �C, 30 �C, 40 �C, 50 �C,and 60 �C are shown in Fig. 8.

Table 2 gives the estimated values of the three constants Xm, C,and K of the GAB model determined by minimising the sum of the

dhesive seal Felt packing

esive seal to 7)

Wood with adhesive seal and felt packing (sample 8)

ed for permeability measurements.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 20 40 60 80 100RH (%)

Xeq (k

g wat

er.k

g dm

-1)

20°C30°C40°C50°C60°C

Fig. 8. Experimental sorption isotherms for pine wood.

Table 2GAB’s constants and specific surface Sm for different temperatures.

T (�C)

20 30 40 50 60

C 12.60 11.08 8.40 8.84 10.23Xmðkgwater kg�1

dmÞ 0.00723 0.00705 0.00663 0.00556 0.00474K 0.747 0.758 0.770 0.808 0.832Sm (m2 g�1) 2542 2477 2330 1956 1668

S. Raji et al. / Construction and Building Materials 23 (2009) 3189–3195 3193

quadratic differences between the experimental and theoreticalcurves, as well as the estimated value of the specific surface areaSm calculated using relationship (2). It should be noticed that thespecific surface area decreases in a continuous manner as temper-ature increases, which may be explained by some pores beingclosed due to the expansion of the solid matrix.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 20 40 60 80 100RH (%)

Xeq (k

g wat

er.k

g dm

-1)

Linked water Interstitial water

Fig. 9. Experimental points and sorption isotherm calculated with the GAB modelat 20 �C.

Table 3Experimental values of density of pine wood according to the moisture content.

X (kgwater kg�1dm) Nr q (kg m�3) qdry (kg m�3) qcalculated (kg m�3) Deviatio

0.038 1 421 410 399 5.30.040 2 406 397 399 1.60.062 3 405 390 404 0.10.079 4 398 379 408 2.60.100 5 401 374 413 3.00.109 6 437 408 415 5.10.127 7 441 415 419 5.00.143 8 424 394 422 0.40.168 9 412 384 427 3.70.255 10 427 380 445 4.2

By way of example, Fig. 9 shows the experimental points andcurve calculated using the GAB model for the pine at 20 �C. Thestandard relation deviation between the experimental points andthe GAB simulated points is less than 2.2%. This result suggests thatthe sorption isotherms of the pine are properly described by theGAB model. It should be noted that the pine water content is quitesignificantly dependent on the relative humidity of the surround-ing air.

3.2. Density

The high dispersion of the dry density qdry values (see Table 3),as measured on 20 different samples, reveals the heterogeneity ofthe pinewood used in the present study, since all the samples usedwere derived from the same wood part.

Using the average value qdry = 390 kg m�3, the standard devia-tion of the difference between the measured values q and the cal-culated values qcalculated is 2.0% with a maximum deviation of 6.6%,which is quite acceptable. In conclusion, the volume additivitymodel can be retained for the pine, and both the density and moistvolume can be calculated with good accuracy using relationships(5) and (6) and using the value qdry = 390 kg m�3.

3.3. Thermal conductivity and effusivity

The results obtained using the hot strip method in the directionperpendicular to the wood fibres are shown in Figs. 10 and 11.

The experimental thermal effusivity E|| values as well as the cal-culated thermal conductivity k|| values in the direction of the fibresare also shown in Figs. 10 and 11.

The dispersion of the experimental points in Figs. 10 and 11 canbe explained by the fact that the measurements were made on dif-ferent samples – which showed significant dry density variations(between 364 and 415 kg m�3) despite being derived from thesame wood part.

In Figs. 10 and 11, it should be noticed that, at low humidity val-ues ðX < 0:012 kgwater kg�1

dmÞ, the effusivity and thermal conductiv-ity values are significantly higher in the direction of the fibres thanin the direction perpendicular to the fibres: E|| > E\ and kjj > k?.This can be explained by the fact that, in the absence of free water,conduction is essentially provided by the fibres. On the other hand,at X > 0:012 kgwater kg�1

dm, E|| � E\ and kjj � k? since, in this case,conduction is mainly provided by the free water in the material.This result is consistent with the sorption isotherm achieved at20 �C, as shown in Fig. 9, which shows that the presence of freewater begins at a water content close to 0:012 kgwater kg�1

dm.To conclude, it should be noted that the thermal properties of

the pine greatly depend on the water content thereof. As a result,it will prove difficult to simply take into account an average valueof this conductivity to simulate humidity variations in a wall. Thepresence of an adhesive seal does not affect heat transfer since itsthermal conductivity is higher than that of the pine. The heat flow

n (%) Nr q (kg m�3) qdry (kg m�3) qcalculated (kg m�3) Deviation (%)

11 374 364 399 6.612 406 396 400 1.613 413 398 405 2.014 405 387 409 0.915 386 364 412 6.716 418 390 415 0.717 434 407 419 3.518 415 383 422 1.719 431 401 428 0.820 434 387 445 2.6

200

300

400

500

600

0 0.05 0.1 0.15 0.2 0.25 0.3

X (kgwater.kgdm-1)

Ther

mal

effu

sivi

ty

Fig. 10. Thermal effusivity E\ (N) in the direction perpendicular to the fibres and E||

(j) in the direction parallel to the fibres as a function of water content.

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.05 0.1 0.15 0.2 0.25 0.3X (kgwater .kgdm

-1)

Ther

mal

con

dctiv

ity

Fig. 11. Thermal conductivity k\ (N) in the direction perpendicular to the fibres andk|| (j) in the direction parallel to the fibres as a function of water content.

y = 3E-05x - 0.0351R2 = 0.9992

y = 2E-05x + 0.0202R2 = 0.9995

y = 1E-05x - 0.0116R2 = 0.9998

0

1

2

3

4

5

0 50000 100000 150000 200000 250000 300000t (s)

Exch

ange

d m

ass

(g)

Fig. 12. Water mass exchanged through the sample as a function of time in agravimetric method with solid wood samples.

Table 4Pine wood mass diffusion coefficient at 30 �C.

Salts Adhesive seal X ðkgwater kg�1dmÞ X ðkgwater kg�1

dmÞ Xf ðkgwat

1 MgCl2/K2SO4 No 0.10 0.186 0.1522 NaBr/K2SO4 No 0.11 0.186 0.1563 NaCl/K2SO4 No 0.13 0.186 0.1644 MgCl2/K2SO4 Yes 0.10 0.186 0.1355 NaBr/K2SO4 Yes 0.11 0.186 0.1436 NaCl/K2SO4 Yes 0.13 0.186 0.148

3194 S. Raji et al. / Construction and Building Materials 23 (2009) 3189–3195

through the wall, and in particular through the felt packing, may beignored due the small thickness and low thermal conductivitythereof (with a measured value of 0.06 W m�1 �C�1 using the hotstrip method).

3.4. Diffusion coefficient

The water vapour diffusion coefficient in pine was measuredusing the gravimetric method. By way of example, the mass valuesmeasured for the (Small vessel + Sample + Saturated saline solu-tion) set on the solid wood samples are shown in Fig. 12. The linearvariation in mass is clear, and the slope dm/dt of these curves isevaluated using a linear regression. The diffusion coefficient DH2O

values listed in Table 4 are calculated using relationship (8). Theaverage diffusion coefficient is 5.11 � 10�9 m2 s�1 for the solidwood; in contrast, the diffusion coefficient of the laminated woodproves to be linked to the wood water content value.

Fig. 13 shows the water content variations in both the solid andlaminated woods with the same couple of saline solutions. In thecase of the solid wood, this profile can be considered linear in afirst approximation. A more subtle analysis reveals that it is actu-ally not entirely linear but shows instead a change in slope for awater content logically corresponding with the occurrence of freewater, i.e. 0:012 kgwater kg�1

dm. On the other hand, in the case ofthe laminated wood, the profile is essentially linear on the sideof the wood in contact with the higher relative humidity, but adrop in water content is visible at the adhesive seal, which revealsa resistance to diffusion at the level of the seal. Therefore, the pres-ence of an adhesive seal reduces water vapour diffusion throughthe wall.

3.5. Permeability

The results of the permeability measurements are listed inTable 5. The permeability of the sample Nr8 (Laminated log withfelt packing) has been calculated for a square metre of a wall.

It should be noted that, using the experimental device devel-oped to measure permeability on a relatively large surface (a discof 150 mm in diameter), reproducible results can be achieved, con-sidering the low standard deviations recorded. In addition, itshould be noticed that quite homogeneous results are achievedwith both the solid and laminated sample grades. In this way,the following average permeability values can be retained:5.8 � 10�17 m2 for the solid pinewood, and 7.8 � 10�18 m2 for thelaminated pinewood. Thus, the presence of an adhesive seal hasa very strong influence on air permeability, which is divided by afactor of about 7.5.

On the other hand, a sample including a felt packing proves tohave a permeability approximately 100 times higher than solidwood, and 1000 times higher that laminated wood. Consideringthe very big differences between the values recorded with andwithout the felt packing, the permeability value of Sample 8 canbe equated with that of the felt packing.

In conclusion, it should be noted that the presence of an adhe-sive seal greatly slows the air flow induced through the wood by a

er kg�1dmÞ M (g) dm/dt (kg s�1) V0 (m3) d (m) D (m2 s�1)

34.88 2.54 � 10�5 6.54 � 10�5 5.89 � 10�3 5.37 � 10�9

32.24 1.55 � 10�5 6.93 � 10�5 5.83 � 10�3 4.89 � 10�9

33.20 1.32 � 10�5 6.61 � 10�5 5.83 � 10�3 4.98 � 10�9

40.00 1.16 � 10�5 6.96 � 10�5 5.83 � 10�3 2.53 � 10�9

34.86 1.21 � 10�5 6.86 � 10�5 5.83 � 10�3 3.45 � 10�9

38.95 1.23 � 10�5 6.96 � 10�5 5.75 � 10�3 4.70 � 10�9

0.1

0.12

0.14

0.16

0.18

0.2

0 5 10 15 20 25 30Thickness (cm)

X (k

g wat

er.k

g dm

-1)

Wood with adhesive sealSolid wood

Position of adhesive seal

Fig. 13. Profile of water content in solid and laminated wood.

Table 5Results of air permeability measurements for laminated log and for laminated logwith felt packing.

Sample nr Description Thickness(mm)

Permeability(m2)

Standarddeviation (%)

1 Solid wood 20 4.11 � 10�17 0.322 28 7.66 � 10�17 0.193 42 6.26 � 10�17 0.164 46 5.19 � 10�17 0.055 Laminated log 19 8.25 � 10�18 0.506 32 8.42 � 10�18 1.097 120 6.59 � 10�18 0.538 Laminated log with

felt packing120 4.43 � 10�15 0.44

S. Raji et al. / Construction and Building Materials 23 (2009) 3189–3195 3195

pressure differential (e.g. the pressure produced by stopping thewind velocity on the outer side) between both faces of a wall. Suchair flow reduction may adversely result in lower water vapourtransfers through the wood, and contribute to the formation of‘‘moist areas”. At part level, this influence is low, considering thevery high permeability of the wall at the felt packing which is pri-marily permeated by air.

4. Conclusions

The hygrothermal analysis of a vertically laminated solid-woodwall reveals the presence of three flows through such a wall: a heatflow, a moist air flow, and a (diffusive) water vapour flow. Thesethree flows follow two parallel paths through the wall, as far as

unidirectional transfers are considered (Fig. 2). The physical prop-erties of each constitutive element of the wall have been deter-mined. It has emerged from this experimental study that thethermal properties of wood greatly depend on humidity, and theadhesive seal plays a key role for air flow and water vapour diffu-sion through the wall. Moreover, the major role of a highly perme-able felt packing has been demonstrated.

The values of such properties will be input into a model for sim-ulating how the flows through a laminated solid-wood wall evolveunder transient conditions. In situ measurements are currentlybeing carried out on log houses to validate this model. An analysisof these flows, in particular the heat flow, will make it possible tovalue the relevance of the heat resistance criterion imposed by theFrench thermal regulations for walls.

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